Effects of geometric disturbances on the wake of an axisymmetric bluff body

Abstract

This study assesses the effectiveness of straight-edged and sinusoidal geometric disturbances (skirts) in reducing the base drag of a three dimensional axisymmetric bluff body. The current investigation stems from the previous successful application of this passive technique to a two dimensional bluff body. Wind tunnel tests were conducted on a projectile-like model with a streamlined leading edge and a circular base. The effect of the extension coefficient and of the disturbance wavelength on the base pressure distribution and the shedding frequency were investigated. The results show that the extension coefficient is the dominant parameter influencing the base pressure increase. Proper selection of the extension coefficient can produce an increase in the base pressure of up to 25% (straight-edged disturbance with extension coefficient of 0.16). The effect of the disturbance wavelength however, is less evident. The weak azimuthal dependence of the base pressure distribution as observed from the pressure contours suggests that the influence of the wavelength may be comparatively weaker. There is also evidence that a straight disturbance may outperform a wavy disturbance. Finally, the dominant wake frequency of the baseline is generally retained with the application of the sinusoidal disturbances but displays a marked drop for the straight disturbances. Copyright © 2008 by The Authors.