Unsteady Flow Simulations of an Over-the-wing Propeller Configuration

The aerodynamic integration effects of an embedded over-the-wing propeller at take-off conditions are discussed based on steady and unsteady Reynolds-averaged Navier-Stokes flow simulations. In contrast to the rotating blade and hub geometry, the steady computations utilized an actuator disk model with blade element theory enhancement to investigate the mutual influnce between installed propeller and wing with sufficient accuracy. A simplified high-lift geometry of this channel wing concept is compared to a conventional tractor configuration. While the general overthe-wing integration effects, such as lift-to-drag ratio improvement and deteriorated propeller efficiency, are already captured by inexpensive steady simulations, only unsteady computations with full propeller geometry reveal some important flow details. The most striking unsteady effect is the interaction of the blade tip vortex with the boundary layer of the wing which only occurs at the channel wing due to the close coupling. As a consequence the low momentum fluid detaches above the flap leading to a comparatively low lift coefficient.