A Lifting Line Theory for a Three-dimensional Hydrofoil

Prandtl’s lifting line theory was generalized to the lifting problem of a three-dimensional hydrofoil in the presence of a free surface. Similar to the classical lifting theory, the singularity distribution method was utilized to solve two-dimensional lifting problems for the hydrofoil beneath the free surface at the air-water interface, and a lifting line theory was developed to correct three-dimensional effects of the hydrofoil with a large aspect ratio. Differing from the classical lifting theory, the main focus was on finding the three-dimensional Green function of the free surface induced by the steady motion of a system of horseshoe vortices under the free surface. Finally, numerical examples were given to show the relationship between the lift coefficient and submergence Froude numbers for 2-D and 3-D hydrofoils. If the submergence Froude number is small free surface effect will be significant registered as the increase of lift coefficient. The validity of these approaches was examined in comparison with the results calculated by other methods.

Propeller Design for an Autonomous Underwater Vehicle by the Lifting-line Method based on OpenProp and CFD

A high-efficiency propeller can enable a long mission duration for autonomous underwater vehicles(AUVs).In this study,a new method with OpenProp coupled with computational fluid dynamics was developed to design a propeller for an Explorer100 AUV.The towed system simulation of the AUV was used to measure the nominal wake,and a self-propulsion simulation was used to measure the effective wake at the disc plane just in front of a propeller.Two propellers referring to the nominal wake(propeller 1)and effective wake(propeller 2)were designed with OpenProp and appended with the AUV for self-propulsion simulations,respectively.Through the numerical simulation of the AUV self-propulsion tests,the cruising velocity of AUV was obtained.The flow characteristics of the self-propulsion in pressure and velocity contours were also analyzed.The propeller designed with an effective wake improved the thrust,velocity,and efficiency by approximately 11.3%,6.7%,and 2.5%,respectively,as compared with those with a nominal wake.The cruising velocity of the final designed propeller for the Explorer100 AUV improved by 21.8%,as compared to that of the original propeller from the AUV free-running tests.

Integrated lifting line/surface panel method for optimal propeller design with consideration of hub effect

An optimal marine propeller design method is proposed,which integrates the lifting line and surface panel method and is characterized by the use of the surface panel method to take the hub effect into consideration.By developing an integrated approach instead of an iterative method for the calculation of the interaction between the hub and the designed blades,the hub effects on the optimal circulation can be accounted for throughout the theoretical design procedure.This new integrated method provides a fast and accurate enough method to model the straight forward hub surface,in the optimal propeller design.A systematic design procedure from the basic design inputs to the blade geometry determination is performed and the designed propellers are validated by the surface panel method and the RANS method.The design and analysis cases are considered by different approaches with comparison and validation.And a comparative study including different hub geometries is also performed to reveal the mechanism of the hub effect on the distributions of the propeller optimal loads.