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

这个小企业创新研究一期项目将研究一种创新的公式来模拟泵中的非定常空化现象。该公式是基于一个可压缩的气液框架，准确地模拟了多相混合物的声学，并且可以扩展到考虑广义的热力学效应。提出了一种创新的空化模型，该模型基于跟踪与密集气泡蒸气云相关的表面积：这允许在连续体框架内实现详细的气泡动力学。多相配方将在商业CFD代码CRUNCH中提供，该代码具有多元素非结构化框架，非常适合复杂的涡轮机器几何形状。第一阶段的工作重点是验证单元问题中的非定常空化过程，该过程将在第二阶段扩展到三维泵的几何形状。这项技术将适用于各种各样的泵系统，这些系统必须在低流量、非设计流量和净正吸压头（NPSH）条件下运行，在这些条件下，非定常流体动力学和空化的耦合有可能导致过度振动和损坏。当前设计工具在这种流动状态下的可靠性有限，这使得这项创新成为高能泵设计人员的有用工具。商业潜力高能泵的制造商必须证明他们的系统在非设计条件下运行。然而，在这种流动状态下，非定常流动行为加上低NPSH水平下波动的蒸汽体积可能导致不显著的损伤。因此，目前泵行业正在花费大量资源来更好地了解空化不稳定性的形成。开发能够消除或减轻云空化形成的创新设计，将为新产品的营销以及售后升级机会带来显著的竞争优势。然而，目前的设计工具，如经验关联和一维分析，在这种流动状态下的可靠性有限。此外，对整个流型进行实验测试是不切实际的。这里提出的工作将通过提供一种工具来改进初步设计，以及纠正现有设计的问题来解决这些需求。此外，本文提出的创新技术将解决目前可用的商业CFD代码的不足：此类代码通常不能解决气/液混合物中的声学问题，这可能具有非常低的声速并直接影响流体动力时间尺度。事实上，为了准确地模拟这一非定常多相问题，所提出的广义可压缩框架对于模拟动水压力波动与空化速率过程之间的耦合至关重要。该产品的潜在客户预计将是美国各种高能工业泵系统的制造商。

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 ofpump 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 auseful tool for high-energy pump designers.Commercial PotentialManufacturers 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 insignificant 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.