The simulation of the viscous flow around a cylinder by the random vortex method
Abstract
The ability to calculate the loads on cylindrical members is of great importance in offshore engineering. The random vortex method (RVM) is applied to simulate steady, uniform incident flow over a cylinder and the flow about a cylinder in a free surface wave field. Tent functions are used to model the vortex sheets at the boundary and a Rankine core function is used for the vortex blobs. Secondorder accurate time integration and random walk diffusion algorithms are used. One of the most difficult problems with the RVM is the computational requirements of the convection calculations. The exact solution to this problem involves O(N sup 2) calculations, where N is the number of vortex blobs. A highly accurate method based on series expansion is introduced that is capable of reducing the computational requirements to O(N sup 1.4). Simulations for the case of steady, uniform incident flow were made for Reynolds numbers of 4,000 to 95,000. Comparison was made with experiments and finite difference calculations for the case of Reynolds number 9,500. The observed flow structures agreed well with the simulated flow. Simulations of the wave flows was also successful. The predicted forces agreed with experimental results within 10 to 20 percent for a range of incident wave lengths and amplitudes. The simulated vorticity fields provided an interpretation of the typical shapes seen in experimentally derive force curves, in which the various regions could be associated with the degree of vorticity formation and shedding.
 Publication:

Ph.D. Thesis
 Pub Date:
 1986
 Bibcode:
 1986PhDT........19T
 Keywords:

 Cylindrical Bodies;
 Flow Distribution;
 Loads (Forces);
 Prediction Analysis Techniques;
 Series Expansion;
 Simulation;
 Viscous Flow;
 Algorithms;
 Errors;
 Random Walk;
 Reynolds Number;
 Waves;
 Fluid Mechanics and Heat Transfer