On the optical properties of a supersonic mixing layer

Abstract

This chapter investigates physical properties of spatially developing shear layers between two flows of different velocities. The two fluid streams are supersonic and the convective Mach number is greater than unity in most cases. The two-dimensional compressible Euler equations are solved directly using the explicit Godunov method. A hyperbolic-tangent velocity profile is adopted for the initial streamwise velocity distributions at the splitter plate. The chapter calculates temporal and optical statistics of the mixing layer. The optical properties of the mixing layer are determined by computing the Strehl ratio. Although the growth rate of a supersonic mixing layer is much smaller than that of a subsonic mixing layer, it is found that the far-field peak intensity is less than that due to a subsonic mixing layer at the same velocity ratio and density ratio. The chapter also provides the comparison between the values of Strehl ratio due to supersonic shear layer and a subsonic shear layer with the same velocity ratio and density ratio. Although the growth rate of supersonic shear layer is unusually small, the Strehl ratio is not as high as expected because the shock/shear layer interaction region enhances the optical random phase errors in the beam passing through the shear layer that can substantially reduce the maximum intensity to which the beam can be focused in the far-field.