1208 THE EFFECT OF UPSTREAM DISTURBANCE ON THE ANGLE OF SOUND EMISSION IN A SUPERSONIC ROUND JET

Abstract

The three-dimensional time-dependent compressible Navier-Stokes equations are numerically solved to study acoustic emission mechanisms in a supersonic round jet at high convective Mach numbers. A 5th-order compact upwind algorithm developed by Deng and Maekawa (1996)[1] is used for spatial derivatives and a 4th-order Runge-Kutta scheme for time advancement. The Navier-Stokes characteristic boundary conditions are used in the streamwise and radial directions and periodic boundary conditions in the azimuthal direction. Numerical results for the convective Mach number Mc = 0.97 are presented (Mc is defined by eq.(13) in Section2). Two different cases were investigated. The first case is the jet forced by the linear unstable modes. The second case is the jet flow forced randomly. The numerical results provide new physical insights into Mach wave generation nature in a supersonic round jet. Upstream disturbance conditions play an important role for the emission of the Mach waves in a supersonic jet. The numerical results show that the jet forced with a pair of first helical modes can indicate the elimination of Mach waves at restricted emission angles due to the interference of these modes. The pressure fluctuations generated by the growth of the opposite helical mode are lineally superposed into the jet near sound filed. Therefore, this result suggests that the direction of Mach wave radiation can be controlled by introducing of optimal helical modes in turbulent jets.