Boundary layer characteristics of the Miley airfoil at low Reynolds numbers

Abstract

An experimental study of the effect of boundary-layer transition on the performance of the Miley airfoil at Reynolds numbers below 6xl0 was conducted. Lift and drag measurements were taken using a twocomponent strain gage force balance over a range of Reynolds numbers from 7 x 10 to 3 x 10. Static pressure distributions on the surface of the airfoil were measured for Reynolds numbers up to 6xl0 5 . Smoke flow visualization was used at Reynolds numbers between 7 x 1Q and 5 x 10 in order to obtain a qualitative picture of boundary-layer transition and flow separation. Initial studies showed a large region of hysteresis in both lift and drag performance between Reynolds numbers of 7 x 10 and 1.5 x 10. The hysteresis loop varied in size but typically occurred between 10and 18-deg angle of attack and resulted in up to a 15% difference in lift coefficient and up to a 60% difference in drag coefficient. Stability of the hysteresis loop was found to be dependent on several factors, most important of which were freestream turbulence, acoustic excitation, and boundary-layer trips. The test section environment was documented to explain changes in boundary-layer performance under normal operating conditions. Finally, quantitative analysis of the boundary-layer performance was conducted with a hot-wire anemometer at 0-, 7-, and 13-deg angle of attack for a Reynolds number of 1.5X 10. Comparison of the data obtained during the different experimental phases provides a consistent picture of the boundary-layer performance and subsequent hysteresis loop. Changes in the testing environment were found to be the critical factors in variations of the experimental results. Documentation of the test environment is a prerequisite to the analysis of any test results at low Reynolds numbers.