Raffaele Votta

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.

Analysis of Bridging Formulae in Transitional Regime

The most suitable method to compute aerodynamic forces of a spacecraft, at first stage of a design, relies on bridging formulae. There are two kinds of bridging formulae: global and local. The global formulae rely on knowledge of spacecraft aerodynamic force coefficients in continuum and in free molecular flow. The local formulae calculate the skin friction and pressure coefficients on the body surface; the global aerodynamic coefficients are then computed by integration. The aim of this work is to analyze the widely accepted local formulae by Potter and by Kotov. To this purpose, a simple body, like a sphere, has been preliminary considered and the results have been compared with those from the DSMC code DS2V. This comparison led to the corrections of the computation of the skin friction and pressure coefficients. These corrections have been applied to the Potter formula. On the other hand the original Kotov formula showed good results for the pressure coefficient at high altitudes. Therefore a merge of ...

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.

Influence of chemical models on heat flux for EXPERT and Orion capsules

The computation of heat flux on two current re-entry capsules, European eXPErimental Reentry Testbed (EXPERT) and Orion, has been carried out by a direct simulation Monte Carlo code (DS2V) and by a computational fluid dynamic code (H3NS) in transitional regime, considering both non-reactive and fully catalytic surface. These capsules have been chosen for this analysis because they have been characterized by completely different shapes and re-entry trajectories. DS2V and H3NS use the Gupta and the Park chemical models, respectively. The results showed that the heat flux predicted by DS2V is always higher than that predicted by H3NS. Therefore, a sensitivity analysis of the chemical models on the heat flux has been carried out for both capsules. More specifically, the Park model has been implemented in DS2V as well. The results showed that DS2V and H3NS compute a different chemical composition both in the flow field and on the surface, even when using the same chemical model (Park); therefore, the different results obtained from the two codes can be attributed mostly to the different methodology used in handling all chemical processes.

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.

Analysis of Aero‐Thermodynamic Behavior of EXPERT Capsule in Transitional Regime

The aerodynamic behavior of the EXPERT capsule has been already widely studied at low altitudes. In order to broaden the aerodynamic data base of the capsule, additional computations of the aerodynamic forces and an evaluation of the longitudinal stability and fluctuation of the pressure center have been carried out in the altitude interval 80–105 km. The effect of the rolling angle has been also evaluated. As EXPERT, in the considered altitude interval is in transitional regime, computations have been made by the DSMC code DS3V. Heat flux along the capsule surface has been also evaluated. This is an important topic because the nose and the frustum are made of low and high catalyticity materials, respectively. Computations, already performed in continuum regime by the CFD code H3NS, showed that, at the nose‐frustum junction, an abrupt and strong peak of heat flux is present. In this work, this problem has been analyzed also in transitional regime. For this application, the DSMC 2‐D code DS2V, requiring sm...

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.

Preliminary Design of a 30kN Paraffin-Based Hybrid Rocket Engine

One of the objectives of the HYPROB program is the development of tools, design and manufacturing methodologies applicable to hybrid systems and the verification of these technological developments through the realization and test of a 30 kN rocket engine. The technological demonstrator is based on nitrous oxide (N2O) as oxidizer and paraffin as propellant and will have most attractive capabilities of hybrid systems compared to solid or liquid engines, as throttability and re-ignition. The project targets to achieve a TRL of enabling technologies for hybrid propulsion equal to 5. The paper reports the study logic defined to achieve the goals of the project and the status of the technical activities related to the preliminary design of the demonstrator, based on a design tool developed ad-hoc.

Advanced Models for Prediction of High Altitude Aero‐Thermal Loads of a Space Re‐entry Vehicle

The analysis of the rarefaction effects in predicting the main aero‐thermal loads of a Space re‐entry vehicle is presented. It is well known that the Navier‐Stokes equations fail in rarefied regimes and other approaches must be used. In the present paper different configurations have been simulated by using the Direct Simulation Monte Carlo method. Moreover, slip flow boundary conditions have been implemented in a Navier‐Stokes code in order to extend the validity of the continuum approach to the transitional flow regime. Finally, bridging formulas for high altitude aerodynamics of winged bodies have been used. Firstly, two simple geometries have been analysed, specifically designed to study the phenomenon of shock wave boundary layer interaction: a hollow cylinder flare, for which some experiments are available; and a blunt‐nosed flat plate/flap model designed and tested at the Italian Aerospace Research Centre. The other configurations taken into account are, respectively, an experimental winged re‐entr...