The problem of laminar-turbulent transition in boundary-layer flows is more than hundred years old. Physical mechanisms associated with excitation, propagation and nonlinear breakdown of different unstable disturbances have been studied by dozens of research groups and discussed in thousands of papers. However, a reliable transition prediction scheme is still beyond the horizon, especially for boundary layers at supersonic and hypersonic speeds. In this lecture we discuss the current state of the transition prediction problem for high-speed flows, highlight key issues and stumbling blocks and suggest some ideas on how to proceed with further developments of the physics-based methodology. These ideas are illustrated by the results obtained by our transition study group. In particular, it is demonstrated that the amplitude method, which is a rational physics-based method for transition predictions, can be implemented for certain high-speed configurations including: first-mode or second-mode dominated transition triggered by thermal fluctuations; first-mode dominated transition induced by solid particulates; cross-flow dominated transition induced by small local and/or distributed roughness on a supersonic swept wing. In connection with holistic computations of transitional boundary-layer flows, we discuss a new intermittency model based on the linear stability theory (LST). This model has been developed and incorporated into the Spalart-Allmaras RANS model. Predictions of the resulting hybrid LST+RANS method are compared with available experimental data.
Professor Alexander V. Fedorov is a leading researcher of Central Aerohydrodynamic Institute (TsAGI) and Associate Professor of Moscow Institute of Physics and Technology. He received his Ph.D. degree of Fluid, Gas and Plasma Dynamics form Moscow Institute of Physics and Technology in 1982. His current research interests focus on theoretical and computational modeling of stability and laminar-turbulent transition of compressible boundary-layer flows and laminar flow control. He has been in close collaboration with the Rockwell International Science Center (at present Teledyne Scientific and Imaging Company, Thousand Oaks CA) over 10 years. He also has been collaborated with the AFOSR/NASA National Center for Hypersonic Research in Laminar-Turbulent Transition, Graduate Aeronautical Laboratories of California Institute of Technology. He has published more than 150 papers and now his citations are 2479 according to google scholar. As a well-recognized scholar in the fluid dynamics, he has been awarded as Associate Fellow of the American Institute of Aeronautics and Astronautics. He received Zhukovsky Prize on Fundamental Research, TsAGI in 2006 and 2017.