Application of surrogate models to stability analysis and transition prediction in hypersonic flows

Abstract To increase the efficiency and convenience of stability-based transition prediction in flow simulations, simplified methods are introduced to substitute direct stability analyses for rapid disturbance growth prediction. For low-speed boundary layers, these methods are mainly established based on a self-similar assumption, which is not applicable to non-similar hypersonic flows over blunt cones. The objective of this article is to investigate the application of surrogate models to substitute linear stability analysis for non-similar flows on blunt cones, focused on input parameters for boundary-layer (BL) profile description. Firstly, correlations analyses between BL edge and profile parameters are conducted, along with a self-similar analysis and a discrete BL profile analysis, which present four groups of BL characteristic parameters. Secondly, using these parameters as inputs, surrogate models are built for disturbance growth prediction over an MF-1 blunt cone at flight experiments. Results show that, using 4 BL edge parameters and a BL shape factor {Ue, Te, ρe, ηe, H12} can achieve comparable accuracy with using 16 discrete BL profile parameters, which is also more precise than using merely self-similar parameters or BL edge parameters. Thirdly, the established surrogate models are validated in stability analysis and transition prediction over the MF-1 blunt cone at the moments of t =17s~22s in flight experiments. Compared with direct linear stability analyses, the mean relative error of predicted disturbance growth rates by surrogate models is 8.0% and the maximum relative error of N factor envelopes is 6.6%, which indicates the feasibility of using surrogate models to substitute stability analysis in transition prediction of non-similar flows over hypersonic boundary layers.