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

这个小型企业创新研究第一阶段项目将研究一种用于模拟泵中非稳定空化现象的创新配方。该公式基于可压缩的气液框架，该框架可以准确地模拟多相混合物中的声学，并可以扩展到考虑广义热力学效应。提出了一种新的空化模型，该模型基于跟踪与致密、气泡云团相关的表面积：这允许在连续统框架内实现详细的气泡动力学。多阶段配方将在商业CFD代码压缩中使用，该代码具有多元素非结构化框架，非常适合复杂的透平机械几何形状。第一阶段的工作将集中于验证单元问题中的非稳定空化程序，该程序将扩展到第二阶段计划中的三维泵几何形状。这项技术将适用于各种泵系统，这些泵系统必须在低流量、非设计流量和净正吸头(NPSH)条件下运行，在这些条件下，非定常流体动力和汽蚀的耦合可能会导致过度振动和损坏。目前设计工具在这种流态下的可靠性有限，这使得这一创新成为高能泵设计者的有用工具。商业潜力高能泵制造商必须认证他们的系统在非设计条件下运行。然而，在低NPSH水平下，非定常流动行为加上蒸汽体积的波动，在这种流动状态下可能会造成轻微的损害。因此，泵行业目前正在花费大量资源来更好地了解汽蚀不稳定性的形成。开发可消除或减轻云穴形成的创新设计将为新产品的营销和售后升级机会带来显著的竞争优势。然而，目前的设计工具，如经验关联式和一维分析，在这种流态下的可靠性有限。此外，对整个流型进行实验测试是不切实际的。这里提出的努力将通过提供一个工具来完善初步设计，以及纠正现有设计的问题来满足这些需求。此外，这里提出的创新技术将解决目前可用的商业CFD程序的缺陷：此类程序通常不能解析气液混合物中的声学，因为气液混合物的声速非常低，并直接影响流体动力学时间尺度。事实上，为了准确地模拟这种非定常多相问题，所提出的广义可压缩框架对于模拟流体动力压力波动和空化速率过程之间的耦合是必不可少的。该产品的潜在客户预计将是各种高能工业泵系统的美国制造商。

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.