Induced Stall Cells on a NACA0015 Airfoil using Passive and Active Trips

摘要

An experimental investigation of stall cell formation on a NACA0015 with aspect ratio AR= 2.67 was conducted via oil flow visualization (OFV) and surface pressure measurements.A range of angles of attack near stall condition and at moderate to high Reynolds numbers(Re_c ≈ 105~ to 10~6) was explored. The work focused on exploring passively inducement of astall cell by adding full span or partial span trips, which were composed of balsa wood orzig-zag tape. The results showed that under some conditions, adding a localized trip willresult in the formation of stall cell(s). It is necessary that the trip induces threedimensionaldisturbance to the flow; otherwise, no stall cell will be formed. The motivationis to characterize flow behavior using passive trips and then ultimately to replace thepassive trips with an actuator of the same physical size in order to induce a stall cell. Theaforementioned actuator was mounted on the airfoil and pressure data were obtained. Itwas found that, when in the flush position, the actuator increased 3-D separation in theflow field. However, when fully extended to 2 mm, α= 14° and Re_c = 6.69∙10~5, theactuator caused the flow field to attach. The physical mechanism behind this behavior isunder investigation.