SBIR/STTR Phase I: A Compressible Gas-Liquid Framework For Simulating Cavitating Pumps

This Small Business Innovation Research Phase I project will study an innovative formulation for simulating unsteady cavitation phenomena in pumps. The formulation is based on a compressible gas-liquid framework that accurately models the acoustics in multi-phase mixtures, and may be extended to account for generalized thermodynamic effects. An innovative cavitation model based on tracking the surface area associated with dense, bubbly vapor clouds is presented: this permits the implementation of detailed bubble dynamics within a continuum framework. The multi-phase formulation will be available within a commercial CFD code CRUNCH, which has a multi-element unstructured framework and is ideally suited for complex turbomachine geometries. The Phase I effort will focus on validating the procedure for unsteady cavitation in unit problems that will be extended to three-dimensional pump geometries in the Phase II program. This technology will be applicable to a wide variety of pump systems that have to operate over a range of low, off-design flow rates and Net Positive Suction Head (NPSH)conditions, where the coupling of unsteady hydrodynamics and cavitation has the potential for causing excessive vibration and damage. The limited reliability of current design tools in this flow regime makes this innovation a useful tool for high-energy pump designers. Commercial Potential Manufacturers of high-energy pumps have to certify their systems for operation at off-design conditions. However, unsteady flow behavior coupled with fluctuating vapor volumes at low NPSH levels can result in significant damage in this flow regime. Hence, considerable resources are currently being expended by the pump industry to better understand the formation of cavitation instabilities. The development of innovative designs that eliminate or mitigate the formation of cloud cavitation will result in a significant competitive advantage for both marketing of new products as well as aftermarket upgrade opportunities. However, current design tools, such as empirical correlations and one-dimensional analyses, have limited reliability in this flow regime. Furthermore, experimental testing over the entire flow regime is impractical. The proposed effort here will address these needs by providing a tool for refining preliminary designs, as well as correcting problems with existing designs. In addition, The innovative technology proposed here would resolve the deficiencies of currently available commercial CFD codes: such codes typically do not resolve the acoustics within the gas/liquid mixture, which can have very low sound speeds and directly impact hydrodynamic time scales. Indeed for accurately modeling this unsteady multi-phase problem, the generalized compressible framework proposed is essential for simulating the coupling between hydrodynamic pressure fluctuations and the cavitation rate process. Potential customers for this product are anticipated to be U.S. manufacturers of a broad range of high-energy industrial pump systems.