Numerical Study And Analysis Of Pump Performance Parameters And Cavitation Effects In Centrifugal Pumps

Centrifugal pumps are commonly used in water, sewage, petroleum, petrochemical and other pumping systems. They are a sub-class of dynamic axisymmetric work-absorbing turbomachinery; sometimes the pump system may be required to operate over a wide flow range in some special applications. Thus, knowledge about off-design pump performance is a necessity. To some extent, pump flow behaviors depends on pump geometric parameters and working conditions such as the pump components dimensions and impeller rotational speed respectively. For instance, the increase in number of blades may give a positive effect to the pump head development within a certain range of values, but also may results in a detrimental effect not only to the pump performance but also to the pump physical state, when working beyond that safety range with different pump performance failures occurrence, cavitation among others. Therefore, it’s a responsibility for fluid machinery designers to pay a close attention to such pump performance parameters just at the device design stage. From the beginning, it was such a big challenge for design engineers to give out an accurate prediction of pump performance before sending the drawings to the manufacturing site. However, with the introduction of computerized design methods, to note with, Computational Fluid Dynamics(CFD), the design process became a bit relaxed, providing enough accuracy in terms of fluid machinery performance prediction. In order to get a better understanding of pump flow dynamics and related parameters, this project, through numerical simulations with a commercial CFD code ANSYS FLUENT 14.5, analyses the fluid flow through a centrifugal pump by changing its blades number and rotational speed under cavitating and non cavitating conditions. Under non cavitating conditions, with water at 25 degree Celsius as the working fluid, both parameters showed an increasingly better pump performance in terms of both Head and pressure patterns. Under cavitating conditions, with a mixture of water and water vapor as the working fluid, both parameters showed an increasingly worse performance in terms of developed pump head, as vapor phase volume fraction drastically augmented with both the increase of impeller rotational speed and blades number leading to an almost complete blockage of fluid flow at inter-blades flowing zones at each parameter’s higher value. Both parameters were found to be very influential when it comes to pump performance prediction and CFD was found to be a very reliable tool for centrifugal pump performance prediction.