Design, execution and numerical rebuilding of shock wave boundary layer interaction experiment in a plasma wind tunnel

The present chapter reports the design, execution and numerical rebuilding of a plasma wind tunnel experimental campaign with the aim to analyse shock wave boundary layer interaction phenomena in high enthalpy conditions.This particular flow pattern could arise in proximity of a deflected control surface,thus generally causing a separation of the boundary layer and a loss of efficiency of the control surface itself; moreover, high mechanical and thermal loads are generally induced at the flow reattachment over the flap. Therefore, the analysis of this problem is crucial for the design and development of the class of hypersonic re-entry vehicles, considering that, even though it has been widely analyzed in the past, both from an experimental and theoretical point of view, by describing its physical features, only few studies have been carried to analyse the phenomenon in high enthalpy real gas and reacting flow conditions.The activity has been developed by analysing the flow phenomenon of interest in different conditions: i) hypersonic re-entry conditions considering the ESA EXPERT capsule as a workbench, and ii) ground-based facility conditions considering the CIRA Plasma Wind Tunnel "Scirocco". The aim has been the correlation of the results predicted, by means of a CFD code, and then measured through specific experiments suitably designed, in these two different environments.To this effect, a flight experiment has been designed to be flown on the EXPERT capsule along the re-entry trajectory in order to collect flight data (pressure, temperature and heat flux) on the shock wave boundary layer interaction phenomenon to be used for CFD validation and, additionally, as a reference point for the extrapolation-from-flight methodology developed accordingly. Requirements for the experimental campaign to be performed in the "Scirocco" facility have been derived considering the most critical and interesting points along the EXPERT trajectory. A suitable model, representative of the EXPERT geometry in the zone of interest, i.e. the flap region, has been conceived by defining the main design parameters (nose radius, length, width, flap deflection angle)and an experimental campaign has been delineated, the aim being to reproduce on this model the same mechanical and thermal loads experienced ahead and over the EXPERT full- scale flap during the re-entry trajectory. Suitable facility operating conditions have been determined through the developed extrapolation-from-flight methodology; the design and the analysis of shock wave boundary layer interaction phenomenon has been done by focusing the attention mainly to the catalytic effects over the interaction induced by the different behaviour in terms of recombination coefficient of the materials involved in the problem under investigation.Once defined the design loads, the model has been realized and tested in the Plasma Wind Tunnel Scirocco under the selected conditions. The numerical rebuilding, showing a reasonable good level of reproduction, has been also carried out, even though the validation of the entire extrapolation-from-flight and to-flight developed methodology could be completed only after the EXPERT flight currently planned in mid 2011.