On vortical flows shedding from a bluff body with a wavy trailing edge

Abstract

Studies have shown that shaping the trailing edge of a quasistreamlined bluff body in the form of a sinusoidal wave can result in substantial base pressure recovery. In this paper, direct numerical simulations at a Reynolds number based on base height of 2500 are used to understand the flow characteristics associated with the observed drag reduction. In particular, the effects of the wavelength of the sinusoidal disturbance on the drag coefficient, vortex shedding mechanism, and frequency selection are examined. Numerical flow visualizations compare favorably to previous experimental observations and the results confirm that there is a range of wavelengths where significant drag reduction is possible. A sinusoidal trailing edge with fixed amplitude and a wavelength which is five times the base height produces the largest reduction of more than 30% in the mean drag coefficient compared to a straight trailing edge. The drag reduction is associated with known observations such as a lengthening of the mean recirculation region, a marked drop in the velocity fluctuation at the dominant frequency of the wake and a relative increase in streamwise vorticity. Although the presence of vortex dislocations is linked with a reduction in drag, the occurrences of these structures do not yield the optimum configuration. Rather, the maximum reduction in drag appears to coincide with the transition of the vortex shedding process from a spanwise-irregular to a spanwise-regular mode characterized by spatially well-organized structures along the span. © 2008 American Institute of Physics.