HYPersonic bluff body flows – CHYP

This project is concerned with hypersonic bluff bodies, such as those observed on civilian and military reentry vehicles. One of the critical steps in the design of these objects is the knowledge of the average drag as well as of the unsteady loads generated by the fluctuations of the flow-field. These quantities are difficult to predict due to the complexity of the flow which combines shear layers, shocks, subsonic, supersonic and recirculating regions. Existing prediction methods look for steady solutions of the Navier-Stokes equations (with a turbulence model). These methods therefore overlook the strong large-scale fluctuations that exist in the near-wake of such vehicles, which explains their lack of precision and robustness.

This project aims at validating new prediction methods (ZDES unsteady computations and stability analyses in the frequency domain) that may accurately reproduce the fluctuating field. For this purpose, experimental databases at a Mach number of M = 4 will be produced over a wide range of Reynolds numbers (in laminar rarefied regime and in turbulent regime). Measurements of unsteady and mean static pressure at the base will in particular be compared with measurements of the density field in the near-wake. These experimental results will be compared with those obtained with the new prediction techniques mentioned above, in which some of the forcing terms will have been calibrated by comparison with the experiment. Finally, semi-empirical models for the prediction of mean drag will be extended to this high Mach number and stochastic reduced models reproducing the unsteady dynamics (and thus the loads) will be constructed.

The M = 4 tests in turbulent regime will be carried out at ONERA / Meudon and the tests in rarefied conditions by the CNRS-ICARE laboratory in Orleans. Two techniques of quantitative measurement of density field will be compared: a technique based on wavefront imagers by the PHASICS company and a technique of holographic interferometry by ONERA / Lille. Steady computations will be carried out by CEA / CESTA, unsteady computations, stability analyses, semi-empirical modeling and stochastic models by ONERA / Meudon.