Attenuation of sweep events in a turbulent boundary layer using micro-cavities

Abstract

In the present study, the turbulent energy production within a fully developed turbulent boundary layer has been reduced using a variety of flushed-surface cavity arrays with different geometries embedded within a flat plate. The cavity arrays manipulate the sweep events in the boundary layer by capturing and damping their duration and intensity. The size of the holes in the cavity array was selected to be comparable with the dimensions of the expected coherent structures, based on the friction velocity and the known spacing and sizing of the sweep events. The velocity fluctuations within the turbulent boundary layer were measured using hot-wire anemometry in a wind tunnel for a range of Reynolds numbers. The results show that when the orifice diameter is equal to a value of 60 times the viscous length scale there is a maximum reduction in the turbulence and sweep intensities of 13 and 14%, respectively. The results also demonstrated that for a cavity orifice diameter less than 20 times the viscous length scale, the sweep events are restricted and no events are captured by the array. Furthermore, if the diameter of the orifice exceeds 145 times the viscous length scale, separation of the shear layer occurs, causing an increase in the turbulence energy production in the near-wall region.