Wall Distance Module

The mesh deformation module presented in section 2 uses the distance of the grid points to the closest group boundary for the weighting of groups and for the blend­ing of deformations. The wall distances control the influence of different boundary groups on the deformation of a specific volume grid node.

There are different approaches for the computation of wall distances, for example based on partial differential equations, as seen in [11], based on a clever merging of the boundary points [13], or just a naive brute force algorithm, which compares each boundary node with every volume mesh node. The presented method, which was adopted from DLR’s TAU preprocessor, uses another algorithm. In TAU the wall distance is used for the application of certain turbulence models. The method is, like the mesh deformation module, embedded into an independent module for the simulation environment FlowSimulator.

The algorithm uses an advancing frontier approach. Every grid node n gets an additional parameter xnear [n], which saves the coordinates of the currently nearest boundary node. Then in every iteration step, each node compares the distance to its xnear-entry with the xnear values of its neighboring nodes and where required updates the xnear-value with a better value from a neighbor. Since the boundary nodes have the correct solution directly at the beginning, the solution for xnear for each node moves into the field node by node.

This so-called advancing front algorithm makes it possible that for certain (struc­tured) grids it would take only a few iteration steps to advance the correct solution for xnear into the interior of the grid.