Direct Numerical Simulation of Mixing Layer : Effect of Spanwise Disturbance

Abstract

The objective of this paper is to clarify the effect of the spanwise wavelength of an initial disturbance on the secondary instability of mixing layers. To achieve this purpose, we have performed a direct numerical simulation of a three-dimensional mixing layer using a spectral method. The results are reported for the case of an initial hyperbolic tangent velocity profile with periodic excitation. From these results, we have obtained the following conclusions : 1) streamwise and transverse velocity fluctuations are slightly affected by the initial spanwise wavelength ; 2) spanwise velocity fluctuation and streamwise vorticity reflect the effect of the initial spanwise wavelength ; and 3) the spanwise perturbation that has the wavelength equal to one-third of the streamwise wavelength has the maximum growth rate.