Browsing by Subject "Ducted propeller"

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An improved full wake alignment scheme for the prediction of open/ducted propeller performance in steady and unsteady flow
(2017-09-15) Kim, Seungnam; Kinnas, Spyros A.
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.
An improved panel method for the prediction of performance of ducted propellers
(2015-08) Fan, Hongyang; Kinnas, Spyros A.; Tian, Ye
An improved perturbation potential based lower order panel method is applied to the three dimensional problems of flow around ducts and ducted propellers. One significant development 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. A process of repaneling the duct is simultaneously introduced to improve the accuracy of evaluation of the method. The results from the improved wake model are compared with those from a simplified wake alignment scheme (PSF-2 type scheme). At the same time, full-blown RANS simulations of the three dimensional problem are conducted. The forces, i.e. thrust and torque on the propeller predicted by the present panel method under the improved wake alignment model show good agreement both with experimental measurements, a hybrid method developed by the Ocean Engineering Group of UT Austin, and the full blown RANS simulations. Moreover, detailed pressure distribution on the blades and duct are compared among the various methods. The interactive method which couples the lower order panel method with a two dimensional boundary layer solver through a wall transpiration model is also introduced. An assumption of two dimensional flow is made on the individual stations of a three dimensional geometries and the coupling is applied in a stripwise manner by including the interaction effects from other strips. The interactive method is then validated through the cases of bare ducts and ducted propellers. An important improvement is also made on the extension scheme for hydrofoils and propeller blades with blunt trailing edge. A more physical criterion has been established for determining the location of cut planes or the starting points of the extension. The extension scheme is applied to both axisymmetric problems and fully three dimensional problems. Correlations of results with experimental measurements and RANS simulations are presented.
An improved viscous-inviscid interactive method and its application to ducted propellers
(2013-08) Purohit, Jay Bharat; Kinnas, Spyros A.
A two-dimensional viscous-inviscid interactive boundary layer method is applied to three dimensional problems of flow around ducts and ducted propellers. The idea is to predict the effects of fluid viscosity on three dimensional geometries, like ducts, using a two-dimensional boundary layer solver to avoid solving the fully three dimensional boundary layer equations, assuming that the flow is two-dimensional on individual sections of the geometry. The viscous-inviscid interactive method couples a perturbation potential based inviscid panel method with a two-dimensional viscous boundary layer solver using the wall transpiration model. The boundary layer solver used in the study solves for the integral boundary layer characteristics given the edge velocity distribution on the geometry. The viscous-inviscid coupling is applied in a stripwise manner but by including the interaction e ffects from other strips. An important development in this thesis is the consideration of eff ects of other strips in a more rational and accurate manner, leading to improved results in the cases examined when compared to the results of a previous method. In particular, the effects of potentials due to other strips arising out of the three dimensional formulation are considered in this thesis. The validity of assuming two-dimensional flow along individual sections for application of viscous-inviscid coupling is investigated for the case of an open propeller by calculating the boundary layer characteristics in the direction normal to the assumed direction of two-dimensional flow from data obtained by RANS simulations. Also, a previous method which models the flow around the trailing edge of blunt hydrofoils has been improved and extended to three dimensional axisymmetric ducts. This method is applied to ducts with blunt and sharp trailing edges and to a ducted propeller. Correlations of results with experiments and simulations from RANS are shown.