Prediction of wipp data using a relaxed-wake potential flow method

In this study, experimental results of the Workshop for Integrated Propulsion Prediction are compared with the authors’ initial and revised predictions using a relaxed-wake potential flow method. Digitized anonymous Navier-Stokes CFD predictions submitted by other groups are also provided for comparison. The potential flow method consists of higher-order distributed vorticity elements that are used to model both the propeller and wing surfaces and wakes. Viscous effects are taken into account through profile drag estimation using tabulated airfoil data and an empirical nacelle model. Inherent shortcomings of the method for this application lie primarily in the implicit assumption of a 2-D lift-curve slope of 2π per radian and an overly simplistic stall model for the wing. Regardless, predictions of wing lift and drag of the propeller-wing system found using this method are similar in accuracy to the CFD submissions in the pre-stall region. Four suggestions are made for ways to improve predictions: more extensive propeller performance data for validation, quantification of wind-tunnel freestream turbulence levels and model surface roughness, careful attention to detail with respect to the test model geometry, and more information on uncertainty with respect to the book-keeping process for separating drag from thrust in force measurements.