Influence of Nozzle Geometry on Jet mixing and Jet Installation Noise

Abstract

Jet installation with chevron nozzles beneath a wing significantly modifies jet noise at low frequencies, and its physical mechanism must be comprehended to develop efficient noise reduction solutions. A numerical investigation on the jet-installation noise with an SMC006 chevron nozzle is performed using Wall Modelled Large Eddy Simulation (WMLES) using the high-resolution CABARET method, accelerated on Graphics Processing Units. To simulate the jet installation, an SMC006 chevron nozzle with a penetration length of 20 degrees and length L is put at 2Dj vertically above the flat plate, resulting in a rise in noise levels at low frequency. The low frequency amplification is associated with the scattering of the near-field hydrodynamic pressure waves at the trailing edge. The numerical simulation for the baseline chevron is validated with the experiments performed at the University of Bristol. The properties of jet-hydrodynamic pressure variations and their effect on nozzle type at Mach = 0.5 is investigated. In order to understand the significance of chevron’s geometry on jet installation noise, the RBF algorithm is employed to modify the penetration length and angle of the baseline chevron nozzle from 5 degrees to 35 degrees, and chevron length from 0.5L to 1.5L. It is found that the chevron’s penetration angle has a strong influence on the hydrodynamic pressure field in comparison with penetration length. In addition, a hybrid semi-analytical hydrodynamic-edge scattering prediction model is implemented following the model of Lyu and Dowling [1] to analyse jet-installation noise for a modified chevron, using inputs obtained from isolated LES simulations. The implemented model captures correct physics for the baseline nozzle and shows noise reduction of 1-2dB at peak Strouhal number for low penetration angle chevrons.