Abstract
A hybrid method was explored to investigate the generation and near-field radiation of aerodynamic sound from an unsteady turbulent flow over a two-dimensional open cavity and three-dimensional jet flow. A two-dimensional cavity model was established to study the unsteady flow and radiated jet sound. It was revealed that the radiated sound that generated by the boundary layer separation and vortex impact cavity wall intervened in the front of the cavity, and an obvious interference phenomenon appeared. The far-field radiated sound generated by the cavity presented obvious directivity, and the sound pressure in the area located at 45°–135° interval was much higher. Then, the unsteady turbulence jet noises of the elliptical and rectangular nozzles were analyzed. It was revealed that the scale and intensity of the vortexes generated by the elliptical nozzle were larger than those by the rectangular nozzle. The jet noise of the elliptical nozzle is lower than that of the rectangular nozzle. Besides, the sound pressure distributions of the two nozzles presented obvious directivity. The sound pressure in the short-axis direction of the nozzle section was higher than that in the long-axis direction.
Highlights
The vortex structure is the main aerodynamic sound source in the flow field.[1]
The radiated acoustic produced by the boundary layer separation and vortex impact cavity wall intervened, and an obvious interference phenomenon appeared
The sound pressure in the area located at 45°–135° interval was much higher, and the directivity of the acoustic field had no change with the increase in the observation distance within a certain spread range
Summary
The vortex structure is the main aerodynamic sound source in the flow field.[1]. The accuracy of the sound source prediction has great influence on the calculation of the aerodynamic sound. The ‘‘hybrid method’’ is often used to study the radiated turbulence jet noise.[5,6,7,8] Its core idea is to calculate the unsteady viscous compressible or incompressible flow first and to calculate the radiated sound field by the inviscid linear Euler equation (LEE) or the wave equation It greatly reduces the cost of the aerodynamic noise simulation and makes the far-field acoustic calculation possible. An additional source term is introduced into the control equation of this region to force the transient calculation results to be infinitely close to the corresponding reference value of the quasi steady flow field.
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