Giuliano Ranuzzi

Shock-Wave/Turbulent Boundary-Layer Interactions in Nonequilibrium Flows

Shock-wave/turbulent boundary-layer interactions in the presence of thermal and chemical nonequilibrium phenomena are analyzed. The approach relies on a linear eddy viscosity two-equation turbulence modeling that accounts for the coupling of turbulence with chemistry and vibration, and it employs a total variation diminishing e nite volume numerical methodology. The capability of the model has e rst been assessed for a cylinder e are cone guration, and results have been compared with experiments. The model has then been applied to assess the aerodynamic performance of control surfaces of a reusable launch vehicle. In particular, the effects of wall temperature and e ap dee ection on the separation, aerothermal loads, and e ap efe ciency have been studied. The analysisshowsthatturbulencebecomesimportantfore apdee ectionanglesgreaterthanacriticalvalue[ O (15deg)], thus avoiding thecrisis of thee ap efe ciency that is observed under laminarconditions and extending the operating capabilitiesofthecontrolsurface.Thestudy also showsthatthewalltemperatureaffectssignie cantly theefe ciency and the operating envelope of the e ap primarily under turbulent conditions.

Hypersonic Low-Density Aerothermodynamics of Orion-Like Exploration Vehicle

In the framework of Research Task Group 043 of the NATOResearch and Technology Organization, an analysis of the capabilities in prediction of aerothermal loads acting on a crew exploration vehicle at the higher altitudes of its reentry trajectory has been performed. In particular, the focus of this investigation is to provide information where overlap between the continuum approach (i.e., computational fluid dynamics) and particle approach (i.e., direct simulation Monte Carlo) occurs and improves understanding of relevant physics in transitional regime. Computational fluid dynamics calculations with slip flow boundary conditions had shown good predicting capabilities of slip velocity, slip temperature, and pressure, but not the surface heat flux. The analysis of the contributions to the total surface heat flux had exhibited the lack of continuum model in evaluating the convective heat flux in the transitional zone of the Orion reentry trajectory and an underestimation of shock wave thickness.

Evaluation of Local Effects of Transitional Knudsen Number on Shock Wave Boundary Layer Interactions

The influence of the local effects of rarefaction on the prediction of the main parameters typical of Shock Wave - Boundary Layer Interaction are presented and analyzed. Slip flow boundary conditions have been implemented in CIRA CFD code H3NS, and results have been compared with available wind tunnel experiments and DSMC results. Finally, an experimental wind tunnel test case, planned in CIRA Plasma Wind Tunnel facility, has been analyzed in order to check possible local effects of rarefaction.

Numerical and Experimental Analysis of Low-Density Effects in Suborbital Flight of FAST20XX

Subject of the present paper has been the experimental and numerical characterization of test chamber flow of DLR-V2G low-density wind tunnel, in the frame of EC FAST20XX project activities dedicated to the validation of numerical tools able to predict rarefaction effects in suborbital flight. Pitot pressure radial profiles measured at different positions downstream the test chamber have been compared at nozzle exit to numerical results obtained with different methodologies accounting for rarefaction effects (CFD with slip-flow boundary conditions, a hybrid CFD-DSMC procedure), and a re-definition of the V2G facility envelope in terms of flight-relevant parameters (Mach, Reynolds, Knudsen numbers) has been presented. A good agreement between experiments and numerical results has been achieved, thus confirming that the “actual” test chamber flow knowledge is of fundamental importance for a proper numerical rebuilding of an experimental test campaign.

Rarefied Aerothermodynamics Technology Development for Future High-Altitude High-Speed Transport (EU-FAST20XX)

First subject of the present paper has been the experimental and numerical characterization of test chamber flow of DLR-V2G low-density wind tunnel, in the frame of EU-FP7 FAST20XX project activities dedicated to the validation of numerical tools able to predict rarefaction effects in suborbital flight. Pitot pressure radial profiles measured at different positions downstream the test chamber have been compared at nozzle exit to numerical results obtained with different methodologies accounting for rarefaction effects (CFD with slip-flow boundary conditions, a hybrid CFD-DSMC procedure), and a re-definition of the V2G facility envelope in terms of flight-relevant parameters (Mach, Reynolds, Knudsen numbers) has been presented. A good agreement between experiments and numerical results has been achieved for M=12 and M=16 cases (not as good for M=22), thus confirming that the test chamber flow knowledge is of fundamental importance for a proper numerical rebuilding of an experimental test campaign. Further, the aerodynamic coefficients of lift, drag and pitching moment of the analyzed lifting body configuration have been experimentally determined by means of three component force and moment measurements in V2G and the influence of rarefaction onto the aerodynamic coefficients have been shown. The results have numerically been validated by means of DSMC calculations. After the validation of the numerical tools, the high altitude effects to the future hypersonic/suborbital re-entry vehicle SpaceLiner have been analyzed. Bridging functions have been developed and validated by means of DSMC calculations. The effects of rarefaction on global longitudinal aerodynamics of SpaceLiner in the range of altitude 65÷85 km have been pointed out by comparing to the aerodatabase in continuum regime conditions. DSMC computation has been done in the higher SpaceLiner altitude point confirming the bridging function results and providing heat transfer estimations. Two versions of SpaceLiner have been analyzed: SL4.3 and SL7.1.

Continuum and Kinetic Simulations of Orion (CEV) Atmospheric Re‐entry in High Altitude Flight Conditions

The high Knudsen number aerothermodynamics and the evaluation of effects of gas rarefaction in prediction of the main aero‐thermal loads of Crew Exploration Vehicle (CEV) is presented and analyzed. The focus of this investigation is to provide information where overlap between continuum approach and particle one occurs. It is well known that the Navier‐Stokes equations fail in rarefied regimes and a molecular approach such as the Direct Simulation Monte Carlo method (DSMC) is necessary. Slip flow boundary conditions have been implemented in CIRA CFD code H3NS in order to verify the extension of validity of a continuum method in the transition flow regime. Sensitivity of results to surface boundary conditions is presented.

Effects of the Surface Catalysis on High-Enthalpy Shock- Wave/Turbulent Boundary-Layer Interactions

In the present paper the effects of the surface catalysis on turbulent hypersonic flows dominated by shock-wave boundary-layer interactions over wing-flap configurations are analyzed. The approach relies on a linear eddy viscosity two-equation turbulence modeling that accounts for the coupling of turbulence with chemistry and vibration, and it employs a total variation diminishing finite volume numerical methodology. Two different catalysis models due to Kurotaki and Nasuti et al. have been implemented to account for the atomic oxygen and nitrogen recombination over silica-based surfaces. Several simulations have been carried out for sphere-cone and double-wedge configurations, and results have been compared with experiments. The effects of the surface catalytic efficiency, Mach number and wall temperature on the separation and aerothermal loads have been studied.

Real Gas Effects on a Planetary Re-entry Capsule

*† This paper provides a detailed investigation of nonequilibrium real-gas effects of hypersonic speed in the forebody region of a typical re-entry vehicle. A finite rate chemistry model based on the Scott model is implemented here and for an extensive investigation of the catalysis modeling relevance simulations with non-catalytic wall conditions are computed as well as those with full catalytic boundary conditions. Turbulence modeling is considered to investigate its coupling with finite rate chemistry. The method developed is then used to compute the detailed flow features of a hypersonic flow around the forebody of a re-entry vehicle. The computed pressure and shear stress coefficients along the profile are then analyzed and the stagnation heat flux is compared to the experimental data. A comparison with the results obtained by Kurotaki with his finite rate chemistry model is here presented as well.