Skin-friction reduction on body of revolution using boundary-layer alteration devices

The effect of boundary-layer alteration devices (BLADEs) on the characteristics of a turbulent boundary layer on an axisymmetric body of revolution in nominally zero pressure gradient incompressible flow is experimentally studied. The Reynolds numbers based on momentum thickness at the BLADEs' position were varied front 2610 to 6500. All BLADE configurations that were examined, including single-element ones, are shown to be capable of reducing skin friction in the downstream region. A tandem BLADE configuration is found to be more advantageous than the single-element configuration. The tandem configuration, formed by two flat ring elements with a chord length within 75% of the boundary-layer thickness, reduces the net drag by at least 15% compared to the regular flow. An enhanced drag reduction is also observed for small positive angles of attack of the BLADE. Finally it is found that an increase in the chord length of ring elements degrades the BLADE's effectiveness.