The secondary Instability of a planar supersonic shear layer at Mc=0.5 has been simulated and studied with a direct numerical simulation (DNS) method. In the present numerical method, Navier-Stokes equations in the perturbation form are solved with a finite difference method of the third order accuracy, and the stability is analyzed on the evolution of disturbing waves simulated in the shear layer. The three-dimensional nonlinear spatial problem of a planar supersonic mixing layer is solved by introducing a two-dimensionaldisturbing waves on the lateral middle line of the inflow boundary. Along with the development of two-dimensional unstable perturbation vaves in the shear layer, the secondary instability takes place and develops in the downstream of the shear layer flow.With different frequencies of disturbance waves, the developments of secondary instability are different. For the disturbance circular frequency of 200.0, the secondary instability takes place and grows rapidly, but for the disturbance circular frequency of 100.0, the secondary instability does not grow. With this finding, the controlled three-dimensional structure evolutions have been studied.
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