Ducted propellers have been, for a long time, a viable alternative of propulsion; due to their higher efficiency at high thrust coefficients, less sensitivity to the ambient flow, and more robust mechanical layout, than open propellers. Applications of ducted propellers or thrusters can be found in many types of ships, particularly in floating production, storage and offloading (FPSO) and liquid natural gas (LNG) hulls for maintaining a vessel's position.
In the 20th Offshore Symposium of Texas SNAME we presented a hybrid method which coupled a Vortex-Lattice Method (VLM) solver with a Reynolds-Averaged Navier-Stokes (RANS) to simulate the flow around ducted propellers.
In this work, a panel method is applied to the prediction of the performance of ducted propellers. A ducted propeller with a rectangular shape tip and a thruster with a blunt trailing edge duct are considered. The effects of viscosity on the duct are evaluated via coupling the method with an integral boundary layer solver. One significant feature of this method is the application of full wake alignment scheme in which the trailing vortex wake sheets of the blades are aligned with the local flow velocity by also considering the effects of duct and duct wake. Additionally, a procedure of repaneling the duct is simultaneously introduced to improve the accuracy of the method. The results from the improved wake model are compared with those from a simplified wake alignment scheme. At the same time, full-blown RANS simulations of the three dimensional problem are conducted. The propeller thrust and torque, and the blade pressures, predicted by the present panel method, using the improved wake alignment model, show very good agreement with experimental measurements, and with results from a hybrid method developed by the Ocean Engineering Group of UT Austin, as well as with full blown results from RANS solvers.