Computational Study of Large Eddy Structure of Flows past Bluff Body and Oceanic Topography

Abstract

Simulation method is developed for flows with large eddy structure past bluff body and oceanic topography and some new techniques and indications are devised for the elucidation of the complicated 3D vortical flow.The separating flow simulations are exectued by TUMMAC-VII method. About such kind of flow field the axes of vorticities vary extremely along the wake and are deformed in time. Though large eddy structure and dynamics of these flow are supposed to be related to momentum balance, they should be represented by using rotational invariants which make sense about momentum equation and by using isosurface of these quantities in 3D computer graphics to realize large eddy spatial structure and mechanics of complex vortical flow.So the separating flow is divided into the shear vortex flow and the streamwise vortex flow, which are represented by the Lamb vector and the Lamb scalar respectively, and are related to the Navier -Stokes equation, and are connected each other by the Lagrange identity. They are visualized by isosurfaces in 3D computer graphics.In another way the Laplacian of pressure and pressure dissipation are also shown in computer graphics to visualize vortex tube motions which appear in the wake past a sphere or some bluff bodies.The above method indicates angular relation between three vectors : velocity, vorticity and pressure gradient of the separating flow. Moreover the development of coherent structure of vortex flow is well described.This method is first applied to a flow past a sphere and its usefulness is confirmed for the elucidation of the large eddy coherent structure and mechanics of the separating flow. Secondly it is applied to the upwelling flow about complex geometries, and some interesting motions are elucidated such as vortex trap and tornado-like vortex motions.