Vortex Roll-Up from an Elliptic Wing at Moderately Low Reynolds Numbers

An experimental investigation of tip-vortex roll-up was undertaken at moderately low Reynolds numbers for an elliptic wing with a NACA 66_2 - 415 section. Flow visualization and laser Doppler velocimetry measurements were carried out to examine the flow in the vortex core and the tangential velocity distributions around the core. Separation was observed on both sides of the foil for Reynolds numbers up to 5X10^5. The observed changes in the location of separation and reattachment with angle of attack and Reynolds number were adequately predicted by laminar boundary-layer calculations. Axial and tangential velocity profile measurements were made at Reynolds numbers up to about 5X10^4. The vortex core radius was found to grow with increasing angle of attack, increasing downstream distance, and decreasing Reynolds number. A comparison of the experimentally-determined velocity distributions and core sizes, with the results of inviscid, laminar, and turbulent vortex models, is presented.