Computational study of a lifting surface in propeller slipstreams

The high speed flow in the wake of the propeller also known as propeller wash, or simply propwash, can severely affect the aerodynamic forces on a lifting surface. Steady-state computational results for a symmetric SD8020 airfoil of unit chord in a propeller slipstream at a freestream Reynolds number of 100,000 are pre­sented in this paper. For the two-dimensional analysis, a propeller with a diameter to chord ratio of 1 was modeled as an actuator disk line with a pressure jump boundary condition varying from 1 to 4 lb/ft2. As compared with the clean configuration, the lift coefficient and drag coefficient increased by a factor of five and 25, respectively, for the strongest actuator disk line configuration. The two-dimensional lift curve remained linear throughout the angle of attack range from 0 to 12 deg, and aerodynamic stall was not observed for the computed cases. Three-dimensional simulations with a circular actuator disk and a rectangular span lifting surface with a semi-span of unit chord were executed. Due to the wall mirroring effect, the setup simulated a system with infinite propellers upstream of a lifting surface with infinite span. A strong spanwise variation of lift in the slipstream shear layer resulted in induced trailing vortices. The trailing vortices caused downwash on the sections within the slipstream flow and upwash on the sections located outside the slipstream which led to an early onset of stall on the outboard sections.