Analytical Model for Ring-Wing Propulsor Thrust Augmentation

Abstract

A simple, accurate, reduced-order model is developed for predicting the maximum available thrust performance of subsonic ring-wing propulsors varying in shroud airfoil length, thickness, camber, and/or angle of attack relative to the centerline. The method, applicable to drones, aircraft, ships, and more, identifies the potential upper limit to the thrust augmentation available from hover to cruise, as well as those dominant geometric features contributing to its achievement and those factors limiting its attainment. It employs classic thin airfoil aerodynamic principles and is an extension and enhancement of two previous reduced-order models. Sensitivity studies are conducted of impacts on thrust augmentation from shroud-induced viscous effects, radial loading variations induced by the propeller, and losses due to propeller-induced swirl. The model’s efficacy is assessed using over 40 independently published experimental and state-of-the-art inviscid and viscous computational data sets for more than 20 different configurations. It is shown that the model’s algebraic solutions provide very good engineering estimates at all operating conditions from hover to cruise, thereby enabling rapid preliminary design of ring-wing-based systems. Additionally, the new model provides a means to establish maps of the practical thrust augmentation limits for ring wings, providing rational starting points for formal optimization studies.