Numerical simulation of vortex shedding in oscillatory flows

Krishna, Vikas (1995) Numerical simulation of vortex shedding in oscillatory flows. Masters thesis, Memorial University of Newfoundland.

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Abstract

Viscous forces that act on a body moving in a fluid may form a significant part of the total force acting on the body. The use of the linear potential-flow theory does not take into consideration the viscous effects that cause flow separation, skin-friction drag, and lift. Various methods have been developed and used to calculate the viscous forces numerically since Rosenhead's initial calculations. A review of the earlier work done in the area of vortex shedding and calculation of viscous flows is presented in chapter 1. Some vortex methods, that are commonly used, are described. One of these, the Discrete Vortex Method, is described in detail in chapter 2. This is demonstrated for a bluff body with sharp corners using the features of the Clement's model. However, this method does not simulate the effects of vorticity diffusion in the flow. Moreover, the body must also have sharp edges, which are taken to be the separation points. -- Another method, that does not impose such limitations, is the Vortex-In-Cell(VIC) Method. This is developed and first applied to study flows past a circular cylinder in order to validate the method with existing results in chapter 3. Conformal transformations coupled with this method enable us to study flows past bodies of other cross-sectional shapes. Various mappings are derived and developed to simulate flows past a variety of shapes. A fin was added on to the body contour to simulate the effect of a skeg in the case of boat-sections. The force coefficients, CD and CM, were calculated at different Keulegan-Carpenter numbers and verified for sections like a circle, a flat plate, and a square, in an oscillatory flow, with the results obtained by other workers. They were also calculated for a finned-circle, a section of a boat that is rounded and one that has hard chines. The theory and the method, the necessary modifications to the VIC method, and the simulation results are presented in chapter 4. A conclusion of the work done in the different chapters along with some comments are given in chapter 5.

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