Flow field analysis for double stream nozzle: application to jet noise

Abstract

The present paper deals with jet flow and noise comparisons between experimental data and numerical simulation results. ONERA took part of EU CoJeN (Coaxial Jet Noise) project which permitted to acquire a large experimental database at the end of the project. Firstly, a summary of experimental and numerical results is presented together with a complete list of available data. Experimental set-up and methods are briefly recalled; then, a synthesis of data is made in view of comparisons. Finally, comparisons between experimental and numerical results are presented. The comparisons are based on mean values, two-point velocity correlations and near field pressure levels and spectra. The objectives of these comparisons are to qualify the simulation and to understand physical phenomena in coaxial jet. This work permitted to document the discrepancies observed in the LES simulations. In particular it is shown that a higher level of turbulence a few diameters downstream of the nozzle exit maybe responsible for an over-estimation of far-field noise levels. This overpredicted energy transfer to turbulent flow is also responsible of a too short potential core. Although the overall content of the simulation seems satisfactory, except the exaggerated turbulence growth, it is proposed to improve the numerical simulations by somewhat reducing the grid coarsening in the first diameters downstream of the nozzle exit. This should permit to improve noise prediction of jet flows.