THE EFFECT OF THE BACKING CAVITY ON THE CONTROL OF THE TURBULENT BOUNDARY LAYER BY THE APPLICATION OF A CAVITY ARRAY

Abstract

The results presented in this paper provide an insight into the effect of a cavity array on the turbulence production within a turbulent boundary layer. In the present study, the turbulent energy production within a fully developed turbulent boundary layer has been reduced using a flushed-surface cavity array underneath a flat plate coupled with an acoustic actuator. The size of the holes in the cavity array were selected to be comparable with the dimensions of the expected coherent structures, based on the friction velocity. Experimental measurements were taken in a wind tunnel at a number of locations along the array in the streamwise direction and at a variety of acoustic frequencies generated by the acoustic actuator. A maximum turbulence intensity and sweep intensity reduction of 11% and 10% respectively occurred at Reθ = 3.771 × 10 in the logarithmic region of the boundary layer when no drive frequency was provided. From this investigation it has been shown that the drive frequency of the acoustic actuator has no effect on the turbulence reduction by the cavity array. Instead the physical parameters of the array, including the number and diameter of the cavities in the array have a much more