ALBERT

Description: The low-g fluids management group with the Center for Space Construction is engaged in active research on the following topics: gauging; venting; controlling contamination; sloshing; transfer; acquisition; and two-phase flow. Our basic understanding of each of these topics at present is inadequate to design space structures optimally. A brief report is presented on each topic showing the present status, recent accomplishings by our group and our plans for future research. Reports are presented in graphic and outline form.

Description: Experimental and theoretical studies have been conducted to determine critical parameters at the onset of nonlinear counterflow in He II below the lambda point of He-4. Critical temperature differences have been measured in porous media for zero net mass flow and for Darcy permeabilities in the order of magnitude range from 10 to the -10th to 10 to the -8th sq cm. The normalized critical temperature gradients, which covered the liquid temperature range of 1.5 K to the lambda temperature, are found to vary with T proportional to the ratio of the superfluid density to the normal fluid density. This liquid temperature dependence appears to be consistent with duct data which are limited at low temperature by a Reynolds number criterion.

Description: An analysis is made based upon the concept that the velocity fluctuations, and therefore, the Reynolds stresses, driven by the instability of the original flow grow until a new stable state is approached. The Reynolds stresses incorporated into the Orr-Sommerfeld equation are coupled with the main flow such that all the imaginary parts of the complex eigenvalues vanish, i.e., the original instability is eliminated. Using this stabilization principle, it is possible to find the Reynolds stresses as well as the mean velocity for plane Poiseuille flow with the Reynolds number slightly higher than the critical.

Description: The behavior of the reverse flow ceiling jet against the ventilation flow from 0.58 to 0.87 m/s was investigated in a 1/3 scale model of a wide body aircraft interior. For all tests, strong reverse-flow ceiling jets of hot gases were detected well upstream of the fire. Both thicknesses of the reverse-flow ceiling jet and the smoke layer increased with the fire-crossflow parameter. The thickness of the smoke layer where the smoke flows along the main flow below the reverse-flow ceiling jet was almost twice that of the reverse-flow ceiling jet. Detailed spatial and time-varying temperatures of the gas in the test section were measured, and velocity profiles were also measured using a temperature compensated hot film.

Description: Certain theoretical studies of boundary-layer transition are described, based on high Reynolds numbers and with attention drawn to the various nonlinear interactions and scales present. The article concentrates in particular on theories for which the mean-flow profile is completely altered from its original state. Two- and three-dimensional flow theory and conjectures on turbulent-boundary-layer structures are included. Specific recent findings noted, and in qualitative agreement with experiments, are: nonlinear finite-time break-ups in unsteady interactive boundary layers; strong vortex/wave interactions; and prediction of turbulent boundary-layer displacement- and stress sublayer-thicknesses.

Description: Three objectives are stated for activities at a proposed manned lunar base. One objective is scientific investigation of the moon and its environment and the application of special properties of the moon to research problems. Another objective would be to produce the capability of using the materials of the moon for beneficial purposes throughout the earth-moon system. The third objective is to conduct research and development leading to a self-sufficient and self-supporting lunar base, the first extraterrestrial human colony. The potential benefits to earth deriving from these moon-based activities, such as technology development and realization, as well as growing industrialization of near-earth space, are addressed.

Description: The evolutionary approach to space development is discussed in the framework of three overall strategies encompassing four case studies. The first strategy, human expeditions, places emphasis on highly visible, near-term manned missions to Mars or to one of the two moons of Mars. These expeditions are similar in scope and objectives to the Apollo program, with infrastructure development only conducted to the degree necessary to support one or two short-duration trips. Two such expeditionary scenarios, one to Phobus and the other to the Mars surface, are discussed. The second strategy involves the construction of science outposts, and emphasizes scientific exploration as well as investigation of technologies and operations needed for permanent habitation. A third strategy, evolutionary expansion, would explore and settle the inner solar system in a series of steps, with continued development of technologies, experience, and infrastructure.

Description: Nonequilibrium phenomena in hypersonic flows are examined on the basis of theoretical models and selected experimental data, in an introduction intended for second-year graduate students of aerospace engineering. Chapters are devoted to the physical nature of gas atoms and molecules, transitions of internal states, the formulation of the master equation of aerothermodynamics, the conservation equations, chemical reactions in CFD, the behavior of air flows in nonequilibrium, experimental aspects of nonequilibrium flow, a review of experimental results, and gas-solid interaction. Diagrams, graphs, and tables of numerical data are provided.

Description: Logistic difficulties associated with the Space Station Freedom are discussed. Proposed ground and on-orbit operations and procedures for supplying the Station are described. The transfer operations of supplies to the modules, the use of expendable launch vehicles for supplying the Station, and the use of EVA suits for assembling and servicing are considered. Ground support activities for resupplying and maintaining the spacecraft are examined.

Description: This paper presents the application of a class of multi-grid methods to the solution of the Navier-Stokes equations for two-dimensional laminar flow problems. The methods consists of combining the full approximation scheme-full multi-grid technique (FAS-FMG) with point-, line- or plane-relaxation routines for solving the Navier-Stokes equations in primitive variables. The performance of the multi-grid methods is compared to those of several single-grid methods. The results show that much faster convergence can be procured through the use of the multi-grid approach than through the various suggestions for improving single-grid methods. The importance of the choice of relaxation scheme for the multi-grid method is illustrated.

Description: Rapid distortion theory is applied to study distortion of homogeneous turbulence subject to two different axisymmetric strain modes: the axisymmetric contraction (AC, nozzle-type flow), and the axisymmetric expansion (AE, diffuser-type flow). The paper explores the differences in effects of the two axisymmetric strain modes on the anisotropy of correlations and structures of turbulence; examines the effect of dilatation on the distortion of turbulence; and provides a theoretical background for turbulence model development. It is found that velocity and vorticity fluctuations are enhanced more efficiently by contraction than by expansion; contraction produces much higher anisotropy in velocity and vorticity than expansion; root-mean-square pressure is slightly reduced during contraction, whereas it increases rapidly during expansion; and vortical structures of rodlike shape develop in a contraction flow, while disklike structures develop in an expansion flow. A simple model that reflects the dependence of turbulence evolution on structural parameters such as the Reynolds-stress anisotropy and total strain is proposed, and is shown to outperform all other models for all cases examined, regardless of the mean strain rate.

Description: A technique is described to estimate the area-to-mass ratio of debris fragments using orbital fragments obtained by radar. The area-to-mass ratio of about 2600 fragments arising from the breakup of 24 artificial satellites was determined; an analysis of the data on about 200 objects with known mass, size, and shape has been made, and a calibration of the observed radar cross-section (RCS) to the effective area of these objects has provided a method to estimate the effective area of debris fragments. From the knowledge of the effective area and the estimated area-to-mass ratio, the mass and area distribution of each of the known breakup has been obtained. As a function of time, the orbital elements can be used to invert any propagation algorithm to yield the area-to-mass ratio of an orbiting object.

Description: Plans for the Comet Rendezvous Asteroid Flyby (CRAF) mission are discussed. The CRAF spacecraft and mission configurations are illustrated and the scientific studies planned for the mission are listed. The scientific benefits of the study of comets and asteroids are reviewed and the characteristics of Comet Kopff are outlined. In addition, the structure, propulsion, attitude and articulation control, radio frequency and antenna, power and pyro, command, and data storage subsystems are described.

Description: Preliminary results from Voyager's encounter with Neptune are reviewed. The major events of the encounter are listed and the data on the atmosphere, magnetosphere, and ring-arc region of Neptune are discussed. The communications and photographical techniques used in the mission are examined. In addition, a search for Neptune satellites is considered.

Description: The NASA Space Shuttle Earth Observations Office conducts astronaut training in earth observations, provides orbital documentation for acquisition of data and catalogs, and analyzes the astronaut handheld photography upon the return of Space Shuttle missions. This paper provides backgrounds on these functions and outlines the data constraints, organization, formats, and modes of access within the public domain.

Description: The introduction of transverse velocity fluctuations into a separated shear layer on an airfoil at high angles of attack is presently demonstrated to be an effective separation-control technique. Airfoil aerodynamic characteristics, including poststall lift and drag as well as maximum lift coefficient and stall angle, all exhibited improvements controlled forcing at 20 deg angle of attack led to an increased spreading of the mean velocity profile, together with increased turbulence activity; separation moved from the leading edge to about 80 percent of chord.

Description: Numerical studies of turbulent flow in an axisymmetric 45-deg-expansion combustor and bifurcated diffuser are presented. The Navier-Stokes equations incorporating a k-epsilon model were solved in a nonorthogonal curvilinear coordinate system. A zonal-grid method, where the flow field was divided into several subsections, was developed. This approach permitted different computational schemes to be used in the various zones. In addition, grid generation was made a more simple task. Boundary overlap and interpolating techniques were used, and an adjustment of the flow variables was required to assure conservation of mass flux. Three finite-differencing methods (hybrid, quadratic upwind, and skew upwind) were used to represent the convection terms. Results were compared with existing experimental data. In general, good agreement between predicted and measured values was obtained.

Description: The old concept of using the wake of a spacecraft to obtain an ultrahigh vacuum is revisited. A wakeshield can be configured so that a surface of interest does not subtend any walls that could become contaminated, thus it should be possible to achieve a contamination-free, ultrahigh vacuum capability with infinite pumping speed even in the presence of high heat loads and moderate gas loads. This papar analyzes the conceptual design for a Space Ultravacuum Research Facility (SURF), both in a shuttle-attached mode and as a free flyer. It is shown that even in the shuttle-attached mode, it should be possible to obtain vacuum levels equivalent to 10 to the -9th to 10 to the -10th Torr with O and N2 as the primary constituents. As a free flyer the SURF will be limited primarily by the gas load from the process being performed. For chemical beam epitaxy it is shown that equivalent vacuum levels of 10 to the -14th Torr should be possible at 300 km.

Description: Rendezvous missions to earth-crossing asteroids are of interest to NASA, for scientific purposes as well as for technological applications and ecological implications. To provide a comprehensive data base for planners of such missions, a mission opportunity map (MOM) has been created for eight relatively easy-to-access asteroids. A MOM presents such mission data as launch dates, flight times, and launch and postlaunch delta V requirements for all useful mission opportunities. The merits of a MOM are: (1) searches for all useful mission oportunities are completed in the process of generating a MOM, and (2) a MOM provides a clear view of good and bad opportunities, the extent of performance variations, and the repeatability of the missions.

Description: To attain the fundamental goals of cometary exploration, rendezvous and sample return missions are necessary. This paper investigates various trajectory options and provides a comprehensive set of mission opportunities available for launches in the 1990s. The modes of explorations considered are rendezvous and flybys with atomized-sample-return missions. For each type of exploration, the paper describes various classes and modes of trajectories available, their inherent characteristics, and the techniques of identifying useful trajectories. The energy requirement associated with these missions and the performance possibilities are provided.

Description: An extensive investigation of the ways to rendezvous with diverse groups of asteroids residing between 2.0 and 5.0 AU is made, and the extent of achievable missions using the STS upper-stage launch vehicles (IUS 2-Stage/Star-48 or NASA Centaur) is examined. With judicious use of earth, Mars, and Jupiter gravity assists, rendezvous with some asteroids in all regions of space is possible. It is also shown that the STS upper stages are capable of carrying out missions beyond a single rendezvous, namely with several flybys and/or multiple rendezvous.

Description: Preliminary analysis results have been obtained for tests conducted to ascertain whether a distinctive fragmentation 'signature' allows discrimination between launch vehicle upper stage destructions due to hypervelocity particle impacts and internal explosions. An account is presently given of factors controlling the damage pattern created by hypervelocity impacts, and an evaluation is made of the applicability of the simulation results obtained to actual upper stage destruction characterization.

Description: A numerical procedure in which the Navier-Stokes equations are discretized using tightly coupled discretizations of pressure derivatives and continuity equations is used here to extend the range of known terminal velocities of gaseous bubbles in liquids well beyond that in previous investigations. Computations performed for Reynolds numbers up to 2000 and Marangoni numbers up to 1000 show only a modest variation of the scaled bubble velocity between 0.16 and 0.5. The bubble velocity is influenced more by the Marangoni number than by the Reynolds number.

Description: A numerical analysis is performed on thermocapillary buoyancy convection induced by phase change in a liquid droplet. A finite-difference code is developed using an alternating-direction implicit (ADI) scheme. The intercoupling relation between thermocapillary force, buoyancy force, fluid property, heat transfer, and phase change, along with their effects on the induced flow patterns, are disclosed. The flow is classified into three types: thermocapillary, buoyancy, and combined convection. Among the three mechanisms, the combined convection simulates the experimental observations quite well, and the basic mechanism of the observed convection inside evaporating sessile drops is thus identified. It is disclosed that evaporation initiates unstable convection, while condensation always brings about a stable density distribution which eventually damps out all fluid disturbances. Another numerical model is presented to study the effect of boundary recession due to evaporation, and the 'peeling-off' effect (the removal of the surface layer of fluid by evaporation) is shown to be relevant.

Description: Two-dimensional solidification influenced by anisotropic heat conduction has been considered. The interfacial energy balance was derived to account for the heat transfer in one direction (x or y) depending on the temperature gradient in both the x and y directions. A parametric study was made to determine the effects of the Stefan number, aspect ratio, initial superheat, and thermal conductivity ratios on the solidification rate. Because of the imposed boundary conditions, the interface became skewed and sometimes was not a straight line between the interface position at the upper and lower adiabatic walls (spatially nonlinear along the height). This skewness depends on the thermal conductivity ratio k(yy)/k(yx). The nonlinearity of the interface is influenced by the solidification rate, aspect ratio, and k(yy/k(yx).

Description: In this paper, mission orbit considerations are addressed for using the Space Shuttle as a telescope platform for observing man-made orbital debris. Computer modeling of various electrooptical systems predicts that such a space-borne system will be able to detect particles as small as 1-mm diameter. The research is meant to support the development of debris- collision warning sensors through the acquisition of spatial distribution and spectral characteristics for debris and testing of detector combinations on a shuttle-borne telescopic experiment. The technique can also be applied to low-earth-orbit-debris environment monitoring systems. It is shown how the choice of mission orbit, season of launch, and time of day of launch may be employed to provide extended periods of favorable observing conditions.

Description: A multiple-time-scale turbulence model of a single point closure and a simplified split-spectrum method is presented. In the model, the effect of the ratio of the production rate to the dissipation rate on eddy viscosity is modeled by use of the multiple-time-scales and a variable partitioning of the turbulent kinetic energy spectrum. The concept of a variable partitioning of the turbulent kinetic energy spectrum and the rest of the model details are based on the previously reported algebraic stress turbulence model. Example problems considered include: a fully developed channel flow, a plane jet exhausting into a moving stream, a wall jet flow, and a weakly coupled wake-boundary layer interaction flow. The computational results compared favorably with those obtained by using the algebraic stress turbulence model as well as experimental data. The present turbulence model, as well as the algebraic stress turbulence model, yielded significantly improved computational results for the complex turbulent boundary layer flows, such as the wall jet flow and the wake boundary layer interaction flow, compared with available computational results obtained by using the standard kappa-epsilon turbulence model.

Description: The emission from a gray radiating medium is analyzed for transient cooling in surroundings at a low temperature. The medium is rectangular with no variations in the direction normal to the cross section. The integral equation for the transient temperature distribution is solved numerically using a two-dimensional Gaussian integration subroutine. The emissive ability for a rectangle at uniform temperature is compared with that for transient cooling where the temperature distribution of the region has reached a fully developed shape, as shown by a separation of variables solution. The two solutions provide the upper and lower bounds for the emittance of a rectangle during transient cooling. The emittances for various aspect ratios are presented as a function of the mean length of the rectangle and are compared with results for a plane layer and a cylinder.

Description: Calculations for n-decane drops evaporating in a spherical cluster surrounded by unvitiated ambient air at atmospheric pressure were performed using two previously proposed cluster models. Both cluster models predict that turbulent transport effects are more important in the case of small clusters. This is due to the smaller volume to surface ratio and thus to the greater transport of hot unvitiated gas to the drops in order to promote evaporation. The results obtained are compared with those of two turbulent models for each one of the 'trapping factors' and similarity models.

Description: The effects of critical layer nonlinearity are considered on spatially growing oblique instability waves on nominally two-dimensional shear layers between parallel streams. The analysis shows that three-dimensional effects cause nonlinearity to occur at much smaller amplitudes than it does in two-dimensional flows. The nonlinear instability wave amplitude is determined by an integro-differential equation with cubic type nonlinearity. The numerical solutions to this equation are worked out and discussed in some detail. The numerical solutions always end in a singularity at a finite downstream distance.

Description: The effects of critical-layer nonlinearity on spatially growing oblique instability waves on compressible shear layers between two parallel streams are considered. The analysis shows that mean temperature nonuniformities cause nonlinearity to occur at much smaller amplitudes than it does when the flow is isothermal. The nonlinear instability wave growth rate effects are described by an integrodifferential equation which bears some resemblance to the Landau equation, in that it involves a cubic-type nonlinearity. The numerical solutions to this equation are worked out and discussed in some detail. Inviscid solutions always end in a singularity at a finite downstream distance, but viscosity can eliminate this singularity for certain parameter ranges.

Description: Flow characteristics in the vicinity of the flap of a single-slotted airfoil are presented and analyzed. The flow remained attached over the model surfaces, except in the vicinity of the flap trailing edge where a small region of boundary-layer separation extended over the aft 7 percent of flap chord. The airfoil configuration was tested at a Mach number of 0.09 and a chord Reynolds number of 1.8 x 10 to the 6th in the NASA Ames Research Center 7- by 10-Foot Wind Tunnel. The flow was complicated by the presence of a strong, initially inviscid, jet, emanating from the slot between airfoil and flap, and a gradual merging of the main airfoil wake and flap suction-side boundary layer.

Description: A simulation is performed of a passive scalar field convected by a rapidly fluctuating velocity field whose correlation time approaches zero. By using a code proposed in a previous study (Chasnov et al., 1988), the turbulence spectrum of the passive temperature field in the conductive subrange is determined. A theoretical model is proposed which explains the result obtained by representing the transfer of scalar variance by an eddy conductivity, whose correlation time is limited by the correlation time of the velocity field.

Description: The microspacecraft is defined as a fully functional spacecraft whose mass is on the order of 10 kg or less. The results of a recent microspacecraft workshop are reviewed. The workshop concluded that microspacecraft are feasible and can be enabling for missions that require multiple simultaneous measurements displaced in position or very high mission delta-VSDIO-s. The paper includes discussions of science objectives and instruments as well as potential missions. Potential missions include a very close approach to the sun, determining the origin of gamma ray bursters and a search for gravity waves. Technology for microspacecraft is coming from the 'Lightsat' or small satellite community and developments sponsored by the SDIO. Concepts for microspacecraft power and telecommunications subsystems developed at the JPL are presented. Due to their small size, microspacecraft can be launched by traditional chemical rockets and also unconventional launchers such as electromagnetic launchers.

Description: Long's self-similar vortex is known to have two solutions for each supercritical value of the flow force. Each of those solutions is shown to have a double structure if the flow force is large. The inertial instabilities of one of those large-flow-force limit solutions are investigated, showing that they are related to the instabilities of the Bickley jet in one regime. However, the swirl in the vortex becomes important for long waves, very strongly modifying the sinuous and varicose, Bickley modes. The asymptotic results obtained agree well with the numerical solutions for the sinuous mode, but not for the varicose mode, the difficulty in the latter case being apparently due to mode jumping.

Description: Numerical techniques are developed to solve the Navier-Stokes equations for unsteady incompressible flow. The extension of the finite-difference Galerkin (FDG) method of Stephens et al. (1984) to the continuous-time case in two or three space dimensions is explained, and the numerical implementation of the method is discussed with particular attention to the staggered-MAC-grid primitive-variable discretization, the application of discrete mass balance to avoid problems inherent in FDG schemes, the direct interpretation of the FDG expansion variables as a discrete streamfunction, and a mass-balance approach to two-dimensional problems with throughflow or obstacles. Numerical results are presented graphically for the evolution of asymptotic steady flow in a driven cavity at Reynolds number 400, 1000, or 3200; good agreement with published experimental data is demonstrated, with accurate predictions of secondary-vortex formation from wall bubble recirculations at Reynolds number 1000.

Description: Flow-field measurements of unsteady turbulent flow downstream of a rotating spoked-wheel wake generator were performed in a short-duration light-piston tunnel, and the instantaneous-velocity data were phase averaged based on a signal synchronized with the bar-passing frequency. Mean axial velocities were found to agree well with those obtained from measurements behind a stationary cylinder and to be independent of both Reynolds and bar-passing Strouhal numbers. Reynolds stresses were found to be consistent with related cylinder-wake measurements, but were significantly higher than corresponding measurements obtained in large-scale research turbomachines. Phase-averaged triple velocity correlations were calculated from the digital velocity records, revealing the sign and the magnitude of skewness in the velocity probability density distributions for the two components.

Description: The bifurcation diagram corresponding to the Eckhaus stability curve has been constructed for the one-dimensional Swift-Hohenberg equation in a finite domain. Finite-amplitude solutions with particular spatial wavelength recover linear stability, as predicted by the Eckhaus curve, after a sequence of secondary bifurcations from the branch of solutions with this wavelength. No connectivity between the primary-solution branches is admissible if the stability predicted by this bifurcation diagram is to correspond to the prediction of the Eckhaus analysis. The Eckhaus curve does not exist if nonlinear couplings destroy this pattern. This is demonstrated by analysis of a coupled pair of Swift-Hohenberg equations.

Description: The effects of asymmetry in furnace temperature profile and pulling velocity on the crystal interface shape are demonstrated while neglecting the latent heat of solidification. It is seen that the furnace temperature profile may be varied in order to influence the shape of the melt-crystal interface. An exact thermal analysis is then performed on the Bridgman technique by including the latent heat of solidification as a source term. The exact temperature field required for yielding a flat melt-crystal interface is obtained. The earlier observation regarding the influence of furnace temperature profile on the interface shape is confirmed and a criterion for achieving a flat interface is obtained. Various furnace temperature profiles are selected and their corresponding melt-crystal interface results are presented.

Description: The paper presents launch vehicle and upper-stage options for application to lunar and interplanetary microspacecraft missions. Particular attention is given to the capabilities of Piggyback, small launch vehicles, and large launch vehicles. It is noted that Piggyback options on the Shuttle and expendable launch vehicles enable near-term earth-orbital missions and the potential for lunar and planetary missions if an electric-propulsion upper-stage is developed. Launch systems like the Space Shuttle could be used to launch large members of microspacecraft in 'constellation deployment' and 'shotgun' class missions to a variety of solar-system targets such as the sun, asteroids, comets, the moon, Mars, and Saturn.

Description: The transonic aspect of helicopter flow analysis is addressed. The equations of motion and their implementations are examined, and the computation of real rotor flows is considered. Nonlifting rotor flows, high-speed hover, high advance ratio lifting rotor flows, and strong blade/vortex interaction computations are discussed.

Description: Some of the basic finite-difference schemes that can be used to solve the nonlinear equations that describe unsteady inviscid and viscous transonic flow are reviewed. Numerical schemes for solving the unsteady Euler and Navier-Stokes, boundary-layer, and nonlinear potential equations are described. Emphasis is given to the elementary ideas used in constructing various numerical procedures, not specific details of any one procedure.

Description: The general configuration, development schedule, and capabilities of the NASA International Space Station are reviewed, with an emphasis on the possibilities for long-term measurements of high-energy cosmic and secondary radiation from the main Station spacecraft, coorbiting or polar-orbit platforms, or Station-supported GEO satellites. Also outlined are the organizational structure and the application procedures to be followed by potential users of the Station facilities. Diagrams and drawings are provided.

Description: Transient cooling by radiation is analyzed for a cylindrical region filled with axially flowing streams of drops that are becoming solidified. This is of interest for the dissipation of waste heat from orbiting power system in space. The drops absorb, emit, and scatter radiation, and the surroundings are at a lower uniform temperature. The radiative properties are assumed gray, and the scattering is isotropic. The radiating region is a two-phase mixture that remains at the melting temperature of the drops. Its temperature uniformity maintains a high emissive power as energy is lost. This is an advantage over a sensible heat radiator in which the temperature decreases, thereby reducing the emissive power. The results provide the axial length that remains two-phase and the fraction of energy dissipated within this length in which the emissive power has not decreased because of sensible cooling. It is also shown how the radial distribution of the axial velocity of the drops can be modified to increase this energy fraction.

Description: A number of successful applications of a spectral collocation method extended by a multi-domain patching technique are shown. The multi-domain technique can be used to improve resolution for problems with widely disparate scales, and to reduce the ill-conditioning of the spectral operators for problems in which a large number of points are required for distributed resolution. A new nonreflecting outflow boundary treatment for unsteady transition-to-turbulence simulations is also presented, which relies on the multi-domain technique. The role of multi-domain in improving the efficiency of such calculations is discussed.

Description: Spectral element methods are high-order weighted residual techniques based on spectral expansions of variables and geometry for the Navier-Stokes (NS) and transport equations. Here, practical aspects of these methods and their efficient implementation are examined, and several examples of flows in truly complex geometries are presented. The spectral element discretization for NS equations is introduced, and the convergence of the method is addressed. An efficient data management scheme is discussed in the context of parallel processing computations. The method is validated by comparing the spectral element solutions with the exact eigensolutions for the Orr-Sommerfeld equations in two and three dimensions. Computer-aided flow visualizations are presented for an impulsive flow past a sharp edge wedge. Three-dimensional states of channel flow disrupted by an array of cylindrical eddy promoters are studied, and the results of a direct simulation of the turbulent flow in a plane channel are presented.

Description: Plans for space-science experiments on the International Space Station (ISS) are reviewed, with a focus on biological and medical research with implications for manned missions to the moon and planets (in a scenario culminating in the establishment of a space colony by about the year 2018). Both applied biomedical research (determining the limits of human endurance in space and developing CELSS technology to extend them) and basic research (on the physiological response of plants and animals to the space environment) are discussed, and particular attention is given to the design and deployment schedule for the ISS biomedical hardware modules (Life Sciences Module, Centrifuge Module, and Variable-Gravity Research Facility). Also included are diagrams; drawings; photographs; and tables listing the individual experiments, their objectives, and the hardware required.

Description: NASA has instituted a plan for the definition of activities and resources required over the coming decade for the deepening of current understanding of anthropogenic orbital debris, and its effects on future mission operations. This understanding will be the basis of policy definition and policy implementation efforts. The most immediate requirement is the definition of the debris environment, with emphasis on data for debris sizes smaller than 4 cm. Systems-damage criteria and hypervelocity-impact theory will then be used to define the hazard to specific spacecraft.

Description: The albedo of upper-stage breakup debris is proposed as an accurate discriminator among the various possible causes of breakup, which encompass residual fuel explosions and hypervelocity particle impacts. The fragments from an impact are covered with a thin layer of soot deposited from the destruction of polymeric circuit boards, while pressure vessel explosion fragments can be expected to remain soot-free. Albedo also facilitates the interpretation of small-debris optical telescope measurements.

Description: A description of the Axial Flow Turbine Research Facility (AFTRF) being built at the Turbomachinery Laboratory of the Pennsylvania State University is presented. The purpose of the research to be performed in this facility is to obtain a better understanding of the rotor/stator interaction, three dimensional viscous flow field in nozzle and rotor blade passages, spanwise mixing and losses in these blade rows, transport of wake through rotor passage, and unsteady aerodynamics and heat transfer of rotor blade row. The experimental results will directly feed and support the analytical and the computational tool development. This large scale low speed facility is heavily instrumented with pressure and temperature probes and has provision for flow visualization and laser Doppler anemometer measurement. The facility design permits extensive use of the high frequency response instrumentation on the stationary vanes and more importantly on the rotating blades. Furthermore it facilitates detailed nozzle wake, rotor wake, and boundary layer surveys. The large size of the rig also has the advantage of operating at Reynolds numbers representative of the engine environment.

Description: A quasi-three-dimensional analysis has been developed for unsteady rotor-stator interaction in turbomachinery. The analysis solves the unsteady Euler or thin-layer Navier-Stokes equations in a body-fitted coordinate system. It accounts for the effects of rotation, radius change, and stress-surface thickness. The Baldwin-Lomax eddy-viscosity model is used for turbulent flows. The equations are integrated in time using an explicit four-stage Runge-Kutta scheme with a constant time step. Implicit residual smoothing is used to increase the stability limit of the time-accurate computations. The scheme is described, and stability and accuracy analyses are given.

Description: A 3-D model was developed for simulating multistage turbomachinery flows using supercomputers. This average passage flow model described the time averaged flow field within a typical passage of a bladed wheel within a multistage configuration. To date, a number of inviscid simulations were executed to assess the resolution capabilities of the model. Recently, the viscous terms associated with the average passage model were incorporated into the inviscid computer code along with an algebraic turbulence model. A simulation of a stage-and-one-half, low speed turbine was executed. The results of this simulation, including a comparison with experimental data, is discussed.

Description: The flight testing conducted over the past 10 years in the NASA laminar-flow control (LFC) will be reviewed. The LFC program was directed towards the most challenging technology application, the high supersonic speed transport. To place these recent experiences in perspective, earlier important flight tests will first be reviewed to recall the lessons learned at that time.

Description: Although most of the laminar flow airfoils recently developed at the NASA Langley Research Center were intended for general aviation applications, low-drag airfoils were designed for transonic speeds and wind tunnel performance tested. The objective was to extend the technology of laminar flow to higher Mach and Reynolds numbers and to swept leading edge wings representative of transport aircraft to achieve lower drag and significantly improved operation costs. This research involves stabilizing the laminar boundary layer through geometric shaping (Natural Laminar Flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (Laminar-Flow Control, LFC), either through discrete slots or perforated surface. Results show that extensive regions of laminar flow with large reductions in skin friction drag can be maintained through the application of passive NLF boundary-layer control technologies to unswept transonic wings. At even greater extent of laminar flow and reduction in the total drag level can be obtained on a swept supercritical airfoil with active boundary layer-control.

Description: Aerodynamic forces and moments for a slender wing-body configuration are summarized from an investigation in the Langley National Transonic Facility (NTF). The results include both longitudinal and lateral-directional aerodynamic properties as well as slideslip derivatives. Results were selected to emphasize Reynolds number effects at a transonic speed although some lower speed results are also presented for context. The data indicate nominal Reynolds number effects on the longitudinal aerodynamic coefficients and more pronounced effects for the lateral-directional aerodynamic coefficients. The Reynolds number sensitivities for the lateral-directional coefficients were limited to high angles of attack.

Description: An interactive, graphical proximity operations planning system was developed which allows on-site design of efficient, complex, multiburn maneuvers in the dynamic multispacecraft environment about the space station. Maneuvering takes place in, as well as out of, the orbital plane. The difficulty in planning such missions results from the unusual and counterintuitive character of relative orbital motion trajectories and complex operational constraints, which are both time varying and highly dependent on the mission scenario. This difficulty is greatly overcome by visualizing the relative trajectories and the relative constraints in an easily interpretable, graphical format, which provides the operator with immediate feedback on design actions. The display shows a perspective bird's-eye view of the space station and co-orbiting spacecraft on the background of the station's orbital plane. The operator has control over two modes of operation: (1) a viewing system mode, which enables him or her to explore the spatial situation about the space station and thus choose and frame in on areas of interest; and (2) a trajectory design mode, which allows the interactive editing of a series of way-points and maneuvering burns to obtain a trajectory which complies with all operational constraints. Through a graphical interactive process, the operator will continue to modify the trajectory design until all operational constraints are met. The effectiveness of this display format in complex trajectory design is presently being evaluated in an ongoing experimental program.

Description: The objective is to provide useful engineering formulations and to instill a modest degree of physical understanding of the phenomena governing convective aerodynamic heating at high flight speeds. Some physical insight is not only essential to the application of the information presented here, but also to the effective use of computer codes which may be available to the reader. Given first is a discussion of cold-wall, laminar boundary layer heating. A brief presentation of the complex boundary layer transition phenomenon follows. Next, cold-wall turbulent boundary layer heating is discussed. This topic is followed by a brief coverage of separated flow-region and shock-interaction heating. A review of heat protection methods follows, including the influence of mass addition on laminar and turbulent boundary layers. Next is a discussion of finite-difference computer codes and a comparison of some results from these codes. An extensive list of references is also provided from sources such as the various AIAA journals and NASA reports which are available in the open literature.

Description: A co-operative testing program is in progress between the Langley Research Center (NASA) and the National Aeronautical Establishment (NAE, Canada) to validate two different techniques of airfoil testing at transonic speeds. The procedure employed is to test the same airfoil model in the NAE two-dimensional tunnel and the Langley 0.3-m Transonic Cryogenic Tunnel (0.3-m TCT). The airfoil model used in testing was CAST-10-2/DOA-2 super-critical airfoil. The Langley 0.3-m TCT has a relatively small cross section of 13 in x 13 in, giving a (h/c) ratio of 1.44 for the same 9 in chord model. The approach employed in the 0.3-m TCT aims towards eliminating the wall effects by using active walls. The top and bottom walls are flexible. By changing the wall shapes during a test in an iterative manner, the wall interference effects are reduced. The method employed to change the wall shapes is the adaptive wall technique. The current test program provided an opportunity to validate the adaptive wall technique in the 0.3-m TCT. The relatively long chord airfoil represents a severe test case to test the efficacy of the adaptive wall technique under cryogenic conditions. The program also involved removal of side wall boundary-layer thus increasing the complexity of the wall adaptation technique. This paper deals with some salient results obtained regarding repeatability of test data and possible residual interference effects.

Description: A multiphase turbulence closure model is presented which employs one transport equation, namely the turbulence kinetic energy equation. The proposed form of this equation is different from the earlier formulations in some aspects. The power spectrum of the carrier fluid is divided into two regions, which interact in different ways and at different rates with the suspended particles as a function of the particle-eddy size ratio and density ratio. The length scale is described algebraically. A mass/time averaging procedure for the momentum and kinetic energy equations is adopted. The resulting turbulence correlations are modeled under less retrictive assumptions comparative to previous work. The closures for the momentum and kinetic energy equations are given. Comparisons of the predictions with experimental results on liquid-solid jet and gas-solid pipe flow show satisfactory agreement.

Description: Generally, two types of theory are used to describe the field equations for suspensions. The so-called postulated equations are based on the kinetic theory of mixtures, which logically should give reasonable equations for solutions. The basis for the use of such theory for suspensions is tenuous, though it at least gives a logical path for mathematical arguments. It has the disadvantage that it leads to a system of equations which is underdetermined, in a sense that can be made precise. On the other hand, the so-called averaging theory starts with a determined system, but the very process of averaging renders the resulting system underdetermined. A third type of theory is proposed in which the kinetic theory of gases is used to motivate continuum equations for the suspended particles. This entails an interpretation of the stress in the particles that is different from the usual one. Classical theory is used to describe the motion of the suspending medium. The result is a determined system for a dilute suspension. Extension of the theory to more concentrated systems is discussed.

Description: The Office of Exploration has established a process whereby all NASA field centers and other NASA Headquarters offices participate in the formulation and analysis of a wide range of mission strategies. These strategies were manifested into specific scenarios or candidate case studies. The case studies provided a systematic approach into analyzing each mission element. First, each case study must address several major themes and rationale including: national pride and international prestige, advancement of scientific knowledge, a catalyst for technology, economic benefits, space enterprise, international cooperation, and education and excellence. Second, the set of candidate case studies are formulated to encompass the technology requirement limits in the life sciences, launch capabilities, space transfer, automation, and robotics in space operations, power, and propulsion. The first set of reference case studies identify three major strategies: human expeditions, science outposts, and evolutionary expansion. During the past year, four case studies were examined to explore these strategies. The expeditionary missions include the Human Expedition to Phobos and Human Expedition to Mars case studies. The Lunar Observatory and Lunar Outpost to Early Mars Evolution case studies examined the later two strategies. This set of case studies established the framework to perform detailed mission analysis and system engineering to define a host of concepts and requirements for various space systems and advanced technologies. The details of each mission are described and, specifically, the results affecting the advanced technologies required to accomplish each mission scenario are presented.

Description: The nation's efforts to expand human presence and activity beyond Earth orbit into the solar system was given renewed emphasis in January of 1988 when the Presidential Directive on National Space Policy was signed into effect. The expansion of human presence into the solar system has particular significance, in that it defines long-range goals for NASA's future missions. To embark and achieve such ambitious ventures is a significant undertaking, particularly compared to past space activities. Missions to Mars, the Moon, and Phobos, as well as an observatory based on the dark side of the Moon are discussed.

Description: The two-dimensional (2-D) and three-dimensional Navier-Stokes equations are solved for flow over a NAE CAST-10 airfoil model. Recently developed finite-volume codes that apply a multistage time stepping scheme in conjunction with steady state acceleration techniques are used to solve the equations. Two-dimensional results are shown for flow conditions uncorrected and corrected for wind tunnel wall interference effects. Predicted surface pressures from 3-D simulations are compared with those from 2-D calculations. The focus of the 3-D computations is the influence of the sidewall boundary layers. Topological features of the 3-D flow fields are indicated. Lift and drag results are compared with experimental measurements.

Description: An experimental Adaptive Wall Test Section (AWTS) process is described. Comparisons of the ONERA T2 and the 0.3-m TCT (transonic cryogenic tunnel) AWTS data for the ONERA CAST-10 airfoil are presented. Most of the 0.3-m TCT data is new and preliminary and no sidewall boundary layer control is involved. No conclusions are given.

Description: The transonic airfoil CAST 10-2/DOA 2 was investigated in several major transonic wind tunnels at Reynolds numbers ranging from Re=1.3 x 10(exp 6) to 45 x 10(exp 6) at ambient and cryogenic temperature conditions. The main objective was to study the degree and extent of the effects of Reynolds number on both the airfoil aerodynamic characteristics and the interference effects of various model-wind-tunnel systems. The initial analysis of the CAST 10-2 airfoil results revealed appreciable real Reynolds number effects on this airfoil and showed that wall interference can be significantly affected by changes in Reynolds number thus appearing as true Reynolds number effects.

Description: The vaporization of a droplet, interacting with its neighbors in a non-dilute spray environment is examined as well as a vaporization scaling law established on the basis of a recently developed theory of renormalized droplet. The interacting droplet consists of a centrally located droplet and its vapor bubble which is surrounded by a cloud of droplets. The distribution of the droplets and the size of the cloud are characterized by a pair-distribution function. The vaporization of a droplet is retarded by the collective thermal quenching, the vapor concentration accumulated in the outer sphere, and by the limited percolative passages for mass, momentum and energy fluxes. The retardation is scaled by the local collective interaction parameters (group combustion number of renormalized droplet, droplet spacing, renormalization number and local ambient conditions). The numerical results of a selected case study reveal that the vaporization correction factor falls from unity monotonically as the group combustion number increases, and saturation is likely to occur when the group combustion number reaches 35 to 40 with interdroplet spacing of 7.5 diameters and an environment temperature of 500 K. The scaling law suggests that dense sprays can be classified into: (1) a diffusively dense cloud characterized by uniform thermal quenching in the cloud; (2) a stratified dense cloud characterized by a radial stratification in temperature by the differential thermal quenching of the cloud; or (3) a sharply dense cloud marked by fine structure in the quasi-droplet cloud and the corresponding variation in the correction factor due to the variation in the topological structure of the cloud characterized by a pair-distribution function of quasi-droplets.

Description: Hypersonic vehicles operate in a hostile aerothermal environment which has a significant impact on their aerothermostructural performance. Significant coupling occurs between the aerodynamic flow field, structural heat transfer, and structural response creating a multidisciplinary interaction. A long term goal of the Aerothermal Loads Branch at the NASA Langley Research Center is to develop a computational capability for integrated fluid, thermal and structural analysis of aerodynamically heated structures. The integrated analysis capability includes the coupling between the fluid and the structure which occurs primarily through the thermal response of the structure, because: (1) the surface temperature affects the external flow by changing the amount of energy absorbed by the structure, and (2) the temperature gradients in the structure result in structural deformations which alter the flow field and attendant surface pressures and heating rates. In the integrated analysis, a finite element method is used to solve: (1) the Navier-Stokes equations for the flow solution, (2) the energy equation of the structure for the temperature response, and (3) the equilibrium equations of the structure for the structural deformation and stresses.

Description: Wind tunnel wall interference assessment and correction (WIAC) concepts, applications, and typical results are discussed in terms of several nonlinear transonic codes and one panel method code developed for and being implemented at NASA-Langley. Contrasts between 2-D and 3-D transonic testing factors which affect WIAC procedures are illustrated using airfoil data from the 0.3 m Transonic Cryogenic Tunnel and Pathfinder 1 data from the National Transonic Facility. Initial results from the 3-D WIAC codes are encouraging; research on and implementation of WIAC concepts continue.

Description: The stability of compressible 2-D and 3-D boundary layers is reviewed. The stability of 2-D compressible flows differs from that of incompressible flows in two important features: There is more than one mode of instability contributing to the growth of disturbances in supersonic laminar boundary layers and the most unstable first mode wave is 3-D. Whereas viscosity has a destabilizing effect on incompressible flows, it is stabilizing for high supersonic Mach numbers. Whereas cooling stabilizes first mode waves, it destabilizes second mode waves. However, second order waves can be stabilized by suction and favorable pressure gradients. The influence of the nonparallelism on the spatial growth rate of disturbances is evaluated. The growth rate depends on the flow variable as well as the distance from the body. Floquet theory is used to investigate the subharmonic secondary instability.

Description: The treatment of turbulence effects on transonic shock/turbulent boundary layer interaction is addressed within the context of a triple deck approach valid for arbitrary practical Reynolds numbers between 1000 and 10 billion. The modeling of the eddy viscosity and basic turbulent boundary profile effects in each deck is examined in detail using Law-of-the-Wall/Law-of-the-Wake concepts as the foundation. Results of parametric studies showing how each of these turbulence model aspects influences typical interaction zone property distributions (wall pressure, displacement thickness and local skin friction) are presented and discussed.

Description: The aerodynamic characteristics for both single and twin-engine high-performance aircraft are significantly affected by shock induced flow interactions as well as other local flow interference effects which usually occur at transonic speeds. These adverse interactions can not only cause high drag, but also cause unusual aerodynamic loadings and/or severe stability and control problems. Many programs are under way to not only develop method for reducing the adverse effects, but also to develop an understanding of the basic flow conditions which are the primary contributors. It is anticipated that these programs will result in technologies which can reduce the aircraft cruise drag through improved integration as well as increase aircraft maneuverability through the application of thrust vectoring. Some of the primary integration problems for twin-engine aircraft at transonic speeds are identified, and several methods are demonstrated for reducing or eliminating the undersirable characteristics, while enhancing configuration effectiveness.

Description: Algorithms are described for the generation and adaptation of unstructured grids in two and three dimensions, as well as Euler solvers for unstructured grids. The main purpose is to demonstrate how unstructured grids may be employed advantageously for the economic simulation of both geometrically as well as physically complex flow fields.

Description: For many internal transonic flows of practical interest, some of the relevant nondimensional parameters typically are small enough that a perturbation scheme can be expected to give a useful level of numerical accuracy. A variety of steady and unsteady transonic channel and cascade flows is studied with the help of systematic perturbation methods which take advantage of this fact. Asymptotic representations are constructed for small changes in channel cross-section area, small flow deflection angles, small differences between the flow velocity and the sound speed, small amplitudes of imposed oscillations, and small reduced frequencies. Inside a channel the flow is nearly one-dimensional except in thin regions immediately downstream of a shock wave, at the channel entrance and exit, and near the channel throat. A study of two-dimensional cascade flow is extended to include a description of three-dimensional compressor-rotor flow which leads to analytical results except in thin edge regions which require numerical solution. For unsteady flow the qualitative nature of the shock-wave motion in a channel depends strongly on the orders of magnitude of the frequency and amplitude of impressed wall oscillations or fluctuations in back pressure. One example of supersonic flow is considered, for a channel with length large compared to its width, including the effect of separation bubbles and the possibility of self-sustained oscillations. The effect of viscosity on a weak shock wave in a channel is discussed.

Description: The 1980s may well be called the Euler era of applied aerodynamics. Computer codes based on discrete approximations of the Euler equations are now routinely used to obtain solutions of transonic flow problems in which the effects of entropy and vorticity production are significant. Such codes can even predict separation from a sharp edge, owing to the inclusion of artificial dissipation, intended to lend numerical stability to the calculation but at the same time enforcing the Kutta condition. One effect not correctly predictable by Euler codes is the separation from a smooth surface, and neither is viscous drag; for these some form of the Navier-Stokes equation is needed. It, therefore, comes as no surprise to observe that the Navier-Stokes has already begun before Euler solutions were fully exploited. Moreover, most numerical developments for the Euler equations are now constrained by the requirement that the techniques introduced, notably artificial dissipation, must not interfere with the new physics added when going from an Euler to a full Navier-Stokes approximation. In order to appreciate the contributions of Euler solvers to the understanding of transonic aerodynamics, it is useful to review the components of these computational tools. Space discretization, time- or pseudo-time marching and boundary procedures, the essential constituents are discussed. The subject of grid generation and grid adaptation to the solution are touched upon only where relevant. A list of unanswered questions and an outlook for the future are covered.

Description: The application of computational fluid dynamics (CFD) to fighter aircraft design and development is discussed. Methodology requirements for the aerodynamic design of fighter aircraft are briefly reviewed. The state-of-the-art of computational methods for transonic flows in the light of these requirements is assessed and the techniques found most adequate for the subject application are identified. Highlights from some proof-of-feasibility Euler and Navier-Stokes computations about a complete fighter aircraft configuration are presented. Finally, critical issues and opportunities for design application of CFD are discussed.

Description: A brief survey is given on the study of transonic shock/boundary layer effects in flight. Then the possibility of alleviating the adverse shock effects through passive shock control is discussed. A Swedish flight experiment on a swept wing attack aircraft is used to demonstrate how it is possible to reduce the extent of separated flow and increase the drag-rise Mach number significantly using a moderate amount of perforation of the surface.

Description: The capability of accurate nonlinear flow analysis of resonance systems is essential in many problems, including combustion instability. Classical numerical schemes are either too diffusive or too dispersive especially for transient problems. In the last few years, significant progress has been made in the numerical methods for flows with shocks. The objective was to assess advanced shock capturing schemes on transient flows. Several numerical schemes were tested including TVD, MUSCL, ENO, FCT, and Riemann Solver Godunov type schemes. A systematic assessment was performed on scalar transport, Burgers' and gas dynamic problems. Several shock capturing schemes are compared on fast transient resonant pipe flow problems. A system of 1-D nonlinear hyperbolic gas dynamics equations is solved to predict propagation of finite amplitude waves, the wave steepening, formation, propagation, and reflection of shocks for several hundred wave cycles. It is shown that high accuracy schemes can be used for direct, exact nonlinear analysis of combustion instability problems, preserving high harmonic energy content for long periods of time.

Description: An iterative method for wall interference assessment and/or correction is presented for transonic flow conditions in wind tunnels equipped with two component velocity measurements on a single interface. The iterative method does not require modeling of the test article and tunnel wall boundary conditions. Analytical proof for the convergence and stability of the iterative method is shown in the subsonic flow regime. The numerical solutions are given for both 2-D and axisymmetrical cases at transonic speeds with the application of global Mach number correction.

Description: An explicit multistage Runge-Kutta type of time-stepping scheme is used for solving transonic flow past a transport type wing/fuselage configuration. Solutions for both Euler and Navier-Stokes equations are obtained for quantitative assessment of boundary layer interaction effects. The viscous solutions are obtained on both a medium resolution grid of approximately 270,000 points and a find grid of 460,000 points to assess the effects of grid density on the solution. Computed pressure distributions are compared with the experimental data.

Description: Some considerations toward developing numerical procedures for simulating viscous compressible flows are discussed. Both Navier-Stokes and boundary layer field methods are considered. Because efficient viscous-inviscid interaction methods have been difficult to extend to complex 3-D flow simulations, Navier-Stokes procedures are more frequently being utilized even though they require considerably more work per grid point. It would seem a mistake, however, not to make use of the more efficient approximate methods in those regions in which they are clearly valid. Ideally, a general purpose compressible flow solver that can optionally take advantage of approximate solution methods would suffice, both to improve accuracy and efficiency. Some potentially useful steps toward this goal are described: a generalized 3-D boundary layer formulation and the fortified Navier-Stokes procedure.

Description: An intense research effort over the last few years has produced several competing and apparently diverse methods for generating meshes. Recent progress is reviewed and the central themes are emphasized which form a solid foundation for future developments in mesh generation.