Hydraulic design validation of the suction intake of a vertical centrifugal pump station by use of Computational Fluid Dynamic (CFD) analysis

The correct operation of vertical centrifugal pumps is strongly dependent on the design of the entire pump intake system, which includes the suction sump and the associated piping. From the hydraulic point of view, the sump or pump intake design is one of the most critical aspect the designer is facing with: an incorrect sump dimensioning can determine the onset of detrimental fluid dynamic phenomena like pulsation, cavitation and a vortical activity which can easily lead to the appearance of undesired vibration of the entire pump structure. Basic guidelines for the sump and the intake pipeline design have been well established over the years and are now widely published. They include recommendations for the definition of the main sump dimensions, together with the minimum submergence as well as recommended typical velocities approaching the pump suction bell. When shape and dimensions are not standard, it is very often required to perform an experimental investigation of the sump characteristics with a scaled model to evaluate the hydraulic behavior of the intake system and, if necessary, provide indications for changes in the system layout to meet the required criteria. In the recent years, CFD has become a well established tool for the design validation of all pumps components. Nevertheless, numerical simulation applied to intake systems has not yet received the deserved attention, most probably due to the massive computational resources required for the modelization of complex intake structures. With the more extensive availability of powerful computers and advanced computational codes, this is not anymore an obstacle. In this respect, the numerical simulation can be seen as a realistic and more economical alternative to model testing. The paper presents an application of the CFD analysis to the hydraulic evaluation of a pump station intake. In the absence of a model test and thanks to a not complex geometry of the sump under investigation, the numerical results can be easily compared to the expected results obtained with the more traditional methods (i.e. Hydraulic Institute) for a basic validation of the numerical simulation. Eventually, the exercise claims to be a contribution to the rising debate on the applicability of numerical simulation to this kind of applications.