A Novel Approach to Simplification of NPSH(r) CFD Calculation

Abstract

Present work proposes approach that significantly shortens the calculation time for NPSH(r). This time is comparable with time for the head calculations. Most cavitation models take into account phase change, bubble dynamics, turbulent pressure fluctuations, etc. In this case multiphase flow model must be used. This work presents some simplifications, based on the physical nature of cavitation on the pump impeller, which significantly (10–50 times) reduces the calculation time of NPSH (r). The main idea of proposed procedure is to determine the liquid vapor (cavitation) zone simply from steady state calculation of one phase incompressible flow without taking into account multiphase effects. Based on absolute pressure distribution it is easy to determine areas with absolute pressure lower then saturated liquid vapor pressure for given liquid conditions. Consequently it is possible to consider the steady state location of liquid vapor (cavitation) on the impeller vanes. So this zone may simply be expelled from the flow domain. For many pump related cases, these zones are very close to cavitation areas, and give main impact on the head of the pump. Commercial Fluent 12.1.4 code is used for calculations. Proposed procedure for NPSH(r) calculation is in good agreement with test data for different types of pumps and may be used as a tool to shorten a design process for new pumps.