Numerical modelling of jets exiting from the ASME and conical nozzles

Abstract

Two isothermal round jets at a Mach number of 0.9 and a diameter-based Reynolds number of 2 × 10 5 have been computed by compressible large-eddy simulation using highorder finite differences on a grid of 3.1 billion points. At the exit of a pipe nozzle in which a trip forcing is applied, they are characterized by flow parameters, including the momentum thickness and the shape factor of the boundary layer, the momentum-thicknessbased Reynolds number, and the peak turbulence intensity, which roughly match those found in experiments using two nozzles referred to as the ASME and the conical nozzles. The nozzle-exit boundary layer is therefore in a highly disturbed laminar state in the first jet, and in a turbulent state in the second. The exit flow conditions, the shear-layer and jet flow fields, and the far-field noise provided by the highly-resolved simulations are described and compared. The jet with the ASME-like initial conditions develops a little more rapidly with slightly higher turbulence levels than the other. Overall, however, the results obtained for the two jets are very similar, and they are in good agreement with measurements available for Mach number 0.9 jets. This is in particular true for the farfield pressure spectra. As the ASME nozzle has been reported to yield higher noise levels than the conical nozzle, this suggests that the nozzle-exit conditions of the present jets do not adequately reflect those in the experiments and/or that the link between the noise differences and the jet initial conditions using the two nozzles is not as simple as was first thought.