Modal analysis of jet flow from a coaxial nozzle with central plug

The present paper deals with azimuthal analysis of a double stream flow with a central plug nozzle. Onera previous works on jet noise permited to validate a computation method that is in good agreement with measurments. The next step is to use file stored aerodynamic flow field from LES CFD simulations to understand the generation of jet noise through azimuthal decomposition. Firstly, configurations an d aerodynamic results are presented. Azimuthal decomposition method formulas are then given. Far field acoustics results are followed by rms pressure field on the stored region . After analyzing the rms pressure maximum for five lines parallel to jet axis, azimut hal composition is given for these lines. Line at r=0,405D passes through the maximum of rms pressure. All lines permit to conclude that mode m=0 is dominant in most regions of the jet flow field. The end of this analysis is focused on frequency influence on mode contribution and spatial repartition. This study gives clues to establish an identity card of the az imuthal structure of jet flow. This structure is believed to be very influent on jet noise genera tion and propagation to far field.