Abstract
The behavior of a wing boundary layer immersed in a propeller slipstream has been studied experimentally in wind tunnel tests and in flight. Airfoil surface static pressure measurements were made for time-averaged effects, and time-dependent measurements were made with hot-film anemometer sensors for the determination of instantaneous velocities. Vertical boundary layer traverses were made at fixed chord locations for the determination of velocity profiles and for values of the turbulence intensity. The boundary layer has a coherent, time-dependent cycle of transitional behavior, varying from laminar to turbulent. This layer shows similarities to those disturbed by high levels of external flow turbulence and to those in a relaminarizing environment. Profile drag coefficients determined from the time-dependent ensemble-average velocity profiles for the freewheeling propeller case show the drag in the propeller slipstream varies from the undisturbed laminar value to a value less than that predicted for fully turbulent flow. Drag values determined from the low Reynolds number thrusting propeller case in the wind tunnel indicate that the effects of the slipstream are to enhance the stability of the boundary layer and to reduce the drag coefficient in the laminar portion of the slipstream cycle below its undisturbed value.
Howard, Richard Moore (1987). An investigation of the effects of the propeller slipstream on a wing boundary layer. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -26944.