Jet stability and noise computations using direct numerical simulation

The computations of axisymmetric jet noise with symmetric disturbances are investigated using the direct numerical simulation of the unsteady compressible Navier-Stokes equations. High order accurate numerical schemes are employed for the solution of the governing equations. The investigation shows that MacCormack schemes with operator splitting and minimum dispersion error can be used to predict noise radiated from subsonic and supersonic jets with low and high Reynolds numbers. In addition, different kinds of nonreflecting boundary conditions are used at the inflow and outflow boundaries. These boundary conditions include characteristic boundary conditions, buffer domain technique and perfectly matching layer method. The results indicate that the perfectly matching layer method is causing minimum wave reflections at the boundaries and this method is computationally less expensive than the other boundary conditions.; The computations are carried out for two and three-dimensional axisymmetric jets. Five cases for two-dimensional jets at different Mach numbers and Reynolds numbers are presented. The characteristics of the sound source in the near field are computed and the results show a good agreement with the observations. Moreover, a method is developed to compute the noise in the far field using the linearized Euler equations. The results computed in the far field agree with those obtained using Navier-Stokes equations.