11 Composite Overset Structured Grids

The use of composite overset structured grids is an effective means of dealing with a wide variety of flow problems that spans virtually all engineering disciplines. Numerous examples involving steady and unsteady three-dimensional viscous flow for aerospace applications exist in the literature. The literature also chronicles a host of applications of the approach in areas as diverse as biomedical fluid mechanics and meteorology. Many factors provide incentive for adopting the approach. A geometrically complex problem can be reduced to a set of simple components. Arbitrary relative motion between components of multiple-body configurations is accomplished by allowing grid components to move with six degrees of freedom in response to applied and dynamic loads. Limited memory resources can be accommodated by problem decomposition into appropriately sized components. Scalability on parallel compute platforms can be realized through problem decomposition into components (or groups of components) of approximately equal size. In many ways, a composite overset grid approach is similar to the so-called patched, or block-structured approach (see Chapter 13). However, even though differences between the approaches may appear slight (i.e., one requires neighboring grid components to overlap and the other does not), they are in fact substantial. In an overset approach, grid components are not required to align with neighboring components in any special way. Accordingly, the approach offers an additional degree of flexibility that is not available with patched grids. Steger [1992] observed that an overset grid approach assumes “... characteristics of an unstructured grid finite element scheme that uses large powerful elements in which each element is itself discretized.” Indeed, the approach should enjoy many of the grid generation freedoms commonly associated with unstructured grids, while retaining, on a component-wise basis, all of the computational advantages that are inherent to structured data. The maturation process for overset grid generation tools is ongoing. Historically, application scientists and engineers have used grid generation software designed for patched grids to generate required overset Robert L. Meakin