Towards natural transition in compressible boundary layers

Abstract

Abstract : This final report concerns the results obtained in the project titled: Towards natural transition in compressibleboundary layers, with Grant number FA9550-11-1-0354-2, in the period 30-09-2011 to 29-03-2016, with Dr. James M. Fillerup serving as program manager. In this project, a DNS code was developed to investigate problems on transition in compressible boundary layer on a flat plate. Code validation test were performed for linear and nonlinear stages of transition, in incompressible and compressible regimes. The focus of the present work is to investigate natural transition in compressible subsonic boundary layer modeled by wave packets; and perform a preliminary study of transition generated by white noise. Three main problems were considered, namely, numerical simulation of the experiment [54] on incompressible boundary layer, the influence of compressibility on wave packet evolution at subsonic Mach numbers and finally, a preliminary study of the evolution of a white noise perturbation in the boundary layer at Mach 0.2 and 0.9. Comparison between numerical and experimental results [54] are in remarkably good agreement in the linear and nonlinear stages, in both, spatial and Fourier spaces. Simulation of this experiment and the analysis carried out for wave packets in the incompressible boundary layer is not available in the literature. The nonlinear modal analysis performed established definitely the existence of tuned fundamental and subharmonic resonance of H-type and K-type in the packet.