A direct numerical simulation (DNS) was performed for the laminar-turbulent transition at Mach S over a flat plate. For triggering the transition to turbulence, temperature disturbances were introduced into the boundary layer by imposing an energy source term in the energy conservation equation. Low-frequency disturbances from 10 to 80 kHz which correspond to the first-mode waves were generated to investigate the interactions between low-frequency waves and the second mode. The growth of the wall pressure fluctuations showed that the second mode around 300 kHz was amplified with a low-frequency amplitude envelope by introducing low-frequency waves.
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