Use of wall suction in half model wind tunnel testing
2010-06-25T10:47:44Z (GMT) by
The half model wind tunnel technique suffers from aerodynamic loses due to the interaction of the tunnel wall boundary layer with the flow over the model and the formation of a horseshoe vortex in the model-floor junction. The vortex is believed to contribute to the degradation of the half model aerodynamic performance. An attempt was made to reduce the aerodynamics losses by modifying the junction horseshoe vortex through the use of localized suction just upstream of the model leading edge. Wind tunnel tests on a rectangular and untwisted, wing only, modified LS(1)-0413 half model were conducted at Reynolds numbers of 0.44 x 10(6), 0.88 x 10(6) and 1 x 10(6). Without suction the force and moment balance measurements of the half model showed the anticipated deviation from full model values, e.g. lower lift curve slope and higher drag values. Effects of localized suction were limited to Reynolds number of 0.44 x 10(6) and improvements were seen only near stall angles of attack. Flow visualization for the no suction case showed that a horseshoe vortex did not exist over much of the incidence range for this particular model and hence there was little room for suction to effect junction flow. Near stall, suction removed the horseshoe vortex around the upper surface of the model and significantly reduced flow separations occurring in the model-floor junction, leading to the improved stall characteristics.