DNS of Hypersonic Boundary Layer Transition

Abstract

In the turbulent transition of hypersonic boundary layer, the secondary mode fluctuation at a frequency (several hundred kHz) higher than the primary mode (TS wave) plays a dominant role. In recent years, the secondary mode fluctuation grows by interfering with the low frequency fluctuation has been observed in hypersonic wind tunnel tests, but the conventional linear stability analysis cannot explain this, and it is necessary to establish a new theory considering the nonlinear effect. The author’s research group aims to capture the growth process of secondary modes that interfere with low-frequency modes by direct numerical simulation (DNS) and to obtain the data necessary to construct a nonlinear theory. In this paper, we attempted to generate turbulent transitions by adding a low-frequency temperature disturbance of 10 kHz to the boundary layer through an energy source term. As a result, we successfully captured the process of turbulent transitions in which high-frequency secondary modes different from the added frequency are excited by DNS.