9TH INTERNATIONAL SYMPOSIUM ON FLOW VISUALISATION, 2000 A PIV STUDY OF SEPARATED FLOW AROUND A 2-D AIRFOIL

In order to acquire experimental data on an airfoil at high angles of attack, wind tunnel tests were carried out. The wind tunnel tests were carried out at Re=1.25 · 106 (based on chord length) on a 2-D model with 0.45 m chord and 2 m span based on the FFA-W3-211 airfoil geometry (21 % thick). This airfoil is typically used in wind turbine blades. The purpose of the study was to examine the flow field and study the recirculating region around the airfoil. The present study was carried at 8 ◦ and 15 ◦ angle of attack, with more focus on the latter, by using three methods; static pressure measurement, oil flow visualisation and Particle Image Velocimetry (PIV). It was of particular interest to determine the position of the separation and the resulting data could than provide appropriate data for validation of computational numerical calculations (CFD) for separated flow cases. Based on the velocity vector field obtained by the PIV data, the velocity profile, boundary layer quan-tities and the backflow coefficients were derived. The backflow coefficient was then used as a criterion for separation. The position of separation for 15 ◦ angle of attack was determined in the PIV measurements to be at x/c=0.39±0.03, in the pressure measurements at x/c=0.40±0.05 and, somewhat subjectively, in the oil flow visualisation at x/c≈0.42. The complete report (FFA-TN-1999-52) in pdf-format and the test data in ascii-format are available on request, for comparison with numerical results [3].