Numerical and Experimental Studies on the Propulsion Performance of A Wave Glide Propulsor

This paper introduces a newly developed Unmanned Wave Glide Vehicle （UWGV）, which is driven only by extracting energy from gravity waves, and presents a comprehensive study on the propulsion performance of the UWGV＇s propulsor-Wave Glide Propulsor （WGP） in a regular wave. By simplifying the WGP as six 2D tandem asynchronous flapping foils （TAFFs）, a CFD method based on Navier-Stokes equations was first used to analyze the hydrodynamic performance of TAFFs with different parameters of non-dimensional wave length rn and non-dimensional wave height n. Then, a series of hydrodynamic experiments were performed. The computational results agree well with the experimental results when n〈0.07 and both of them show the thrust force and input power of the WGP are larger at smaller m or larger n. By analyzing the flow field of TAFFs, we can see that a larger m is beneficial to the forming, merging and shredding of the TAFFs＇ vortices; as TAFFs are arranged in tandem and have the same motions, the leading edge vortex and wake vortex of the TAFFs are meaningful for improving the thrust force of their adjacent ones.

NUMERICAL SIMULATION OF THE HYDRODYNAMIC PERFORMANCE OF AN UNSYMMETRICAL FLAPPING CAUDAL FIN

A comprehensive numerical simulation of the hydrodynamic performance of a caudal fin with unsymmetric flapping motion is carried out. The unsymmetrical motion is induced by adding a pitch bias or a heave bias. A numerical simulation program based on the unsteady panel method is developed to simulate the hydrodynamics of an unsymmetrical flapping caudal fin. A CFD code based on Navier-Stokes equations is used to analyze the flow field. Computational results of both the panel method and the CFD method indicate that the hydrodynamics are greatly affected by the pitch bias and the heave bias. The mean lateral force coefficient is not zero as in contrast with the symmetrical flapping motion. By increasing the pitch bias angle, the mean thrust force coefficient is reduced rapidly. By adding a heave bias, the hydrodynamic coefficients are separated as two parts： in one part, the amplitude is the heave amplitude plus the bias and in the other part, it is the heave amplitude minus the bias. Analysis of the flow field shows that the vortex distribution is not symmetrical, which generates the non-zero mean lateral force coefficient.

PREDICTION OF LOADING DISTRIBUTION AND HYDRODYNAMIC MEASUREMENTS FOR PROPELLER BLADES IN A RIM DRIVEN THRU-STER

This article presents an approach which employs a commercial Reynolds-Averaged Navier-Stokes（RANS）solver to predict the steady wake field and loading distributions for a rim driven thruster.Four different cases of propeller blades are chosen to be calculated with the presented method.The propeller blade radial circulation and chordwise circulation density distributions are analyzed.The maximum radial circulation is found at the blade tip,which is different from conventional shaft driven propeller.The numerical results indicate that there is no tip leakage vortex in rim driven propulors.But there exist the tip joint vortex and the root region vortex.Bollard characteristics are calculated by taking rim surface effect into account.From the predicted results the second case in this paper is selected as the final one to perform hydrodynamic experiment.The calculation results with empirical rim surface corrections are compared with the measurement.It shows that the developed numerical method can well predict hydrodynamic performances of the rim driven thruster.

NUMERICAL AND EXPERIMENTAL STUDIES OF INFLUENCE OF THE CAUDAL FIN SHAPE ON THE PROPULSION PERFORMANCE OF A FLAPPING CAUDAL FIN

This article presents a comprehensive study of the effects of the caudal fin shape on the propulsion performance of a candal fin in harmonic heaving and pitching. A numerical simulation based on an unsteady panel method was carried out to analyze the hydrodynamic performance of flapping caudal fins of three shapes （the whale caudal fin with the largest projected area, the dolphin caudal fin with the median projected area, and the tuna caudal fin with the smallest projected area）. Then, a series of hydrodynamic experiments for three caudal fin shapes were performed. Both computational and experimental results indicate that the tuna caudal fin produces the highest efficiency. However the mean thrust coefficient of the tuna caudal fin is the smallest. It is found that although the mean thrust coefficient for the tuna caudal fin is not large, the input power of the tuna caudal fin is also quite small. So the tuna caudal fin achieves a high efficiency.