VISCOUS FLOWFIELD BASED ON DISCONTINUOUS BOUNDARY ELEMENT METHOD AND VORTEX METHOD

The two-dimensional, three-dimensional viscosity and incompressible flow fields are simulated bases on a combination application of discontinuous boundary element method and vortex method in our present study. Discrete vortex elements are used to analogue the vorticity generation, accumulation and transport mechanisms of the unsteady separated flow fields. And it decomposes the computing domain into an interior domain of vortex blobs and a thin numerical boundary layer of vortex sheets. The convection and stretch of the vortical field is imitated by Lagrangian vortex method, and the random walk method is adopted to describe the diffusion process of the vortical field. Additionally, vortex element's vortical velocity is calculated by generalized Biot-Savart law, while discontinuous boundary element method is used to compute potential velocity. To avoid the discontinuous of normal velocity, all nodes of discontinuous boundary element are selected at smooth boundary. Since a large scale boundary element equation set with a nonsymmetrical coefficient matrix should be solved, the present study import a pre-conditioning the generalized minimum residual (GMRES) iterative algorithm, which takes full advantage of the boundary element method. Moreover, regularization algorithm that applies at interior points close to the boundary, which the nearly singular surface integrals are transformed into a series of line integrals along the contour of the element, help to eliminate the unacceptable results of potential velocity and velocity gradient in potential calculation. The accuracy of present method is verified in both examples of two-dimension and three-dimension flow field calculation, as well as the significant increased simulation precision and efficiency.