Session: 06-15-01 Unsteady Hydrodynamics, Vibrations, Acoustics and Propulsion

Paper Number: 80803

80803 - Calculation of Thrust and Torque of a Tandem Propeller Using a Combined Vortex Lattice Lifting Line Method 

The method presented in this paper combines the advantages of an extended Goldstein approach and a vortex lattice method. This concept allows the fast and robust computation of propeller coefficients with a very low modelling effort. These properties make the presented method especially useful in the early design stage of a ship.

In the past years an extended Goldstein approach based on lifting line theory, which can predict the shape of the free vortex system of single and multi-component propulsors, has been developed at the Institute of Ship Design and Ship Safety. To make these improvements available for a vortex lattice calculation, a combined method has been created, which will be presented in the submitted paper.

The combined method avoids the time-consuming iterative determination of the free vortex system’s shape by using the extended Goldstein approach for this part of the calculation. For the subsequent computation of the thrust and torque coefficients of the tandem propeller two procedures are introduced. The first concept divides the calculation into two single propeller calculations in which the interactions between the two propellers are derived partly from the extended Goldstein approach and partly from the first vortex lattice calculation. This procedure allows the calculation of an open water diagram of the tandem propeller. Since the interaction of the two propellers is averaged circumferentially, it is not possible to calculate the behavior of the tandem propeller in the wake field of a ship or to account for the angular position of the propellers to each other. For this reason, the second procedure has been developed, in which the propeller interactions are investigated directly by including the complete tandem propeller in the vortex lattice part of the method. Since the used methods are based on potential theory, an empirical correction is used to account for frictional forces.

The accuracy of the combined method is evaluated by a comparison of the results with measured values from an open water experiment. This comparison shows that it is possible to achieve satisfactory agreement of results with the presented method.

Presenting Author: Andreas Buesken Hamburg University of Technology

Authors:

Andreas Buesken Hamburg University of Technology
Stefan Krueger Hamburg University of Technology