Flow Control on a Thick Airfoil Using Suction Compared to Blowing

Abstract

The effects of steady slot suction as a means of controlling separation on a blunt elliptical airfoil were investigated and compared to the effects of steady blowing applied to the same airfoil previously investigated. Slots whose width approaches 1% of the chord and are located downstream of the natural separation location generate the highest lift for a given dimensionless mass-flow coefficient C_Q. This holds true whether the flow separates near the leading edge due to high incidence or near the trailing edge due to the bluntness of the airfoil and is contrary to the observations made when blowing was used. Lift generated by suction through a moderately wide slot located downstream of the natural separation line depends only on C_Q, but if the slot is located upstream of the separation line it depends on Reynolds number as well. Contrary to separation control by blowing no deleterious effects were observed at low levels of suction regardless of the suction-slot location. Adding a wedge to the blunt trailing edge of this airfoil enhances the effectiveness of suction, whereas making blowing less effective at low momentum inputs thus increasing the gap between these two approaches to flow separation.