Simulation and Sensitivity Analysis of a Wing-Tip Mounted Propeller Configuration from the Workshop for Integrated Propeller Prediction (WIPP)

In this work, the turbulent flow field around a wing-tip mounted propeller configuration is simulated using the model and test conditions released by the Workshop for Integrated Propeller Prediction (WIPP). In particular, the unsteady Reynolds-averaged Navier-Stokes and enhanced delayed detached eddy simulations with Spalart-Allmaras turbulence model are performed in a time-accurate manner with the multi-zone sliding mesh technique in which the propeller is allowed to rotate while the wing and the nacelle remain stationary. Time-averaged pressure coefficients at six spanwise locations along the wing surface are shown to be in good agreement with the experimental data, including the two locations directly in the propeller slipstream. Numerical predictions on finer grids are found to capture the general shapes of the wake profiles well compared with experimental data from the wake survey, but the peak values are under-predicted on all wake profiles except for the swirl velocity. Moreover, there appears to be a shift radially inward indicating that the wake quantities, and the thrust in particular, do not extend beyond the propeller tip, as suggested by the experiment. The simulations on finer grids reveal two major noise sources of this wing-tip mounted propeller configuration, namely the turbulent wake and tip vortex generated by the propeller blades, both impinging upon the wing and nacelle surfaces as they convect downstream. Visualization of the surface pressure fluctuations reveals the noise footprints on this integrated propeller-wing system. In particular, the impingement of propeller blade tip vortices on the leading edge of the wing immediately below the nacelle is identified to be the dominant noise source. Making inroads into sensitivity analysis of the full propeller-wing assembly, an unsteady discrete adjoint approach based on algorithmic differentiation is applied to evaluate the surface sensitivity of an isolated WIPP propeller with respect to the mean thrust coefficient design objective.