PIV measurements and computational study of a 5-inch ducted fan for V/STOL UAV applications

Ducted fan vertical/short take-off and landing (V/STOL) uninhabited aerial vehicles (UAV) are popular because of their capacity of offering a higher static thrust/power ratio for a given diameter than open propellers. They are also known as camera/antenna carrying or sensor positioning devices. Because of their complicated missions, they need to be capable of flight in a broad range of atmospheric conditions. In forward flight, the performance of these vehicles is poor because of the distorted inlet flow. The present experimental study uses a planar particle image velocimeter (PIV) system to investigate the near duct aerodynamic performance in hover and forward flight condition. High resolution PIV measurements provide reliable aerodynamic measurements forming a validation basis for further analytical and computational design studies. A radial equilibrium based fan aerodynamic model in combination with angular momentum conservation principle and energy equation is effectively integrated into a three-dimensional RANS based computational system. PIV measurements and computational predictions of mean flow near the fan inlet plane are in very good agreement at hover conditions. The aerodynamic modifications due to fan inlet flow distortions in forward flight regime are clearly displayed in PIV results.