The overall objective of this proposal is the identification of essential effects and mechanisms that lead under perturbed freestream conditions and various types of roughness distributions to laminar-turbulent transition on the frontbody of blunt reentry vehicles. To satisfy this objective the determination of the pertubations in the wind tunnel flow of the Hypersonic Ludwieg Tube Braunschweig (HLB), which is based on experimental data from TP2-BS and direct numerical simulation results from TP1 , will be improved by using a stagnation-point probe. This is a consequent result of the first funding period in which it was shown that the cone probe has unfavorable properties for the modal decomposition of the measured tunnel noise. The pertubation data of the wind tunnel in conjunction with novel transition experiments in the HLB will be linked to the determined tunnel noise and used to improve correlations of transition and tunnel noise. In the numerical investigations in the second funding period, the interaction of the determined tunnel noise and distributed roughness on the forebody of a blunt reentry vehicle will be analyzed. Since it was shown in TP2-GÖ that modal growth can not be expected for the reentry vehicle in the current Reynolds number range of the HLB, non-modal transient growth is investigated in the wake of the roughness. Therefore, it is to be analyzed how tunnel noise under certain conditions excites stable boundary layer modes and such influences transient growth. Next, the influence of various arrangements of deterministic distributed roughness is investigated to understand whether or not the roughness arrangement has a fundamental impact. If this is not the case, easily parameterizable deterministic distributed roughness can be used in future numerical and experimental investigations to mimic more realistic stochastically distributed rough surfaces.
DFG Programme
Research Grants
