Dr. Vineet Ahuja, Combustion Research and Flow Technology, Inc.
In recent years unstructured mesh techniques have become popular for CFD analysis of external aerodynamic type problems. The main advantages of such an approach include mesh generation over complex domains, grid adaptation in localized areas, and accuracy in efficiently identifying complexities in local flow physics. Here a hybrid unstructured methodology will be discussed to carry out simulations for predominantly internal flow problems such as turbomachinery applications. Issues related to skewness and other constraints of tetrahedral meshes are addressed in the context of propulsive flows that exhibit a rich variety of length and time scales, as well as interesting flow physics. The unstructured framework permits the generation of a contiguous grid without internal boundaries between different components of a complex turbomachinery/valve system, and provides good local resolution in regions where the flow physics becomes important. The increased numerical stability resulting from these factors coupled with the parallel solution framework yields an efficient solution procedure for complex flows. In order to encompass flow regimes with phase change such as commonly seen in cavitating flows, a generalized multi-phase formulation for fluids operating at temperatures elevated relative to their critical temperatures will be presented. The multi-element framework provides flexibility in resolving the gas-liquid interface and the associated physics related to the interfacial dynamics. The unstructured framework with the embedded multi-phase model is used to simulate cavitation in turbopumps and control valves for both conventional as well as cryogenic fluids.