DNS Study of Wall Temperature Effects on the H-type Transition in a Transonic Boundary Layer

Wall temperature influences the stability of a boundary layer. For a compressible boundary layer, the velocity and temperature fluctuations couple nonlinearly, and the coupling affects the dynamics in transitional and turbulent regimes. To investigate such nonlinear physics in detail, a direct numerical simulation (DNS) is desirable. In this study, the wall temperature effects on the laminar-to-turbulent boundary layer transition in a transonic boundary layer (Ma=0.8) over an isothermal flat plate are investigated with the DNSs. Three distinct isothermal wall conditions are considered: quasi-adiabatic, 10% heated, and 10% cooled. In the present DNSs, we provide tiny wall-normal velocity disturbances mimicking blowing and suction on the wall to induce the so-called H-type transition. As a result, the wall heating promotes the H-type transition onset while the wall cooling delays it considerably further downstream, compared to the quasi-adiabatic case. In the transitional regime, in particular, we observe that the wall cooling elongates the staggered lambda vortices and delays their breakdown to turbulence.