An improved full wake alignment scheme for the prediction of open/ducted propeller performance in steady and unsteady flow
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For a long time, ducted propellers have been 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 can be found in many types of ships and offshore structures. This thesis introduces several improvements on the wake alignment model in the panel method to predict the performance of ducted and open propellers. The full wake alignment, which aligns wake panels based on the local flow velocity, is improved with an emphasis on the consideration of general incoming flow. Previously, the full wake alignment model is restricted to the case in uniform inflow and now is extended to be able to handle non-uniform and non-axisymmetric inflow. Proper ways of improving the numerical algorithm in the full wake alignment scheme are investigated. viii Wake alignment model for the ducted propeller is studied and improved with an emphasis on the duct paneling. In this thesis, two repaneling options on the duct and duct wake panels are introduced to improve the predicted propeller performance. Also, efforts have been given to the control points on the non-planar panels on the duct inner surface to predict the performance at lower advance ratios. The full wake alignment is also applied to duct wake to represent the behavior of trailing vorticity after the trailing edge of the duct. The wake sheet representing the trailing vortex of the duct is improved by aligning it with the local flow velocity as in the case of the blade wake. Correlations among the predicted results from the panel method and other methods, i.e. full-blown Reynolds Averaged Navier-Stokes (RANS) simulations, vortex lattice method (VLM), and experiments are presented.