Direct-Numerical Simulation with the Stability Theory for Turbulent Transition in Hypersonic Boundary Layer

Laminar-to-turbulent transition in hypersonic boundary layer is numerically investigated using the direct-numerical simulation (DNS) method combined with the linear stability theory (LST). The DNS-LST framework is validated first for 2D hypersonic boundary layer. The growth of the Mack second mode is matched well to previous DNS data. A complete 3D turbulent transition at Mach 6 is computed in the current DNS to demonstrate the capability of the current method for a whole 3D turbulent transition scenario. Two modes are assigned at the DNS inlet for the fundamental breakdown in the hypersonic boundary layer: the Mack second mode (the fundamental mode) and the pair of oblique waves of the fundamental frequency. These instability modes are obtained from the stability analysis. The current DNS successfully resolves the 3D turbulent transition in the hypersonic boundary layer. Computational data are investigated to identify major flow features associated with the fundamental breakdown phenomena. Major instability modes are analyzed in the late transient stage.