Interaction between the shear layer, shock-wave and vortex ring in a starting free jet injecting into a plenum

etc15 Tracking Number 129

While continuous free jets have been investigated and optimised during the last 60 years, the impulsively started jet is still relatively unexplored. We focus here upon the very first stage of a compressible free round jet, when the flow is only few diameters long and the vortex ring generated by the sudden expansion interacts with the shock-waves and the shear layer. Direct numerical simulations with more than 2*10^9 grid points are carried out, discretising the compressible Navier-Stokes equations to compute both the fluid flow and the noise radiated by the interaction of the shear layer, the shock-waves and the vortex ring in a compressible free round jet. As a result of the mentioned interaction, a sound level of 111[dB] at a distance of 100 diameters from the jet has been computed. An interaction between the shear layer, the shock-waves and the vortex ring has been investigated using numerical methods in an impulsively started supersonic free round jet and noise levels of order of the loudest acoustic phenomenon in the continuous jet have been identified and quantified.