Fluid dynamics analysis of a counter rotating ducted propeller

The use of ducted propellers is common in VTOL UAV design. The presence of a duct improves propeller efficiency, provides protection and improves safety. The aim of this paper is to employ a sensitivity study for the total thrust of a ducted twin counter-rotating propeller system design for UAV applications using computational fluid dynamics. Two factors were investigated: propeller spacing and difference between blades pitch angle. Using 4 discrete values for both factors, 16 designs were analyzed and evaluated. The same approach was used for an equivalent unducted propeller system to assess the influence of the duct. A ducted twin counter-rotating propeller system was modeled in ANSYS CFX. Shear Stress Transport (SST) turbulence model was used for steady state simulations. An unstructured mesh with prism boundary layers was generated for the computational domains. It was found that the total thrust of both open and ducted counter-rotating propeller is highly dependent on the difference between blade pitch angles and propeller spacing. In terms of total thrust, the presence of a duct did not always improve system performance of counter-rotating propellers