Time-dependent prediction of the unsteady pressure near-field from an under-expanded jet

The near field of an under-expanded air jet issuing from an axi-symmetric convergent nozzle is investigated by Implicit Large Eddy Simulation at a nozzle pressure ratio of 2.27. Estimates are obtained of the tonal components of the unsteady pressure at locations representative of the engine to fuselage distance in a civil transport aircraft. At this relatively short distance from the jet axis, the radiating acoustic pressure field combines with the ‘hydrodynamic’ pressure perturbations from the jet shear-layer structures, resulting in a combined aerodynamic and acoustic forcing pressure field. The predictions offer useful insight for predicting cabin noise at cruise in civil transport aircraft fitted with high-bypass ratio engines.