ALBERT

Description: This article discusses the use of numerical optimization procedures to aid in the calibration of turbulence model coefficients. Such methods would increase the rigor and repeatability of the calibration procedure by requiring clearly defined and objective optimization metrics, and could be used to identify unique combinations of coefficient values for specific flow problems. The approach is applied to the re-calibration of an explicit algebraic Reynolds stress model for the incompressible planar mixing layer using the Nelder-Mead simplex algorithm and a micro-genetic algorithm with minimally imposed constraints. Three composite fitness functions, each based upon the error in the mixing layer growth rate and the normal and shear components of the Reynolds stresses, are investigated. The results demonstrate a significant improvement in the target objectives through the adjustment of three pressure-strain coefficients. Adjustments of additional coefficients provide little further benefit. Issues regarding the effectiveness of the fitness functions and the efficiency of the optimization algorithms are also discussed.

Description: This manual describes the installation and execution of FUN3D (Fully-UNstructured three-dimensional CFD (Computational Fluid Dynamics) code) version 13.5, including optional dependent packages. FUN3D is a suite of computational fluid dynamics simulation and design tools that uses mixed-element unstructured grids in a large number of formats, including structured multiblock and overset grid systems. A discretely-exact adjoint solver enables efficient gradient-based design and grid adaptation to reduce estimated discretization error. FUN3D is available with and without a reacting, real-gas capability. This generic gas option is available only for those persons that qualify for its beta release status.

Description: A computational fluid dynamics code has been developed for large-eddy simulations (LES) of turbulent flow. The code uses high-order of accuracy and high-resolution numerical methods to minimize solution error and maximize the resolution of the turbulent structures. Spatial discretization is performed using explicit central differencing. The central differencing schemes in the code include 2nd- to 12th-order standard central difference methods as well as 7-, 9-, 11- and 13-point dispersion relation preserving schemes. Solution filtering and high-order shock capturing are included for stability. Time discretization is performed using multistage Runge-Kutta methods that are up to 4th order accurate. Several options are available to model turbulence including: Baldwin-Lomax and Spalart-Allmaras Reynolds-averaged Navier-Stokes turbulence models, and Smagorinsky, Dynamic Smagorinsky and Vreman sub-grid scale models for LES. This report presents the theory behind the numerical and physical models used in the code and provides a user's manual to the operation of the code.

Description: No abstract available

Description: The Predictive Thermal Control (PTC) technology development project is a multiyear effort initiated in Fiscal Year (FY) 2017, to mature the Technology Readiness Level (TRL) of critical technologies required to enable ultra-thermally-stable telescopes for exoplanet science. A key PTC partner is Harris Corporation (Rochester NY).

Description: Experiments are being conducted in the NASA Ames Hypervelocity Free Flight Aerodynamic Facility to quantify the effects on turbulent convective heat transfer of surface roughness representative of a new class of 3D woven thermal protection system mRough-wall turbulent heat transfer measurements were obtained on ballistic-range models in hypersonic flight in the NASA Ames Hypervelocity Free Flight Aerodynamic Facility. Each model had three different surface textures on segments of the conic frustum: smooth wall, sand roughness, and a pattern roughness, thus providing smooth-wall and sand-roughness reference data for each test. The pattern roughness was representative of a woven thermal protection system material developed by NASA's Heatshield for Extreme Entry Environment Technology project. The tests were conducted at launch speeds of 3.2 km/s in air at 0.15 atm. Roughness Reynolds numbers, k+, ranged for 12 to 70 for the sand roughness, and as high as 200 for the pattern roughness. Boundary-layer parameters required for calculating k+ were evaluated using computational fluid dynamics simulations. The effects of pattern roughness are generally characterized by an equivalent sand roughness determined with a correlation developed from experimental data obtained on specifically-designed roughness patterns that do not necessarily resemble real TPS materials. Two sand roughness correlations were examined: Dirling and van Rij, et al. Both gave good agreement with the measured heat-flux augmentation for the two larger pattern roughness heights tested, but not for the smallest height tested. It has yet to be determined whether this difference is due to limitations in the experimental approach, or due to limits in the correlations used. Future experiments are planned that will include roughness patterns more like those used in developing the equivalent sand roughness correlations.aterials being developed by NASA's Heatshield for Extreme Entry Environment Technology (HEEET) project. Data were simultaneously obtained on sand-grain roughened surfaces and smooth surfaces, which can be compared with previously obtained data. Results are presented in this extended abstract for one roughness pattern. The full paper will include results from three roughness patterns representing virgin HEEET, nominal turbulent ablated HEEET, and twice the roughness of nominal turbulent ablated HEEET. Results will be used to compare with commonly used equivalent sand grain roughness correlations.

Description: Over the last 5 years, the Heatshield for Extreme Entry Environment Technology (HEEET) project has been working to mature a 3-D Woven Thermal Protection System (TPS) to Technical Readiness Level (TRL) 6 to support future NASA missions to destinations such as Venus and Saturn. A key aspect of the project has been the development of the manufacturing and integration processes/procedures necessary to build a heat shield utilizing the HEEET 3D-woven material. This has culminated in the building of a 1-meter diameter Engineering Test Unit (ETU) representative of what would be used for a Saturn probe. The present talk provides an overview of recent testing of NASA's Heatshield for Extreme Entry Environment Technology (HEEET) 3D Woven TPS. Under the current program, the ETU has been subjected to Thermal and Mechanical loads typical of deep space mission to Saturn. Thermal testing of HEEET coupons has performance up to 4,500 watts per centimeter squared at 5 atmospheres stagnation pressure and successful shear performance up to 3000 pascals at 1,650 watts per centimeter squared at 2.6 atmospheres pressure.

Description: Laser Rayleigh scattering was used to investigate clusters in the free-stream flow at Arnold Engineering Development Centers Tunnel 9 (T9). The facility was run at Mach-14, with a pure-N2 flow medium, and at several total pressures and temperatures. Using an excimer laser operating at 248 nm, the Rayleigh instrument imaged scattering from the focused laser beam in the free-stream. As a wind-tunnel flow is accelerated, it cools and approaches the condensation boundary. As a precursor to condensation, small clusters of molecules are first formed, but the individual clusters are too small to be spatially resolved in typical images of the beam. Thus clusters effectively add a spatially smooth background signal to the pure diatomic-molecule Rayleigh signal. The main result of the present work is that clustering was not significant. After correcting for interference by small particles imbedded in the T9 flow, cluster scattering was unobservable or smaller than one standard deviation (1-sigma) of the uncertainties for almost all tunnel runs. The total light scattering level was measured to be 1.05 +/- 0.15 (1-sigma) of the expected diatomic scattering, when averaged over the entire usable data set. This result included flow conditions that were supercooled to temperatures of ~ 20 K, about 25 K below the condensation limit of ~ 45 K. Thus the Mach-14 nozzle flow is essentially cluster-free for many supercooled conditions that might be used to extend the facility operating range to larger Reynolds numbers.

Description: Mission, landing and recovery operations for the Orion crew module involve reentry into the Earth's atmosphere and the deployment of three Nomex parachutes to slow the descent before landing along the west coast of the United States. Orion may have residual fuel (hydrazine, N2H4) or coolant (ammonia, NH3) on board which are both highly toxic to crew in the event of exposure. These risks were evaluated using a first principles analysis approach through fluid dynamics modeling. Plume calculations were first performed with the ANSYS Fluent computational fluid dynamics code. Data were then extracted at locations relevant to crew safety such as the snorkel fan inlet and the egress hatch. Mixing calculations were performed to quantify exposure concentrations within the crew bay before and during egress and departure. Finally, results included herein were used to inform the Orion post-landing Concept of Operations (ConOps) so that strategies could be formulated to maintain crew safety in the event of the loss of fuel or coolant.

Description: During instrument-level or spacecraft-level ground testing, heat pipes may be placed in reflux mode, with condenser above evaporator. A liquid pool will form at the bottom of the heat pipe. If heat is applied to a site below the surface of the liquid pool in a vertical heat pipe, the heat pipe can work properly under reflux mode. A superheat is required for startup. If heat is applied to a site above the liquid pool, the heat pipe is not expected to work unless additional heat is applied to the liquid pool to provide the needed flow circulation. There are many reason to minimize the additional heater power. An experimental investigation was conducted to study the heat pipe behavior under this configuration.

Description: In this report we have catalogued the flow regimes observed in microgravity, summarized correlations for the pressure drop and rate of heat transfer that are commonly used, and discuss the validation of a few correlations from available experimental results. Two-phase flow through some specific components such as bends, tees, filters and pumps are discussed from a physical perspective to guide the designer on how reduced gravity might affect their performance. Phase separation in zero gravity is addressed through the behavior and basic design concepts for devices based on passive centrifugal action, capillary forces, gas extraction through a membrane installed in a channel wall and the use of a syringe with a perforated piston to remove bubbles from small liquid volumes. We address the common instabilities that develop in flow loops owing exclusively to the two-phase nature of the flow, e.g., Ledinegg instability and concentration waves. Finally we briefly review flow metering and gauging; two-phase flow through porous media, where pressure drop and flow regime map correlations in zero-g are a current research topic; and basic operation principles of heat pipes and capillary pumped loops.

Description: Current turbulence models, such as those employed in Reynolds-averaged Navier-Stokes CFD, are unable to reliably predict the onset and extent of the three-dimensional separated flow that typically occurs in wing-fuselage junctions. To critically assess, as well as to improve upon, existing turbulence models, experimental validation-quality flow-field data in the junction region is needed. In this report, we present an overview of experimental measurements on a wing-fuselage junction model that addresses this need. The experimental measurements were performed in the NASA Langley 14- by 22-Foot Subsonic Tunnel. The model was a full-span wing-fuselage body that was configured with truncated DLR-F6 wings, both with and without leading-edge extensions at the wing root. The model was tested at a fixed chord Reynolds number of 2.4 million, and angles-of-attack ranging from -10 degrees to +10 degrees were considered. Flow-field measurements were performed with a pair of miniature laser Doppler velocimetry (LDV) probes that were housed inside the model and attached to three-axis traverse systems. One LDV probe was used to measure the separated flow field in the trailing-edge junction region. The other LDV probe was alternately used to measure the flow field in the leading-edge region of the wing and to measure the incoming fuselage boundary layer well upstream of the leading edge. Both LDV probes provided measurements from which all three mean velocity components, all six independent components of the Reynolds-stress tensor, and all ten independent components of the velocity triple products were calculated. In addition to the flow-field measurements, static and dynamic pressures were measured at selected locations on the wings and fuselage of the model, infrared imaging was used to characterize boundary-layer transition, oil-flow visualization was used to visualize the separated flow in the leading- and trailing-edge regions of the wing, and unsteady shear stress was measured at limited locations using capacitive shear-stress sensors. Sample results from the measurement techniques employed during the test are presented and discussed.

Description: The InSight Mars Lander successfully landed on the surface on November 26, 2018. This poster will describe the methodologies and margins used in developing the aerothermal environments for design of the thermal protection systems (TPS), as well as a prediction of as-flown environments based on the best estimated trajectory. The InSight mission spacecraft design approach included the effects of radiant heat flux to the aft body from the wake for the first time on a US Mars Mission, due to overwhelming evidence in ground testing for the European ExoMars mission (2009/2010) [1] and 2010 tests in the Electric Arc Shock Tube (EAST) facility [2]. The radiant energy on an aftbody was also recently confirmed via measurement on the Schiaparelli mission [3]. In addition, the InSight mission expected to enter the Mars atmosphere during the dust storm season, so the heatshield TPS was designed to accommodate the extra recession due to the potential dust impact. This poster will compare the predicted aerothermal environments using the reconstructed best estimated trajectory to the design environments. Design Approach: The InSight spacecraft was planned to be a near-design-to-print copy of the Phoenix spacecraft. The determination of the heatshield TPS requirements was approached as if it was a new design due to the new requirement of flying through a dust storm. The baseline for aftbody was build-to-print, and all analyses focused on ensuring adequate margin. This proved to be a challenge because the Phoenix aftbody was designed to withstand only convective heating and the InSight aftbody was evaluated for both convective and radiative heating. Aerothermal environments were predicted using the Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA) and the Data Parallel Line Relaxation (DPLR) CFD codes, and the Nonequilibrium Radiative Transport and Spectra Program (NEQAIR) utilizing bounding design trajectories derived from Monte Carlo analyses from the Program to Optimize Simulated Trajectories II (POST2). In all cases, super-catalytic flowfields were assigned to ensure the most conservative heating results. Two trajectories were evaluated: 1) the trajectory with the maximum heat flux was utilized to determine the flowfield characteristics and the viability of the selection of TPS materials; and 2) the trajectory with the maximum heat load was used to determine the required thicknesses of the TPS materials. Evaluation of the MEDLI data [4], along with ground test data [5] led to the determination of whether or not the flow would transition from laminar to turbulent on the heatshield, which also determined the TPS sizing location for the heatshield. Aerothermal margins were added for the convective heating and developed for the radiative heating. TPS material sizing was determined with the Reaction Kinetic Ablation Program (REKAP) and the Fully Implicit Ablation and Thermal Analysis program (FIAT) using a three-branched approach to account for aerothermal, material response, and material properties uncertainties. In addition, the heatshield recession was augmented by an analysis of the effect of entry through a potential dusty atmosphere using a methodology developed in References [6] and [7]. These analyses resulted in an increase to the Phoenix heatshield TPS thickness. Reconstruction Efforts: Once the best estimated trajectory is reconstructed by the team, the LAURA/HARA (High-Temperature Aerothermo-dynamic Radiation model) and DPLR/NEQAIR code pairs will be used to predict the as-flown aerothermal conditions. In these runs, fully-catalytic flowfields will be assigned because it is a more physically accurate description of the chemistry in the flow. Once again, determination of the onset of turbulence on the heatshield will be evaluated. The as-flown aerothermal environments will then be compared to the design environments.

Description: Abstract and not the Final document is attached. Low Lunar orbit presents a unique thermal environment with high planetary and high solar IR requirements. Orion requires a phase change material heat exchanger (PCM HX) to act as a supplemental heat rejection device (SHReD) during this orbit. As a result, Orion currently uses a PCMHX to meet heat rejection demands in low lunar orbit. This PCM HX weighs 145 lbs, a significant amount of weight on the Crew Module Adaptor. To reduce this weight, a new PCM HX and phase change material is being proposed. This new PCM HX, constructed by Mezzo technologies, was originally designed as a water based PCM HX but is now be repurposed for phase change materials with transition temperatures in Orion's set points and different freeze front propagations. Mezzo's PCM HX utilizes micro tubes which greatly increase the overall heat transfer efficiency allowing for a compact design and significant weight savings. A new phase change material is also being proposed which has a higher latent heat of fusion as well as a higher density. This paper investigates the design, testing, and analysis done on the new Mezzo PCM HX as well as the corresponding phase change material.

Description: Computational ice shapes were generated on the boundary layer ingesting engine nacelle of the D8 Double Bubble aircraft. The computations were generated using LEWICE3D, a well-known CFD icing post processor. A 50-bin global drop diameter discretization was used to capture the collection efficiency due to the direct impingement of water onto the engine nacelle. These discrete results were superposed in a weighted fashion to generate six drop size distributions that span the Appendix C and O regimes. Due to the presence of upstream geometries, i.e. the fuselage nose, the trajectories of the water drops are highly complex. Since the ice shapes are significantly correlated with the collection efficiency, the upstream fuselage nose has a significant impact on the ice accretion on the engine nacelle. These complex trajectories are caused by the ballistic nature of the particles and are thus exacerbated as particle size increases. Shadowzones are generated on the engine nacelle, and due to the curvature of the nose of the aircraft the shadowzone boundary moves from lower inboard to upper outboard as particle size increases. The largest particle impinging one the engine nacelle from the 50-bin discretization was the 47 um drop diameter. As a result, the MVD greater than 40 um Appendix O conditions were characterized by extremely low collection efficiency on the engine nacelle for these direct impingement simulations.

Description: Radiative heating computations are performed for high speed lunar return experiments conducted in the Electric Arc Shock Tube (EAST) facility at NASA Ames Research Center. The nonequilibrium radiative transport equations are solved via NASA's in-house radiation code NEQAIR using flow field input from US3D flow solver. The post-shock flow properties for the 10 km/s Earth entry conditions are computed using the stagnation line of a blunt-body and a full facility CFD (Computational Fluid Dynamics) simulation of the EAST shock tube. The shocked gas in the blunt-body flow achieves a thermochemical equilibrium away from the shock front whereas EAST flow exhibits a nonequilibrium behavior due to strong viscous dissipation of the shock by boundary layer. The full-tube flow calculations capture the influence of the boundary layer on the shocked gas state and provide a realistic fluid dynamic input for the radiative predictions. The integrated radiance behind the shock is calculated in NEQAIR for wavelength regimes from Vacuum-UltraViolet (VUV) to InfraRed (IR), which are pertinent to the emission characteristics of high enthalpy shock waves in air. These radiance profiles are validated against corresponding EAST shots. The full-tube simulations successfully predict a sharp radiance peak at the shock front which gets smeared in the test data due to the spatial resolution in the measurements. The full facility based radiance behind the shock shows a slightly better match with the test data in the VUV and Red spectral regions, as compared to that from a blunt-body based predictions. The UV radiance is very similar for both geometries and under-predicts the test behavior. The IR test data matches better with the blunt-body based predictions where the full-tube simulations show a significant over-prediction.

Description: Numerical investigations of the flowfield inside NASA Ames' Electric Arc Shock Tube have been performed. The focus is to simulate the experiments designed to reproduce shock layer radiation layer relevant to Earth re-entry conditions. This paper assess the current computational capability in simulating time-accurate unsteady nonequilibrium flows in the presence of strong shock waves with state-of-the-art physical models. The technical approach is described with preliminary results presented for one specific flow condition. It was found that the axisymmetric source term generates a numerical instability that appears as shock bending. This instability is time dependent which greatly affects the shock speed. Post-shock conditions are discussed and compared to CEA equilibrium prediction and good agreement was obtained close to the test-section and just behind the shock.

Description: The HEEET project was conceived to develop a heatshield with a high performance ablative thermal protection material that can withstand the extreme entry environment produced as a result of rapid deceleration during high speed entry into Venus, Saturn, Uranus or higher speed entry into Earth's atmosphere. Successful maturation of HEEET supports future New Frontiers and Discovery AO's, as well as Flagship and directed missions in the longer term. In addition, HEEET has the potential to evolve and to support re-entry to Earth, for missions such as Mars Sample Return.The primary goal of the HEEET Project was to develop an ablative TPS heat-shield based on woven TPS technology to Technology Readiness Level (TRL) 6. Key evidence to support the TRL evaluation includes: Demonstration of reproducible manufacturing of a dual layer material over a range of thicknesses and integrated on to a heatshield engineering test unit at a scale that is applicable to near term Discovery as the highest priority and future NF missions as secondary priority set of missions. Demonstration of predictable and stable performance of the dual layer TPS over a range of entry environments that are applicable to near term Discovery and NF missions of interest to SMD.Includes completion of coupon arc jet and laser testing and development of a mid-fidelity thermal response model that correlates with test results. Demonstration of flight heatshield system design for a range of sizes and loads that are relevant to near term Discovery and NF missions of interest to SMD. Includes completion of structural testing to validate analytic thermal/structural models and development of a material property database. Includes structural testing of a ~1m Engineering Test Unit under relevant entry loads.

Description: This paper reports computational analyses and flow characterization studies in a high enthalpy arc-jet facility at NASA Ames Research Center. These tests were conducted using a wedge model placed in a free jet downstream of new 9-inch diameter conical nozzle in the Ames 60-MW Interaction Heating Facility. Both the nozzle and wedge model were specifically designed for testing in the new Laser-Enhanced Arc-jet Facility. Data were obtained using stagnation calorimeters and wedge models placed downstream of the nozzle exit. Two instrumented wedge calibration plates were used: one water-cooled and the other RCG-coated tile plate. Experimental surveys of arc-jet test flow with pitot and heat flux probes were also performed at three arc-heater conditions, providing assessment of the flow uniformity and valuable data for the flow characterization. The present analysis comprises computational fluid dynamics simulations of the nonequilibrium flowfield in the facility nozzle and test box, including the models tested, and comparisons with the experimental measurements. By taking into account nonuniform total enthalpy and mass flux profiles at the nozzle inlet as well as the expansion waves emanating from the nozzle exit and their effects on the model flowfields, these simulations approximately reproduce the probe survey data and predict the wedge model surface pressure and heat flux measurements.

Description: Recently, heat transfer correlations based on liquid nitrogen (LN2) and liquid hydrogen (LH2) pipe quenching data were developed to improve the predictive accuracy of lumped node codes like SINDA/FLUINT and the Generalized Fluid System Simulation Program (GFSSP). After implementing these correlations into both programs, updated model runs showed strong improvement in LN2 pipe chilldown modeling but only modest improvement in LH2 modeling. Due to large differences in thermal and fluid properties between the two fluids, results indicated a need to develop a separate set of LH2-only correlations to improve the accuracy of the simulations. This paper presents a new set of two-phase convection heat transfer correlations based on LH2 pipe quenching data. A correlation to predict the bulk vapor temperature was developed after analysis showed that high amounts of thermal nonequilibrium of the liquid and vapor phases occurred during film boiling of LH2. Implemented in a numerical model, the new correlations achieve a mean absolute error of 19.5 K in the predicted wall temperature when compared to recent LH2 pipe chilldown data, an improvement of 40% over recent GFSSP predictions. This correlation set can be implemented in simulations of the transient LH2 chilldown process. Such simulations are useful for predicting the chilldown time and boil-off mass of LH2 for applications such as the transfer of LH2 from a ground storage tank to the rocket vehicle propellant tank, or through a rocket engine feedline during engine startup.

Description: Film cooling is used in a wide variety of engineering applications for protection of surfaces from hot or combusting gases. The design of more efficient film cooling geometries/configurations could be facilitated by an ability to accurately model and predict the effectiveness of current designs using computational fluid dynamics (CFD) code predictions. Hence, a benchmark set of flow field property data were obtained for use in assessing current CFD capabilities and for development of better modeling approaches for these turbulent flow fields where accurate calculation of turbulent heat flux is important. Both Particle Image Velocimetry (PIV) and spontaneous rotational Raman scattering (SRS) spectroscopy were used to acquire high quality, spatially-resolved measurements of the mean velocity, turbulence intensity as well as the mean temperature and root mean square (rms) temperatures in a film cooling flow field. In addition to off-body flow field measurements, infrared thermography (IR) and thermocouple measurements on the plate surface enabled estimates of the film effectiveness. Raman spectra in air were obtained across a matrix of axial locations downstream from a 68.07 mm square nozzle blowing heated air over a range of temperatures (up to TR = 2.7) and Mach numbers (up to M0.9), across a 30.48 cm long plate equipped with three patches of 45 small (~1 mm) diameter cooling holes arranged in a staggered configuration. In addition, both centerline streamwise 2-component PIV and cross-stream 3-component Stereo PIV data at 14 axial stations were collected in the same flows. Only a subset of the data collected in the test program is included in this Part I report and are available from the NASA STI office. The final portion of the data will be published in a future report, Part II, along with CFD predictions of the complex cooling film flow.

Description: This summer internship is focused on using CFD and fluid mechanics to optimize the SRL-ADEPT geometry in an attempt to increase drag and area-effectiveness, and reduce flow separation.

Description: ESA recently flew an entry, descent, and landing demonstrator module called Schiaparelli that entered the atmosphere of Mars on the 19th of October, 2016. The instrumentation suite included heatshield and backshell pressure transducers and thermocouples (known as AMELIA) and backshell radiation and direct heatflux-sensing sensors (known as COMARS and ICOTOM). Due to the failed landing of Schiaparelli, only a subset of the flight data was transmitted before and after plasma black-out. The goal of this paper is to present comparisons of the flight data with calculations from NASA simulation tools, DPLR/NEQAIR and LAURA/HARA. DPLR and LAURA are used to calculate the flowfield around the vehicle and surface properties, such as pressure and convective heating. The flowfield data are passed to NEQAIR and HARA to calculate the radiative heat flux. Comparisons will be made to the COMARS total heat flux, radiative heat flux and pressure measurements. Results will also be shown against the reconstructed heat flux which was calculated from an inverse analysis of the AMELIA thermocouple data performed by Astrium. Preliminary calculations are presented in this abstract. The aerodynamics of the vehicle and certain as yet unexplained features of the inverse analysis and forebody data will be investigated.

Description: NASA's Descent System Studies (DSS) Program is studying various concept vehicles to enable landing of heavy payloads on the surface of Mars. While it is desirable to run high-fidelity CFD simulations to accurately assess the aerodynamic and aerothermal effects of various design changes during EDL, it is usually difficult to quickly generate high-quality grids suitable for such analyses. One approach to address this bottleneck in mesh generation is through the use oversetting grids. Although the overset approach is efficient and powerful in solving partial differential equations on complex geometries, new users often find it challenging to apply overset concepts for their simulations. For example, generating hyperbolic grids with sufficient overlap; priority in hole-cutting on multiple overlapping grids; and fixes to assemble overlapping viscous grids at the body surface. The objective of this presentation is to introduce a simple process that combines the advantages of near-body, point-matched, structured grids with oversetting background grids suitable for grid alignment. This approach allows for grids that can be sequenced, reclustering of mesh spacing at the wall, and grid alignment with the bow shock. The current methodology is tested on a Mid-L/D configuration using the overset DPLR code.

Description: Electronics Boxes with high heat dissipations use a thermal interface material to increase heat transfer to the radiator in a vacuum/space environment. There are lots of materials to choose from, but for Spacecraft applications, there are more than high heat transfer metrics which must be met. Contamination (both particle generation and outgassing), ease of cutting, and removal are just as important metrics in material selection. However, vendor data of material thermal conductance is usually based on a 1" X 1" piece of material under high uniform pressures. Large Electronics boxes almost never have optimal pressures, as they are bolted along the perimeter and leave gaps in the center regions. In order to characterize the relative thermal conductance for large Electronics boxes, an 8" X 8" plate was fabricated to simulate an electronics box bottom and bolted around the perimeter to a cold plate. Various thermal interface materials were inserted between the box and cold plate, and overall thermal conductance's were calculated. A table was generated which compares the full gamut of thermal interface materials for large boxes, from a dry joint to a wet joint. Materials were placed in order of high to low conductance's, so an engineer can compare the benefit of each material in a real-world scenario.

Description: The intermediate wake region of a thick flat plate with a circular trailing edge (TE) is investigated with a direct numerical simulation (DNS). The upper and lower separating boundary layers are both turbulent and are statistically identical; the resulting wake is symmetric in the mean. Earlier research dealt with the near/very-near wake of the same plate (x/D 〈 13.0, x is the streamwise distance from the center of the circular TE and D is the plate-thickness/TE-diameter). In the present investigation the emphasis is on the evolution of shed-vortex structure and turbulence intensity distributions with increasing x; the focus is on the region 20.0 〈 x/D 〈 40.0. Profile similarity in wake velocity statistics is explored.

Description: Ammonia is used in the Starboard 1 (S1) and Port 1 (P1) External Active Thermal Control System (EATCS) to cool the pressurized modules, and some of the external electrical power distribution hardware. Leaks that develop in these critical cooling systems that deplete in-line tanks can ultimately result in loss of cooling, which can have devastating impacts to the mission, science and crew onboard the ISS. A slow ammonia leak was initially observed from the P1 EATCS in 2011, but later in 2013 the leak rate began to accelerate. The ammonia inventory eventually began to decay exponentially, raising concerns that the inventory could drop to levels where the system would not be operational.The Robotic External Leak Locator (RELL) was built and launched to the ISS to detect and help locate ammonia leaks using the ISS Robotic Arm and remote ground operator control without constant crew involvement. RELL pinpointed the ammonia leak to the two flexible jumper hose assemblies connecting one of two fluid loops in one of the three deployable radiators to the P1 EATCS. The ammonia inside the two hose assemblies and that radiator fluid loop was isolated and vented to space in 2017. This stopped the leak and an Extravehicular Activity was conducted to remove the two hose assemblies so they could be returned to ground for further Test, Teardown and Evaluation (TT&E). The purpose of this presentation is to discuss this leakage scenario and the TT&E efforts.

Description: Normally, in order to characterize multilayer insulation installed onto a test tank, the boil-off of the tank is measured and then heat loads from structural and fluid penetrations are calculated from temperature measurements throughout the system. For the Structural Heat Intercept, Insulation, and Vibration Evaluation Rig testing, it was determined that this approach would have significant uncertainties (over 50%) and that another method was needed to characterize the heat load through the blanket. Heat flux sensors are widely used to measure heat loads and characterize insulation systems at room temperature, however, the heat fluxes measured are usually two orders of magnitude higher than high performance MLI. Three different heat flux sensors were initially checked out on a liquid hydrogen calorimeter. One was chosen for actual implementation and 20 sensors were ordered. Of those sensors, calibration was attempted on 7 of the sensors. The results from testing and calibration are discussed.

Description: The two decades old high order central differencing via entropy splitting and summation-by-parts (SBP) difference boundary closure of Ols- son & Oliger (1994), Gerritsen & Olsson (1996), and Yee et al. (2000) is revisited. The entropy splitting is a form of skew-symmetric splitting of the nonlinear Euler flux derivatives. Central differencing applied to the entropy splitting form of the Euler flux derivatives together with SBP difference operators will, hereafter, be referred to as entropy split schemes. This study is prompted by the recent growing interest in numerical methods for which a discrete entropy conservation law holds, a discrete global entropy conservation can be proved and/or the numerical method possesses a stable entropy in the framework of SBP difference operators and L2-energy norm estimate. The objective of this paper is to recast the entropy split scheme as the re- cent definition of an entropy stable method for central differencing with SBP operators for both periodic and non-periodic boundary conditions for non- linear Euler equations. Standard high order spatial central differencing as well as high order central spatial DRP (dispersion relation preserving) spatial differencing is part of the entropy stable methodology framework. Long time integration of 2D and 3D test cases is included to show the comparison of this efficient entropy stable method with the Tadmor-type of entropy conservative methods. Studies also include the comparison among the three skew-symmetric splittings on their nonlinear stability and accuracy performance without added numerical dissipations for smooth flows. These are, namely, entropy splitting, Ducros et al. splitting and the Kennedy & Grub- ber splitting.

Description: No abstract available

Description: This paper presents numerical models of boiling in a heated tube using the Generalized Fluid System Simulation Program (GFSSP), a finite-volume-based general-purpose flow network code developed at NASA/Marshall Space Flight Center. The heated tube is discretized into a one-dimensional array of nodes and branches to represent the flow of liquid and vapor in a tube with a prescribed pressure differential. The solid wall is also discretized into solid nodes and conductors to allow for heat transfer between the wall and the fluid. The conservation equations of mass, momentum, and energy of the fluid are solved simultaneously with the energy conservation equation for the solid wall. Two experimental configurations of fluid flowing in a vertical tube have been simulated, one with water and the other with liquid hydrogen. This paper compares experimental data with numerical predictions based on four different published correlations for boiling heat transfer coefficients. Three of these correlations are applicable to the saturated vertical flow conditions of the experiments. One of them is applicable to film boiling and has been used for the liquid hydrogen experiment, which was in film boiling regime. For the case of boiling water, the predictions of wall temperatures using the boiling heat transfer correlations agreed well with the experimental results. However, in the case of boiling hydrogen larger discrepancies were observed between the experimental data and numerical predictions.

Description: No abstract available

Description: Free-Flight CFD capability has been implemented into the finite-volume solver US3D under the Entry Systems Modeling project. Several simulations of ballistic range experiments have been performed in order to validate the simulation software and methodology. Extension of the software to flight scale trajectories with varying freestream conditions has been carried out. Results show promising ability to predict vehicle behavior as compared to flight. Finally, a multi-body free-flight capability has been developed to generalize the single-body free-flight solver to study multiple bodies in proximal flight.

Description: NASAs Flight Imagery Launch Monitoring Real-time System (FILMRS) cameras were originally developed for the Space Launch System (SLS) Core Stage. These Commercial Off the Shelf (COTS) cameras have been redesigned and reduced by an order of magnitude in size for the Exploration Upper Stage (EUS). The change in thermal environment has led to the application of various passive thermal control methods and the addition of a heater option. This paper will give a summary of the design and development test effort associated with adapting the COTS camera for the demands of the space environment and associated thermal mitigations applied as the project prepares to complete the design. The application of this camera for other space systems is discussed.

Description: Active flow control (AFC) subscale experiments were conducted at the Lucas Wind Tunnel of the California Institute of Technology. Tests were performed on a generic vertical tail model at low speeds. Fluidic oscillators were used at the trailing edge of the main element (vertical stabilizer) to redirect the flow over the rudder and delay or prevent flow separation. Side force increases in excess of 50% were achieved with a 2% momentum coefficient (C(sub )) input. The results indicated that a collective C(sub ) of about 1% could increase the side force by 3050%. This result is achieved by reducing the spanwise flow on the swept back wings that contributes to early flow separation near their tips. These experiments provided the technical backdrop to test the full-scale Boeing 757 vertical tail model equipped with a fluidic oscillator system at the National Full-scale Aerodynamics Complex 40-by 80-foot Wind Tunnel, NASA Ames Research Center. The C(sub ) is shown to be an important parameter for scaling a fluidic oscillator AFC system from subscale to full-scale wind tunnel tests. The results of these tests provided the required rationale to use a fluidic oscillator AFC configuration for a follow-on flight test on the Boeing 757 ecoDemonstrator.

Description: Plant Water Management is a technology demonstration of recent advances in micro-g capillary fluidics research applied to plant growth systems. It has applications in long-term food production systems for missions to the Moon and Mars, as well as the immediate need for ISS food supplements to the crew diet. PWM will demonstrate the low-gravity role of surface tension, wetting, and system geometry to effectively replace the role of gravity in certain terrestrial plant growth systems.

Description: Numerical investigations of the ow field inside NASA Ames' Electric Arc Shock Tube have been performed. The focus is to simulate the experiments designed to reproduce shock layer radiation layer relevant to Earth re-entry conditions. This paper assess the current computational capability in simulating unsteady nonequilibrium flows in the presence of strong shock waves with state-of-the-art physical models. The technical approach is described with preliminary results presented for one specific ow condition. The numerical problems encountered during the computation of these flows are detailed, along with the methods used to resolve them. Post-shock conditions are discussed and compared to CEA equilibrium prediction.

Description: In order to improve the cryogenic propellant management technologies for a liquid hydrogen rocket with high specific impulse, JAXA, the University of Tokyo, and the NASA Glenn Research Center have jointly organized a multi-agency model validation collaboration project. As part of this project, JAXA's boiling simulation was validated with NASA's experimental data on vertical pipeline chill-down. Simulation results were in good agreement with the experimental data obtained using an improved boiling model to reproduce the spray flow. This activity achieved liquid hydrogen turbo-pump simulation at JAXA for grasping the boiling flow phenomenon from engine cut-off to re-ignition. This joint research resulted in an international cooperative relationship for discussing the cryogenic propellant management technologies necessary to develop next-generation liquid rockets.

Description: "Heat pipes are being used on many spacecraft to acquire heat dissipated by the payload and transport the heat to a remote radiator. In instrument-level or spacecraft-level ground testing, many heat pipes are placed in a gravity-driven reflux mode where the condenser is well above the evaporator, resulting in the formation of a liquid pool at the bottom of the heat pipe. If a head load is applied to a site that is in contact with the liquid pool, the generated vapor will flow upward to the condenser and the condensate will fall back to the evaporator due the influence of gravity. Hence, the heat pipe can operate steadily under reflux mode because the heated site always has sufficient liquid supply to sustain the fluid flow. In contrast, when a heat load is applied to a site remote from the liquid pool, the heat pipe will be unable to transfer heat through liquid evaporation unless the heated site has a chance to be in contact with liquid. This can be accomplished by applying an additional heat load to the liquid pool to establish a reflux flow so that the remote site can capture the falling condensate. An experimental investigation was conducted to study the effect of gravity on the thermal performance of a heat pipe under reflux mode with multiple heat loads. An aluminum ammonia heat pipe with internal axial grooves was placed in a vertical position. Cooling was provided to the top of the heat pipe, and heat was applied to three sites below the condenser with various heat distributions. One of the heated sites was above the liquid pool, and two were in direct contact with the liquid pool. Test results showed that when a heat load was applied to either one or both of the lower sites, the heat pipe could run steadily under reflux mode. After a reflux flow had been established, a heat load could be applied to the upper site. If the upper site could capture sufficient liquid falling from the condenser to handle its heat load solely by liquid evaporation, the heat pipe could reach steady operation. Otherwise, the temperature of the upper site would oscillate due to its intermittent contact with the falling liquid. For a given heat load to the upper site, the amplitude of temperature oscillation decreased with an increasing heat load to the lower sites because there was more falling condensate available for the upper site to capture. Moreover, the temperature oscillation disappeared completely when the total heat loads to lower sites exceeded a threshold power, and the threshold power increased with an increasing heat load to the upper site."

Description: NEQAIR v15.0 provides the first steps to improved coupling between NEQAIR and the DPLR CFD code, which will be fully realized in v15.1. The plan is to release NEQAIR v15.1 and DPLR 4.05 at the same time. The improvements implemented in NEQAIR v15.0 have focused on improving stability, solution robustness, usability and providing different options for running the code. It is also the first version of the code to have a new input file and line of sight format since 2009. Backward compatibility with previous formats of the input files (neqair.inp and LOS.dat) has also been provided. NEQAIR v15.0 supersedes the prerelease of this version, as well as NEQAIR v14.0, v13.2, v13.1 and the suite of NEQAIR2009 versions. These updates have predominantly been performed by Brett Cruden and Aaron Brandis from AMA Inc at NASA Ames Research Center between 2016 and 2018. NEQAIR v15.0 is a standalone software tool for line-by-line spectral computation of radiative intensities and/or radiative heat flux, with one-dimensional transport of radiation. In order to accomplish this, NEQAIR v15.0, as in previous versions, requires the specification of distances (in cm), temperatures (in K) and number densities (in parts/cc) of constituent species along lines of sight. Therefore, it is assumed that flow quantities have been extracted from flow fields computed using other tools, such as CFD codes like DPLR or LAURA, and that lines of sight have been constructed and written out in the format required by NEQAIR v15.0. There are two principal modes for running NEQAIR v15.0. In the first mode NEQAIR v15.0 is used as a tool for creating synthetic spectra of any desired resolution (including convolution with a specified instrument/slit function). The first mode is typically exercised in simulating/interpreting spectroscopic measurements of different sources (e.g. shock tube data, plasma torches, etc.). In the second mode, NEQAIR v15.0 is used as a radiative heat flux prediction tool for flight projects. Correspondingly, NEQAIR has also been used to simulate the radiance measured on previous flight missions. This report summarizes the database updates, corrections that have been made to the code, changes to input files, parallelization, the current usage recommendations, including test cases, and an indication of the performance enhancements achieved.

Description: No abstract available

Description: A validated computational fluid-structure interaction method for simulating the complex interaction between the large deformation of very thin, highly deformable structures and compressible flows is extended to consider large-scale problems in supersonic flows using parallel computing. The coupled fluid-structure interaction system is solved in a partitioned, or weakly-coupled, manner. The foundations of the applied fluid-structure interaction method are a higher-order, block-structured Cartesian, sharp immersed boundary method for the compressible Navier-Stokes equations and a computational structural dynamics solver employing a geometrically nonlinear 3-node shell element based on the mixed interpolation of tensorial components formulation. The method is applied to large deformation fluid-structure interaction validation cases before being applied to the inflation of a supersonic parachute in the upper Martian atmosphere where the goal is to demonstrate the capabilities of the solver when considering large-scale problems in supersonic flows.

Description: The Mars Science Laboratory (MSL) was protected during entry into the Martian atmosphere by a thermal protection system that used NASAs Phenolic Impregnated Carbon Ablator (PICA). The heat shield of the probe was instrumented with the Mars Entry Descent and Landing Instrument (MEDLI) suite of sensors. MEDLI Integrated Sensor Plugs (MISP) included thermocouples that measured in-depth temperatures at various locations on the heatshield. The flight data has been used as a benchmark for validating ablation codes within NASA. This work seeks to refine the estimate of the material properties for the MSL heat shield and the aerothermal environment during Mars entry using estimation methods in DAKOTA on the temperature data obtained from MEDLI.

Description: No abstract available

Description: No abstract available

Description: The high power density of emerging electronic devices is driving the transition from remote cooling, which relies on conduction and spreading, to embedded cooling, which extracts dissipated heat on-site. Two-phase microgap coolers employ the forced flow of dielectric fluids undergoing phase change in a heated channel within or between devices. Such coolers must work reliably in all orientations for a variety of applications (e.g., vehicle-based equipment), as well as in microgravity and high-g for aerospace applications, but the lack of acceptable models and correlations for orientation- and gravity-independent operation has limited their use. Reliable criteria for achieving orientation- and gravity-independent flow boiling would enable emerging systems to exploit this thermal management technique and streamline the technology development process. As a first step toward understanding the effect of gravity in two-phase microgap flow and transport, in an earlier effort, the authors studied the effects of evaporator orientation, mass flux, and heat flux on flow boiling of HFE7100 in a 1.01 mm tall by 13.0 mm wide by 12.7 mm long microgap channel. Orientation-independence, defined as achieving similar critical heat fluxes, heat transfer coefficients, and flow regimes across orientations, was achieved for mass fluxes of 400 kg/sq.m-s and greater (corresponding to a Froude number of about 0.8). In the present effort, the authors have studied the effects of gravity, mass flux, and subcooling on flow boiling of HFE7100 in a 0.17 mm tall by 13.0 mm wide by 12.7 mm long microgap channel. The Flow Boiling in Microgap Coolers payload experienced about three minutes of weightlessness and shorter periods of high-g (up to about 5 g) during two recent flights aboard the Blue Origin New Shepard reusable launch vehicle. The results from the flight experiments will be presented and compared with published criteria for achieving gravity-independence.

Description: An infrared (IR) camera provides a way of examining temperature trends associated with simulated microgravity flame spread in the Narrow Channel Apparatus (NCA). The IR camera measures the surface temperature of solid poly methyl methacrylate (PMMA) fuel. These tests examine the forward conduction of heat ahead of the flame front in the non-thermally thin fuel.The NCA is a combustion wind tunnel that simulates a microgravity flame spread environment by employing a narrow gap between the fuel and ceiling of the device, limiting the effects of buoyancy. Test conditions of a 5 mm gap, mean opposed flow velocity of 15 cm/s, and fuel thickness of 3 mm are used.PMMA is selected as the fuel due to repeatability of test results, ease of computational modeling, and known combustion mechanics. Using specific lens and bandpass filter combinations the PMMA can be imaged as effectively opaque. The spectral emissivity for PMMA was calculated and incorporated into the calibration of the camera.Surface temperatures from the IR camera are compared to results from thermocouples embedded in the surface of the fuel. The IR camera results show that nontrivial forward conduction occurs during tests, and therefore must be included in computational models of the process.

Description: An efficient strategy for propagating sonic boom signatures from a near-field Computational Fluid Dynamics (CFD) solution to the mid-field is presented. The method is based on a high-order accurate finite-difference discretization of the 3D Euler equations on a specially designed curvilinear grid and a single sweep space marching solution algorithm. The new approach leads to more than a factor of two reduction in overall computational resources compared to the current method used to propagate near-field sonic booms to the ground. Accuracy and efficiency of the near-field to mid-field process is demonstrated using a selection of test cases from the AIAA Sonic Boom Prediction Workshops. Azimuthal dependence of nonlinear wave propagation from the near-field to mid-field is analyzed along with its effects on the ground level noise.

Description: Detailed spectrally and spatially resolved radiance has been measured in the Electric Arc Shock Tube at NASA Ames Research Center for conditions relevant to Titan entry, with varying atmospheric composition, free-stream density (equivalently, altitude) and shock velocity. The test campaign measured radiation at velocities from 4.7 km/s to 8 km/s and free-stream pressures of 0.1, 0.28 and 0.47 Torr with a variety of compositions. Radiances measured in this work are substantially larger compared to that reported both in past EAST test campaigns and in other shock tube facilities. Depending on the metric used for comparison, the discrepancy can be as high as an order of magnitude. Due to the difference with previously reported data, a substantial effort was undertaken to provide confidence in the new results. The present work provides a new benchmark set of data to replace those published in previous studies. The effect of gas impurities identified in previous shock tube studies was also examined by testing in pure N2 and deliberate addition of air to the CH4/N2 mixtures. Furthermore, a test campaign in pure N2 was also conducted with the aim of providing data for improving fundamental understanding of high enthalpy flows containing N2, such as high-speed entries into Earth or Titan. These experiments cover conditions from approximately 6 km/s to 11 km/s at an initial pressure of 0.2 Torr. It is the intention of this paper to motivate code comparisons benchmarked against this data set.

Description: Modifications to key coefficients in a k E based explicit algebraic stress model (EASM) are examined with the objective of improving the prediction of turbulent jet flows. The pressure strain coefficient, C2 and the turbulent diffusion coefficients, k and E were investigated. For a series of benchmark subsonic jets at heated and unheated conditions, lowering C2 from the default value of 0.36 to 0.10 resulted in a significant improvement in the jet mixing, when compared to experimental data. Changing k and E from default values of 1.00 and 1.4489, respectively, to 0.50 and 0.7244, respectively, improved the initial mixing rate, while reducing the farfield mixing rate and the peak turbulent kinetic energy along the centerline. A high-speed mixing layer was also investigated for performance of baseline and modified EASM coefficients, with similar results as for the jet cases. A flat plate boundary layer was briefly examined to determine the effects of changing the coefficients on the turbulent skin friction coefficient. The change to the pressure strain coefficient, C2 = 0.10 is recommended for future EASM calculation of jets flow; however, it is also recommended that the diffusion coefficients remain at their default values.

Description: Two full seven-equation turbulence models available in the FUN3D code are evaluated for their ability to improve the computation of challenging mixing flows encountered in aerospace propulsion. These models are the SSG/LRR and Wilcox full second-moment Reynolds stress models. They solve equations for the six components of the Reynolds stress and a seventh equation for the turbulent length scale. Two standard eddy viscosity models are also evaluated for comparison, the Spalart-Allmaras (SA) one-equation model and the Menter Shear Stress Transport (SST-V) two-equation turbulence model. Flow through an axisymmetric reference nozzle is examined at three flow conditions: subsonic unheated, subsonic heated, and near sonic unheated. Centerline profiles of velocity and turbulent kinetic energy and radial profiles of velocity, turbulent kinetic energy and turbulent stresses are examined. Results showed that the SA model did well at predicting the jet potential core length, but over-mixed the downstream flow, whereas the SST-V model over-predicted the potential core length. The Wilcox-model significantly over-predicted the potential core length and under-predicted the mixing and was not well-suited for the jet flows evaluated, however the SSG/LRR Reynolds stress model did well at predicting the mixing rate and mean velocity for all cases examined.

Description: Film cooling is used in a wide variety of engineering applications for protection of surfaces from hot or combusting gases. The design of more efficient film cooling geometries/configurations could be facilitated by an ability to accurately model and predict the effectiveness of current designs using computational fluid dynamics (CFD) code predictions. Hence, a benchmark set of flow field property data were obtained for use in assessing current CFD capabilities and for development of better modeling approaches for these turbulent flow fields where accurate calculation of turbulent heat flux is important. Both Particle Image Velocimetry (PIV) and spontaneous rotational Raman scattering (SRS) spectroscopy were used to acquire high quality, spatially-resolved measurements of the mean velocity, turbulence intensity as well as the mean temperature and root mean square (rms) temperatures in a film cooling flow field. In addition to off-body flow field measurements, infrared thermography (IR) and thermocouple measurements on the plate surface enabled estimates of the film effectiveness. Raman spectra in air were obtained across a matrix of axial locations downstream from a 68.07 mm square nozzle blowing heated air over a range of temperatures (up to TR = 2.7) and Mach numbers (up to M0.9), across a 30.48 cm long plate equipped with three patches of 45 small (~1 mm) diameter cooling holes arranged in a staggered configuration. In addition, both centerline streamwise 2-component PIV and cross-stream 3-component Stereo PIV data at 14 axial stations were collected in the same flows. Only a subset of the data collected in the test program is included in this Part I report and are available from the NASA STI office. The final portion of the data will be published in a future report, Part II, along with CFD predictions of the complex cooling film flow.

Description: The two decades old high order central differencing via entropy splitting and summation-by-parts (SBP) difference boundary closure of Olsson & Oliger, Gerritsen & Olsson, and Yee et al. (15, 7, 37) is revisited. The objective of this paper is to prove for the first time that the entropy split scheme is an entropy stable method for central differencing with SBP operators for both periodic and non-periodic boundary conditions for nonlinear Euler equations. Standard high order spatial central differencing as well as high order central spatial DRP (dispersion relation preserving) spatial differencing is part of the entropy stable methodology framework. The proof is to replace the spatial derivatives by summation-by-parts (SBP) difference operators in the entropy split form of the equations using the physical entropy of the Euler equations. The numerical boundary closure follows directly from the SBP operator. No additional numerical boundary procedure is required. In contrast, Tadmor-type entropy conserving schemes (31) using mathematical entropies and more recently in (35], do not naturally come with a numerical boundary closure and a generalized SBP operator has to be developed (18). Long time integration of 2D and 3D test cases is included to show the comparison of this efficient entropy stable method with the Tadmor-type of entropy conservative methods. Studies also include the comparison among the three skew-symmetric splittings on their nonlinear stability and accuracy performance without added numerical dissipations for smooth flows. These are, namely, entropy splitting, Ducros et al. splitting and the Kennedy & Grubber splitting.

Description: Arc-jets are unique facilities used in research, development, and evaluation of high-temperature thermal protection systems for hypersonic vehicles and planetary entry systems. Thermochemical non-equilibrium computational fluid dynamics simulations have been carried out for the Hypersonic Materials Environmental Test System arc-jet facility to determine the size of a capsule model before arc-jet testing by better understanding of the physical phenomena. The results show the effect of the test article geometry and the importance of high-quality grids for accurate solutions. Accurate computational modeling of hypersonic flow fields inside arc-jets under simulated planetary entry conditions would help improve the design of thermal protection systems that may enable human exploration of the Moon, Mars, and beyond.

Description: A system and method for determining a change in a thickness and temperature of a surface of a material are disclosed herein. The system and the method are usable in a thermal protection system of a space vehicle, such as an aeroshell of a space vehicle. The system and method may incorporate micro electric sensors arranged in a ladder network and capacitor strip sensors. Corrosion or ablation causes a change in an electrical property of the sensors. An amount of or rate of the corrosion or the ablation and a temperature of the material is determined based on the change of the electrical property of the sensors.

Description: In this presentation, the theory and application of multi-layer insulation (MLI) behavior, with a specific focus on lower temperature applications (〈180K), is discussed. Many parameters can affect the performance of MLI (i.e. construction method, size, materials, grounding, penetrations, etc.) and these factors can make the prediction of MLI performance a challenge. Often, MLI performance is measured in terms of estar, and analysts commonly apply bias between a high and a low estar value. However, this approach can be dangerous when a mission goes through a wide range of temperatures during its lifetime (such as our mission, L'Ralph) due to temperature dependence of estar, with estar values increasing exponential as temperatures get colder. Many research papers and correlations have been published about MLI behavior, showing how estar values can rapidly rise at low temperatures. These correlations also show how the different parameters of MLI can affect and amplify this growth. Various correlations are presented as well as how L'Ralph is approaching the MLI problem. L'Ralph thermal model is built with Thermal Desktop (TD), and a discussion of how to apply the temperature dependent MLI behavior within TD is included. The presentation also includes reviews of different methods of mitigating heat leaks through MLI, touching briefly on topics such as integrated-MLI (IMLI), Dacron vs silk netting, and using multi-layered meshes to improve estar performance.

Description: A discussion of the impact of gravity on boiling and condensation phenomena especially related to space flight and the concept of gravity independence.

Description: This poster provides a glimpse of the aerothermal analysis and TPS design work for the Mars Sample Retrieval Lander (SRL), part of the Mars Sample Return (MSR) architecture.

Description: Author(s): Tao Liu, James Jun He, and Franco Nori (野理) Conventional n -dimensional topological superconductors (TSCs) have protected gapless ( n − 1 ) -dimensional boundary states. In contrast to this, second-order TSCs are characterized by topologically protected gapless ( n − 2 ) -dimensional states with the usual gapped ( n − 1 ) boundaries. Here, we study a second... [Phys. Rev. B 98, 245413] Published Thu Dec 13, 2018

Description: Author(s): Kai Wang, Haizhen Wu, Mengke Ge, Xingang Hou, Ning Liu, Jia He, Wei Xi, and Jun Luo It is well known that surface melting of metal materials is caused by vacancies, and melting proceeds layer by layer in theoretical predictions. However, the melting process has rarely been directly investigated in real time at atomic resolution. Herein, the (200) surface-melting process of Cu nanop... [Phys. Rev. B 98, 045425] Published Wed Jul 25, 2018

Description: Author(s): Neng Wang, Shubo Wang, Zhao-Qing Zhang, and C. T. Chan Using a multiple scattering technique, we derived closed-form expressions for effective constitutive parameters and electro/magneto-strictive tensor components for 2D bianisotropic metamaterials. Using the principle of virtual work, we obtained the electromagnetic stress tensor that can be used to c... [Phys. Rev. B 98, 045426] Published Wed Jul 25, 2018

Description: Author(s): Fan Yang, Loïc Henriet, Ariane Soret, and Karyn Le Hur We design a driven superconducting box with four spins S = 1 / 2 (qubits) such that coupled devices can give insight on the occurrence of quantum spin liquids and many-body Majorana states. Within one box or island, we introduce a generalized nuclear magnetic resonance algorithm to realize our models an... [Phys. Rev. B 98, 035431] Published Thu Jul 26, 2018

Description: Author(s): Andrew A. Allocca, Dmitry K. Efimkin, and Victor M. Galitski We examine excitons formed in the bulk of a topological insulator as the system is tuned via a parameter between topological and trivial insulating phases, arguing that nontrivial topology has fingerprints in the spectrum of these excitons. The closely related hydrogen atom problem is well known to ... [Phys. Rev. B 98, 045430] Published Fri Jul 27, 2018

Description: Author(s): Burak Özdamar, Gözde Özbal, M. Neşet Çınar, Koray Sevim, Gizem Kurt, Birnur Kaya, and Hâldun Sevinçli Using first-principles density functional theory calculations, we investigate a family of stable two-dimensional crystals with chemical formula A 2 B 2 , where A and B belong to groups IV and V, respectively ( A = C , Si, Ge, Sn, Pb; B = N , P, As, Sb, Bi). Two structural symmetries of hexagonal lattices P 6 ¯ m 2 ... [Phys. Rev. B 98, 045431] Published Fri Jul 27, 2018

Description: Author(s): Babatunde M. Ayeni, Robert N. C. Pfeifer, and Gavin K. Brennen Non-Abelian anyons can exist as pointlike particles in two-dimensional systems and have particle exchange statistics which are neither bosonic nor fermionic. Like in spin systems, the role of fusion (Heisenberg-like) interactions between anyons has been well studied. However, unlike our understandin... [Phys. Rev. B 98, 045432] Published Mon Jul 30, 2018

Description: Author(s): F. Pawlicki and I. Weymann The Andreev transport through a large-spin magnetic molecule, such as a single molecular magnet, attached to superconducting and ferromagnetic leads is studied theoretically by means of the real-time diagrammatic technique. It is shown that due to the proximity effect, molecular Andreev bound states... [Phys. Rev. B 98, 085411] Published Tue Aug 07, 2018

Description: Author(s): Valentin N. Popov It has been long accepted that the second-order Raman bands in carbon nanotubes are enhanced through the double-resonance mechanism. Although separate aspects of this mechanism have been studied for a few second-order Raman bands, including the most intense defect-induced D band and the two-phonon 2... [Phys. Rev. B 98, 085413] Published Tue Aug 07, 2018

Description: Author(s): Luis M. Canonico, Jose H. García, Tatiana G. Rappoport, Aires Ferreira, and R. B. Muniz The Haldane model on a honeycomb lattice is a paradigmatic example of a system featuring quantized Hall conductivity in the absence of an external magnetic field, that is, a quantum anomalous Hall effect. Recent theoretical work predicted that the anomalous Hall conductivity of massive Dirac fermion... [Phys. Rev. B 98, 085409] Published Mon Aug 06, 2018

Description: Author(s): F. Reyes Gómez, N. Porras-Montenegro, Osvaldo N. Oliveira, Jr., and J. R. Mejía-Salazar Self-similar bulk plasmon-polariton modes in quasiperiodic photonic superlattices were used here for a giant enhancement of second harmonic generation. Results for Fibonacci and Thue-Morse-like superlattices indicate that not only the disorder but also the symmetry of the unit cell plays a crucial r... [Phys. Rev. B 98, 075406] Published Tue Aug 07, 2018

Description: Author(s): Norberto D. Lanzillotti-Kimura, Kevin P. O’Brien, Junsuk Rho, Haim Suchowski, Xiaobo Yin, and Xiang Zhang Acoustic vibrations at the nanoscale (GHz-THz frequencies) and their interactions with electrons, photons, and other excitations are the heart of an emerging field in physics: nanophononics. The design of ultrahigh frequency acoustic-phonon transducers, with tunable frequency, and easy to integrate ... [Phys. Rev. B 97, 235403] Published Mon Jun 04, 2018

Description: Author(s): Tao Hu, Fanhao Jia, Guodong Zhao, Jiongyao Wu, Alessandro Stroppa, and Wei Ren Transition-metal dichalcogenides (TMDs) monolayers have been considered as important two-dimensional semiconductor materials for the study of fundamental physics in the field of spintronics. However, the out-of-plane mirror symmetry in TMDs may constrain electrons' degrees of freedom and it may limi... [Phys. Rev. B 97, 235404] Published Mon Jun 04, 2018

Description: Author(s): Rifat Ferdous, Kok W. Chan, Menno Veldhorst, J. C. C. Hwang, C. H. Yang, Harshad Sahasrabudhe, Gerhard Klimeck, Andrea Morello, Andrew S. Dzurak, and Rajib Rahman We identify the presence of monatomic steps at the Si/SiGe or Si / SiO 2 interface as a dominant source of variations in the dephasing time of silicon (Si) quantum dot (QD) spin qubits. First, using atomistic tight-binding calculations we show that the g -factors and their Stark shifts undergo variation... [Phys. Rev. B 97, 241401(R)] Published Mon Jun 04, 2018

Description: Author(s): Motohiko Ezawa We propose second-order topological insulators (SOTIs) whose lattice structure has a hexagonal symmetry C 6 . We start with a three-dimensional weak topological insulator constructed on a stacked triangular lattice, which has only side topological surface states. We then introduce an additional mass t... [Phys. Rev. B 97, 241402(R)] Published Mon Jun 04, 2018

Description: Author(s): Kyung-Han Kim and Hyun-Woo Lee An ideal 1 H phase monolayer MoS 2 has mirror reflection symmetry, but this symmetry is broken in common experimental situations, where the monolayer is placed on a substrate. By using k · p perturbation theory, we investigate the effect of mirror symmetry breaking on the Berry curvature of the material... [Phys. Rev. B 97, 235423] Published Fri Jun 15, 2018

Description: Author(s): Dmitry K. Efimkin and Allan H. MacDonald In previous work, we have argued that the optical properties of moderately doped two-dimensional semiconductors can be described in terms of excitons dressed by their interactions with a degenerate Fermi sea of additional charge carriers. These interactions split the bare exciton into attractive and... [Phys. Rev. B 97, 235432] Published Thu Jun 21, 2018

Description: Author(s): Yong Zhong, Sha Han, Yang Wang, Zhiling Luo, Ding Zhang, Lili Wang, Wei Li, Ke He, Can-Li Song, Xu-Cun Ma, and Qi-Kun Xue We report the atomic-scale structure of epitaxial films of the parent infinite-layer compound SrCu O 2 prepared on SrTiO 3 by molecular beam epitaxy. In situ scanning tunneling microscopy study reveals a stoichiometric copper oxide ( CuO 2 ) -terminated surface featured by 2 × 2 reconstruction, caused prima... [Phys. Rev. B 97, 245420] Published Fri Jun 22, 2018

Description: Author(s): S. S. Krishtopenko, S. Ruffenach, F. Gonzalez-Posada, G. Boissier, M. Marcinkiewicz, M. A. Fadeev, A. M. Kadykov, V. V. Rumyantsev, S. V. Morozov, V. I. Gavrilenko, C. Consejo, W. Desrat, B. Jouault, W. Knap, E. Tournié, and F. Teppe We report on temperature-dependent terahertz spectroscopy of a three-layer InAs/GaSb/InAs quantum well (QW) with inverted-band structure. The interband optical transitions, measured up to 16 T at different temperatures by Landau-level magnetospectroscopy, demonstrate the inverted-band structure of t... [Phys. Rev. B 97, 245419] Published Fri Jun 22, 2018

Description: Author(s): Michael A. Lively, Samuel X. Bennett, and Jean Paul Allain The use of energetic ion beams to induce nanopattern formation at surfaces has been well studied both experimentally and theoretically. However, the influence on morphological evolution of the implanted species themselves remains little understood, particularly in the case when the incident ion spec... [Phys. Rev. B 97, 235443] Published Tue Jun 26, 2018

Description: Author(s): Michele Tamagnone, Tetiana M. Slipchenko, Clara Moldovan, Peter Q. Liu, Alba Centeno, Hamed Hasani, Amaia Zurutuza, Adrian M. Ionescu, Luis Martin-Moreno, Jérôme Faist, Juan R. Mosig, Alexey B. Kuzmenko, and Jean-Marie Poumirol Faraday rotation is a fundamental property present in all nonreciprocal optical elements. In the THz range, graphene displays strong Faraday rotation; unfortunately, it is limited to frequencies below the cyclotron resonance. Here, we show experimentally that in specifically designed metasurfaces, m... [Phys. Rev. B 97, 241410(R)] Published Tue Jun 26, 2018

Description: Author(s): Manuel Hochheim and Thomas Bredow The electronic gap of bulk NaCl and the band-edge levels of the NaCl(100) surface are calculated using GW methods and self-consistent dielectric dependent hybrid functionals. Optical spectra are calculated by solving the Bethe-Salpeter equations (GW-BSE). For the calculation of the electronic struct... [Phys. Rev. B 97, 235447] Published Wed Jun 27, 2018

Description: Author(s): Krzysztof P. Wójcik and Ireneusz Weymann We examine the influence of the superconducting proximity effect on the transport properties of a T-shaped double quantum dot strongly coupled to two normal, nonmagnetic or ferromagnetic leads. We show that the two-stage Kondo screening may be suppressed or enhanced by the presence of pairing correl... [Phys. Rev. B 97, 235449] Published Wed Jun 27, 2018

Description: Author(s): Anne Le Cunuder, Artyom Petrosyan, George Palasantzas, Vitaly Svetovoy, and Sergio Ciliberto We present detailed measurements of the Casimir-Lifshitz force between two gold surfaces, performed in both gas (nitrogen) and liquid (ethanol) environments with the same apparatus and on the same spot of the sample. Furthermore, we study the role of double-layer forces in the liquid, and we show th... [Phys. Rev. B 98, 201408(R)] Published Wed Nov 28, 2018

Description: Author(s): A. Latief and B. Béri The topological Kondo effect arises when conduction electrons in metallic leads are coupled to a mesoscopic superconducting island with Majorana fermions. Working with its minimal setup, we study the lead electron local tunneling density of states in its thermally smeared form motivated by scanning ... [Phys. Rev. B 98, 205427] Published Wed Nov 28, 2018

Description: Author(s): Bo Hellsing, Thomas Frederiksen, Federico Mazzola, Thiagarajan Balasubramanian, and Justin W. Wells The linewidths of the π and σ bands originating from the electron-phonon coupling in graphene are analyzed based on model calculations and experimental angle-resolved photoemission spectroscopy (ARPES) data. We find evidence for crucial contributions to the lifetime broadening from interband scatter... [Phys. Rev. B 98, 205428] Published Thu Nov 29, 2018

Description: Author(s): Amany Raslan and W. A. Atkinson Multiple experiments have observed a sharp transition in the band structure of LaAlO 3 / SrTiO 3 (001) interfaces as a function of applied gate voltage. This Lifshitz transition, between a single occupied band at low electron density and multiple occupied bands at high density, is remarkable for its abr... [Phys. Rev. B 98, 195447] Published Fri Nov 30, 2018

Description: Author(s): Zhong-Qiu Fu, Yu Zhang, Jia-Bin Qiao, Dong-Lin Ma, Haiwen Liu, Zi-Han Guo, Yi-Cong Wei, Jing-Yi Hu, Qian Xiao, Xin-Rui Mao, and Lin He Understanding different approaches to confining massless Dirac fermions in graphene is of keen interest to researchers; it is also a central problem in making electronic devices based on graphene. Here, we studied spatial confinement, magnetic localization, and their interactions on massless Dirac f... [Phys. Rev. B 98, 241401(R)] Published Mon Dec 03, 2018

Description: Author(s): Peter Karlsen, Mikhail V. Shuba, Polina P. Kuzhir, Albert G. Nasibulin, Patrizia Lamberti, and Euan Hendry In recent years, there have been conflicting reports regarding the ultrafast photoconductive response of films of single walled carbon nanotubes (CNTs), which apparently exhibit photoconductivities that can differ even in sign. Here, we observe explicitly that the THz photoconductivity of CNT films ... [Phys. Rev. B 98, 241404(R)] Published Mon Dec 03, 2018

Description: Author(s): Jia-Bin Qiao, Long-Jing Yin, and Lin He Very recently, twisted graphene bilayers (TGBs) around the first magic angle θ ≈ 1 . 1 ∘ have attracted much attention for the realization of exotic quantum states, such as correlated insulator behavior and unconventional superconductivity. Here we elaborately study a series of TGBs around the first magi... [Phys. Rev. B 98, 235402] Published Mon Dec 03, 2018

Description: Author(s): S. Jafarpisheh, A. W. Cummings, K. Watanabe, T. Taniguchi, B. Beschoten, and C. Stampfer The weak intrinsic spin-orbit coupling in graphene can be greatly enhanced by proximity coupling. Here, we report on the proximity-induced spin-orbit coupling in graphene transferred by hexagonal boron nitride (hBN) onto the topological insulator Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 (BSTS) which was grown on a hBN ... [Phys. Rev. B 98, 241402(R)] Published Mon Dec 03, 2018

Description: Author(s): J. Schulenborg, J. Splettstoesser, and M. R. Wegewijs Open fermion systems with energy-independent bilinear coupling to a fermionic environment have been shown to obey a general duality relation [J. Schulenborg et al. , Phys. Rev. B 93 , 081411 (2016) ] which allows for a drastic simplification of time-evolution calculations. In the weak-coupling limit, ... [Phys. Rev. B 98, 235405] Published Tue Dec 04, 2018

Description: Author(s): Mingjian Wen, Stephen Carr, Shiang Fang, Efthimios Kaxiras, and Ellad B. Tadmor The structural relaxation of multilayer graphene is essential in describing the interesting electronic properties induced by intentional misalignment of successive layers, including the recently reported superconductivity in twisted bilayer graphene. This is difficult to accomplish without an accura... [Phys. Rev. B 98, 235404] Published Tue Dec 04, 2018

Description: Author(s): Jasmin Graf, Hannes Pfeifer, Florian Marquardt, and Silvia Viola Kusminskiy A unique feature of cavity optomagnonics is the possibility of coherently coupling light to spin excitations on top of magnetic textures. Here, the authors propose a cavity-optomagnonic system with a nonhomogeneous magnetic ground state, namely, a vortex in a magnetic microdisc. Using both analytical and computational methods, they study the cavity-enhanced coupling between optical whispering gallery modes and magnon modes, localized at the vortex. The results, both in terms of value and tunability of the coupling, point to the promise of engineered optomagnonic systems for quantum information platforms. [Phys. Rev. B 98, 241406(R)] Published Wed Dec 05, 2018

Description: Author(s): María Florencia Ludovico and Massimo Capone We study the relation between quantum pumping of charge and the work exchanged with the driving potentials in a strongly interacting ac -driven quantum dot. We work in the large-interaction limit and in the adiabatic pumping regime, and we develop a treatment that combines the time-dependent slave-bo... [Phys. Rev. B 98, 235409] Published Wed Dec 05, 2018

Description: Author(s): S. S. Seetharaman, B. Tremain, W. L. Barnes, and I. R. Hooper Electroinductive waves have emerged as an attractive solution for designing metamaterials that support backward propagating waves. Stacked metasurfaces etched with complementary split-ring resonators (CSRRs) have also been shown to exhibit a broadband negative dispersion. We demonstrate, through exp... [Phys. Rev. B 98, 235408] Published Wed Dec 05, 2018

Description: Author(s): Vera V. Vyborova, Oleg Lychkovskiy, and Alexey N. Rubtsov A translation invariant one-dimensional system of spinless fermions with a finite-range attraction experiences a quantum phase transition to a phase-separated state. While being a conventional Luttinger liquid for a small interaction strength, spinless fermions form a droplet with the size smaller t... [Phys. Rev. B 98, 235407] Published Wed Dec 05, 2018

Description: Author(s): D. Pérez Daroca, P. Roura-Bas, and A. A. Aligia The zero-bias anomaly at low temperatures, originated by the Kondo effect when an electric current flows through a system formed by a spin- 1 / 2 quantum dot and two metallic contacts is theoretically investigated. In particular, we compare the width of this anomaly 2 T NE with that of the Kondo resonanc... [Phys. Rev. B 98, 245406] Published Thu Dec 06, 2018

Description: Author(s): I. Meirzada, Y. Hovav, S. A. Wolf, and N. Bar-Gill Nitrogen vacancy (NV) centers in diamond have been identified over the past few years as promising systems for a variety of applications, ranging from quantum information science to magnetic sensing. This relies on the unique optical and spin properties of the negatively charged NV. Many of these ap... [Phys. Rev. B 98, 245411] Published Tue Dec 11, 2018

Description: Author(s): Yuantao Xie and J. J. Heremans Quantum phase coherence lengths were experimentally measured in nanolithographic wires to investigate the effects of wire length on quantum decoherence, which can be limited by mechanisms such as coupling to an external classical environment. The work demonstrates that device geometry and coupling t... [Phys. Rev. B 98, 035429] Published Tue Jul 24, 2018

Description: Author(s): Wei Cai, Ori Reinhardt, Ido Kaminer, and F. Javier García de Abajo Free electrons can efficiently absorb or emit plasmons excited in a thin conductor, giving rise to multiple energy peaks in the transmitted electron spectra separated by multiples of the plasmon energy. When the plasmons are chiral, this can also give rise to transfer of orbital angular momentum (OA... [Phys. Rev. B 98, 045424] Published Tue Jul 24, 2018

Description: Author(s): Wei-Tao Lu, Hong-Yu Tian, Hong-Mei Liu, Yun-Fang Li, and Wen Li We studied the spin and valley transports and magnetoresistance effect in a MoS 2 junction with a quantum well inserted between the gate voltage and the ferromagnetic MoS 2 , which can apply generally to other transition metal dichalcogenides with the same crystal structure. In the absence of a quantum... [Phys. Rev. B 98, 075405] Published Mon Aug 06, 2018