Experimental investigation of pressure measurement and airfoil characteristics at low Reynolds numbers

A low-speed wind-tunnel investigation is presented that elucidates the effects of pressure tapping layout on observed pressure distributions. The characteristics of a 16% thick S8036 profile used in the study are explored. The set Reynolds number Re range was 75,000,100,000,150,000 and 200,000. Effects of streamwise, inclined, and wing-root taps were studied. Results encompassing pressure plots, lift coefficients, and surface flow visualization are presented. All data are compared to numerical predictions using Xfoil. The data show good agreement between experiment and Xfoil for most cases; most disagreement is in the location and extent of the laminar separation bubble. The results show that the streamwise taps may cause premature transition depending on the test Reynolds number and wing incidence. For a given angle of attack, agreement between the streamwise and inclined pressure ports improved with the Reynolds number, while for Re <= 100, 000, the accord improved with wing incidence. Tappings at the wing root generally indicated reduced pressure compared to those along the span, although agreement between all three tap locations was reasonable downstream of the bubble reattachment. As cited in the literature, the effect of increasing Reynolds number was to shorten the laminar bubble, not by altering the location of laminar separation but by earlier transition and reattachment. Incidence was noted to move the bubble toward the leading edge and to reduce its length slightly. Both the laminar and turbulent sections of the bubble were seen to demonstrate Reynolds number dependency. Reynolds number effects were also present in the magnitude of the loading upstream of bubble reattachment, but were not evident from the location of reattachment aft.