SUPERSONIC PLANE JET AT HIGHT CONVECTIVE MACH NUMBER(Plane Jet)

Abstract

The three-dimensional time dependent compressible Navier-Stokes equations are numerically solved to study acoustic emission mechanism in a supersonic plane jet at high convective Mach numbers using high-order compact upwind schemes. High-order compact schemes of 5th order developed by Deng and Maekawa (1996, 1997) [1] [2] are used for spatial derivatives and a 4th order Runge-Kutta scheme is employed for time advancement. Navier-Stokes characteristic boundary conditions are used in the streamwise and vertical directions and periodic boundary conditions in the spanwise direction. Numerical results for the convective Mach number Mc=1.17 are presented (Mc is denned by eq. (16) in Section 2). Two cases were investigated. The first case is the jet flow forced randomly. The second case is the jet forced by random disturbamces and linear unstable oblique modes. The numerical results provide new physical insights into three-dimensional structures and acoustic wave generation mechanisms in a plane turbulent jet. Upstream disturbance conditions play an important role for the evolution of the downstream structure, such as development of shear layers in a jet. Growth of the oblique mode is responsible for the A structure in a plane jet, which yields sooner decay of the centerline velocity. The result indicates that the jet forced with the oblique modes can mix faster with the surounding fluid medium than the jet forced randomly. The intense sound radiation observed in the randomly forced jet can be reduced by forcing with a pair of oblique modes.