Effect of Freestream Turbulence on Laminar Separation Bubbles and Flow Transition on a Low Reynolds Number Airfoil

摘要

The effect of freestream turbulence intensity on the laminar separation bubble and flow transition over an SD7003 airfoil was investigated. Measurements were performed for Reynolds numbers ranging from 60,000 to 250,000, various angles of attack and turbulence intensities between 0.05% and 0.99%. Boundary layers with a separation bubble were found to develop a turbulent boundary layer more rapidly than those without. The trends in the skin friction downstream of the peak corresponding to the development of a turbulent boundary layer were very similar for all turbulence intensities, suggesting the turbulent boundary layer forming downstream of transition was not significantly affected by the turbulence intensities investigated. The fluctuating velocity spectra showed that the increase in freestream turbulence intensity introduced sufficient energy to the laminar boundary layer to initiate transition before the flow was able to separate at an angle of attack of 4° but not at 8°.