Antonio Schettino

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.

Shock Wave Boundary Layer Interaction in EXPERT Flight Conditions and "Scirocco" PWT

One of the most challenging problems of modern aerospace engineering is the prediction of hypersonic flows, both for the complexity of the required physical modelling and for the impossibility to duplicate in wind tunnel the real flight conditions due to the high energy levels required. Experimental and numerical investigation techniques must be combined and mutually validated and improved. In the frame of the ESA-EXPERT programme, the main goal of Payload #07 is to design and execute a flight experiment on shock-wave boundarylayer interaction with flow reattachment on control surfaces in order to collect flight data to be used for a post-flight analysis and assessment of a methodology for the extrapolation-toflight of the interesting parameters of such flows. Another aspect of this payload concerns with the duplication of the conditions over the flap in a high enthalpy ground facility; to this aim, it is necessary to correlate the numerical and experimental plasma wind tunnel results with those predicted and, then, measured during the flight, the goal being to understand the test conditions necessary to reproduce the mechanical (pressure) and thermal (heat flux, temperature) loads acting on the control surface device (extrapolation-from-flight and toflight procedure).

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 ...

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.

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.

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.

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...

Laminar-turbulent transition flight experiment on the EXPERT capsule

Laminar-turbulent transition is commonly recognized as an important factor in the design of re-entry vehicles. In the framework of the European project EXPERT, organized by the European Space Agency (ESA), CIRA and ONERA have worked together to design and implement on the EXPERT capsule an experiment on natural transition. The aim of the present work is to summarize the status of the Payload 04 showing all the activities performed up to the shipment phase.