Sébastien Paris

In-Flight Hypersonic Roughness Induced Transition Experiment

The development of an hypersonic isolated roughness induced transition experiment has been carried out based on experiments and numerical computations. This experiment has been developed in the frame of the European EXPERT program, which has been developed to carry multiple flight experiments aimed at improving the understanding of critical aerothermodynamic phenomena. The design of this experiment consist in the in the cho ice of the isolated roughness element and the inflight instrumentation. The choice of the roughness shape and dimensions has been made experimentally in a Mach-6 facility and are based r espectively on aerodynamic considerations and on wind-tunnel validated transition criteria. Some numerical thermal computations have been performed for the verification of the roughness des ign and of the ability of the instrumentation to detect transition. Finally, a fundamental investiga tion of the flow-field around and downstream of isolated roughness has been done for preparing the post-flight analysis.

Experimental Characterization of Hypersonic Nozzle Boundary Layers and Free-Stream Noise Levels

Pitot pressure surveys of the Longshot hypersonic contoured nozzle in the von Karman Institute are presented. Measurements use a rake of pitot probes at four locations along the nozzle axis from half the nozzle length down to the exit. Laminar and turbulent numerical simulations are used for comparison. A good agreement is obtained with the turbulent computations conrming the existence of turbulent boundary layers along the nozzle walls. The uniformity of the free-stream parallel ow is characterized by a standard deviation of 3.5%. The free-stream noise levels determined from pitot pressure uctuations are about 7.5% and slightly lower inside the nozzle. These are comparable with the levels recorded in other similar hypersonic wind tunnels. Some ow divergences are shown to be possibly correlated to a discontinuity in the contour of the nozzle. The test time available at various locations is also determined and is shown to depend upon the location considered along and across the nozzle.

Design of static pressure probes for improved free-stream characterization in hypersonic wind tunnels

Slender fast-response static pressure probes are tested in the Longshot hypersonic windtunnel with free-stream Mach number larger than 10 and Reynolds number 30000 . ReD . 60000 based on the probe diameter. They aim at improving the characterization of the freestream. Numerical simulations predict the wall pressure measured to be within 5% of the free-stream static pressure. The viscous effects along the probes are found experimentally to be limited for L/D > 16.5 in agreement with numerical results. Limited influence of the angle of attack of the probes is found for α < 2 ◦ thanks to the probing geometry used. The free-stream quantities at the nozzle exit (Mach, Reynolds...) are derived from the static pressure measurements and compared to those estimated assuming an isentropic nozzle flow expansion. The usefulness of static pressure probes is demonstrated through their ability to detect possible non-isentropic nozzle flow expansions which do not influence traditional measurements such as the test section stagnation pressure. This direct access to free-stream quantities allows to significantly improve the accuracy on the free-stream quantities and benefits to the characterization of hypersonic wind-tunnel flowfields.

Design of a laminar-turbulent transition flight experiment

*† ‡ § ** 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, ONERA and VKI are working together to design and implement on the EXPERT capsule an experiment on induced transition. The aim of the present work is to summarize and test the main correlations commonly used to estimate transition in hypersonic regime, applying them to the flight of the EXPERT capsule. An experimental test campaign has been also carried on in order to verify the reliability of such correlations in wind tunnel conditions representative of the EXPERT flight. Finally, the preliminary sensors layout proposed for the EXPERT capsule is shown for the flight is foreseen in 2007.

Investigation of the boundary layer characteristics on a re-entry vehicle

The goal of this project is to develop a payload for the European EXPERT program. The task of this package is to characterize the boundary layer around the KHEOPS reentry vehicle at different conditions during the trajectory. This will be performed using Pitot probes (dynamic pressure measurements) and electrostatic probes (electron density measurements). Numerical simulations are used to determine the conceptual geometry of the probe rake, then this geometry is optimized experimentally for resisting the high thermal and mechanical loads and for providing high quality data. Finally, the complete system (rake + acquisition system) will be tested before flight.