To investigate the influence of initial disturbance of different wavelengths on flow and noise of two-dimensional time-developing mixing layer
a direct numerical simulation method is suggested. By multiple-scale expansion technique
the conservative continuity
momentum and energy equations are accurately recovered from Boltzmann equation of coupled double distribution functions. The characteristic boundary condition is combined with Boltzmann equation to satisfy the non-reflecting condition. High-order temporal and spatial discretization approaches are employed to solve Boltzmann equation to analyze five different mixing layers. The results show that high frequency disturbances mainly control the pairing and winding of vortices
while low frequency disturbances mainly control the rotating and migration of vortices. The evolution of vortex pairing is similar to a rotating quadrupole source. The disturbance energy radiates as plane waves to the far field at sonic speed.
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references
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