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  • 1
    Electronic Resource
    Electronic Resource
    Detailed simulation of nitrogen dissociation in stagnation regions (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 2108-2117 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vibrational relaxation rates from Schwartz–Slawsky–Herzfeld theory and the forced-harmonic oscillator model are used to study the flow of nitrogen in the stagnation region of a blunt body. The mass conservation equations are coupled to the momentum and total energy equations, and solved using an implicit finite-volume computational fluid dynamics method. The effects of single- and multiple-quantum vibration–translation transitions and vibration–vibration transitions are studied. Also, the effect of the mass diffusion of the excited oscillators across the shock layer is investigated. It is found that highly non-Boltzmann vibrational distributions are present in the flow field, and that the forced-harmonic oscillator model predicts that dissociation occurs from the low vibrational levels only. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869330
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  • 2
    Electronic Resource
    Electronic Resource
    Vibrational energy conservation with vibration–dissociation coupling: General theory and numerical studies (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 1764-1774 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The coupling between vibrational relaxation and dissociation in nitrogen is studied. The conservation of vibrational energy equation is derived and the form of the source terms is determined for physically consistent coupling models. Using a computational fluid dynamics method, the results from three current coupling models are compared to existing experimental interferograms for spherical geometries. It is found that the coupling models of Park, Treanor and Marrone, and Macheret and Rich are able to accurately predict the shock standoff distances and reproduce the experimental interference patterns for these conditions. However, there are differences in the vibrational temperature profiles among the coupling models. The experimental interferograms are not sensitive to these differences, though. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868491
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  • 3
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    Vibrational energy conservation with vibration–dissociation coupling: General theory and numerical studies (1995)
    American Institute of Physics
    Details
    Publication Date: 1995-07-01
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics
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  • 4
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    Detailed simulation of nitrogen dissociation in stagnation regions (1997)
    American Institute of Physics
    Details
    Publication Date: 1997-07-01
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics
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  • 5
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    Numerical study of inviscid shock interactions on double-wedge geometries (1997)
    Cambridge University Press
    Details
    Publication Date: 1997-12-10
    Description: Computational fluid dynamics has been used to study inviscid shock interactions on double-wedge geometries with the purpose of understanding the fundamental gas dynamics of these interactions. The parameter space of the interactions has been explored and the different types of interactions that occur have been identified. Although the interactions are produced by a different geometry, all but one of them may be identified as an Edney Type I, IV, V, or VI interaction. The previously unidentified interaction occurs because of the geometrical constraints imposed by the double wedge. The physical mechanisms for transition have been studied, and the transition criteria have been identified. An important result is that there are two different regimes of the parameter space in which the state of the flow downstream of the interaction point is fundamentally different. At high Mach numbers this flow is characterized by an underexpanded jet which impinges on the wedge and produces large-amplitude surface pressure variations. At low Mach numbers, the jet becomes a shear layer which no longer impinges on the wedge surface.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
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  • 6
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    Shock-Wave/Boundary-Layer Interactions in Hypersonic Low Density Flows (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Results of numerical simulations of Mach 10 air flow over a hollow cylinder-flare and a double-cone are presented where viscous effects are significant. The flow phenomena include shock-shock and shock- boundary-layer interactions with accompanying flow separation, recirculation, and reattachment. The purpose of this study is to promote an understanding of the fundamental gas dynamics resulting from such complex interactions and to clarify the requirements for meaningful simulations of such flows when using the direct simulation Monte Carlo (DSMC) method. Particular emphasis is placed on the sensitivity of computed results to grid resolution. Comparisons of the DSMC results for the hollow cylinder-flare (30 deg.) configuration are made with the results of experimental measurements conducted in the ONERA RSCh wind tunnel for heating, pressure, and the extent of separation. Agreement between computations and measurements for various quantities is good except that for pressure. For the same flow conditions, the double- cone geometry (25 deg.- 65 deg.) produces much stronger interactions, and these interactions are investigated numerically using both DSMC and Navier-Stokes codes. For the double-cone computations, a two orders of magnitude variation in free-stream density (with Reynolds numbers from 247 to 24,7 19) is investigated using both computational methods. For this range of flow conditions, the computational results are in qualitative agreement for the extent of separation with the DSMC method always predicting a smaller separation region. Results from the Navier-Stokes calculations suggest that the flow for the highest density double-cone case may be unsteady; however, the DSMC solution does not show evidence of unsteadiness.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 98-2668 , 7th AIAA/ASME Joint Thermophysics and Heat Transfer Conference; Jun 15, 1998 - Jun 18, 1998; Albuquerque, NM; United States
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  • 7
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    Measurement of Ultraviolet Radiative Heating Augmentation in HIEST Reflected Shock Tunnel (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-26
    Description: Radiance measurements in air at enthalpies from 8-20 MJkg have been made over a 250mm diameter flat-faced test article in Japan Aerospace Exploration Agency's HIgh-Enthalpy Shock Tunnel (HIEST). Measurements were made in the ultraviolet region (200-400 nm wavelength) in an attempt to resolve the long-standing discrepancy between theoryand measurements of heat flux over a blunt body; this discrepancy is often attributed toradiation. The spectra obtained indicate the presence of atomic iron vapor in the flowfield.At the highest enthalpies, the radiance is at the blackbody limit. An attempt to model theradiance is made by taking a nominal CFD flowfield without any contamination productsand processing it through a line-by-line radiation simulation tool. Iron vapor is introducedinto the shocked gas ahead of the model and radiation computations are repeated; the molefraction of iron vapor is adjusted to match the data. For the higher enthalpy conditions, theradiance was strongly absorbed and it was necessary to adjust the temperature and NOdensity in the freestream to match the signal below 300 nm. Once the observed spectrawere satisfactorily matched, the radiance to the stagnation point was then computed. It isshown that the impurity radiation is sufficiently large to explain the discrepancy.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: ARC-E-DAA-TN23557 , AIAA Thermophysics Conference; Jun 22, 2014 - Jun 26, 2014; Dallas, TX; United States
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  • 8
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    Preliminary Convective-Radiative Heating Environments for a Neptune Aerocapture Mission (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Convective and radiative heating environments have been computed for a three-dimensional ellipsled configuration which would perform an aerocapture maneuver at Neptune. This work was performed as part of a one-year Neptune aerocapture spacecraft systems study that also included analyses of trajectories, atmospheric modeling, aerodynamics, structural design, and other disciplines. Complementary heating analyses were conducted by separate teams using independent sets of aerothermodynamic modeling tools (i.e. Navier-Stokes and radiation transport codes). Environments were generated for a large 5.50 m length ellipsled and a small 2.88 m length ellipsled. Radiative heating was found to contribute up to 80% of the total heating rate at the ellipsled nose depending on the trajectory point. Good agreement between convective heating predictions from the two Navier-Stokes solvers was obtained. However, the radiation analysis revealed several uncertainties in the computational models employed in both sets of codes, as well as large differences between the predicted radiative heating rates.
    Keywords: Astrodynamics
    Type: AIAA Paper 2004-5177 , AIAA Atmospheric Flight Mechanics Conference and Exhibit; Aug 16, 2004 - Aug 19, 2004; Providence, RI; United States
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  • 9
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    Boundary Layer Transition and Trip Effectiveness on an Apollo Capsule in the JAXA High Enthalpy Shock Tunnel (HIEST) Facility (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Computational assessments were performed to size boundary layer trips for a scaled Apollo capsule model in the High Enthalpy Shock Tunnel (HIEST) facility at the JAXA Kakuda Space Center in Japan. For stagnation conditions between 2 MJ/kg and 20 MJ/kg and between 10 MPa and 60 MPa, the appropriate trips were determined to be between 0.2 mm and 1.3 mm high, which provided kappa/delta values on the heatshield from 0.15 to 2.25. The tripped configuration consisted of an insert with a series of diamond shaped trips along the heatshield downstream of the stagnation point. Surface heat flux measurements were obtained on a capsule with a 250 mm diameter, 6.4% scale model, and pressure measurements were taken at axial stations along the nozzle walls. At low enthalpy conditions, the computational predictions agree favorably to the test data along the heatshield centerline. However, agreement becomes less favorable as the enthalpy increases conditions. The measured surface heat flux on the heatshield from the HIEST facility was under-predicted by the computations in these cases. Both smooth and tripped configurations were tested for comparison, and a post-test computational analysis showed that kappa/delta values based on the as-measured stagnation conditions ranged between 0.5 and 1.2. Tripped configurations for both 0.6 mm and 0.8 mm trip heights were able to effectively trip the flow to fully turbulent for a range of freestream conditions.
    Keywords: Spacecraft Design, Testing and Performance; Fluid Mechanics and Thermodynamics
    Type: JSC-CN-32371
    Format: application/pdf
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  • 10
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    Aeroheating Measurement of Apollo Shaped Capsule with Boundary Layer Trip in the Free-piston Shock Tunnel HIEST (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An aeroheating measurement test campaign of an Apollo capsule model with laminar and turbulent boundary layer was performed in the free-piston shock tunnel HIEST at JAXA Kakuda Space Center. A 250mm-diameter 6.4%-scaled Apollo CM capsule model made of SUS-304 stainless steel was applied in this study. To measure heat flux distribution, the model was equipped with 88 miniature co-axial Chromel-Constantan thermocouples on the heat shield surface of the model. In order to promote boundary layer transition, a boundary layer trip insert with 13 "pizza-box" isolated roughness elements, which have 1.27mm square, were placed at 17mm below of the model geometric center. Three boundary layer trip inserts with roughness height of k=0.3mm, 0.6mm and 0.8mm were used to identify the appropriate height to induce transition. Heat flux records with or without roughness elements were obtained for model angles of attack 28 under stagnation enthalpy between H(sub 0)=3.5MJ/kg to 21MJ/kg and stagnation pressure between P(sub 0)=14MPa to 60MPa. Under the condition above, Reynolds number based on the model diameter was varied from 0.2 to 1.3 million. With roughness elements, boundary layer became fully turbulent less than H(sub 0)=9MJ/kg condition. However, boundary layer was still laminar over H(sub 0)=13MJ/kg condition even with the highest roughness elements. An additional experiment was also performed to correct unexpected heat flux augmentation observed over H(sub 0)=9MJ/kg condition.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: JSC-CN-30219 , AIAA Aerospace Sciences Meeting; Jan 13, 2013 - Jan 17, 2013; National Harbor, MD; United States
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