Velocity Fluctuations within the Turbulent Flow over a Flow-excited Helmholtz Resonator

Abstract

An unstable turbulent shear layer over a Helmholtz resonator can produce strong pressure fluctuations within the resonator at the resonance frequency. These pressure fluctuations are responsible for generating flow oscillations over the orifice. Understanding of this process requires an appropriate model to predict the characteristics of the grazing flow over a three dimensional resonator. In this paper using a Large Eddy Simulation (LES) of the three dimensional shear flow over a flow-excited resonator, the amplitude and frequency of the velocity fluctuations have been predicted. The simulation results were compared with an experimental study and proved the high accuracy of the model to calculate flow characteristics over the resonator. All simulations were carried out at a subsonic regime for various flow inlet conditions. The results were used to predict the effects of the free stream velocity and the thickness of the turbulent boundary layer on velocity fluctuations within the shear layer.