CFD-Based Hydraulic Design and Manufacturing of a Multistage Low Specific-Speed Diffuser Pump

Abstract

A multistage low specific-speed diffuser pump was designed to achieve very good hydraulic performance with a newly designed integrated diffuser, crossover and return guide vane. The diffuser was designed using a continuous crossover design. The design space of this diffuser was limited because of the usage of a mechanical pump design from a similar existing pump. This paper presents the simulation-based design of this new pump and the role that simulation can play in the manufacturing process. A new diffuser has been designed to obtain optimum efficiency and to ensure that the pump will operate most of its time very close its best efficiency point. The new diffuser was designed using an approach where the diffuser vane was stretched to completely cover the area starting just behind the impeller trailing edge towards the eye of the next stage impeller. This means that the diffuser vanes should now convert velocity into pressure, guide the fluid to the next stage impeller eye while reducing the swirl and uniformizing the flow. The shape of the diffuser has been optimized using response surfaces that were created using Computation Fluid Dynamics (CFD). This way, a diffuser with a minimum amount of losses was obtained, due to smooth and gradual area changes of the waterway. The final design incorporating this diffuser was analyzed using steady-state CFD to create the full performance curve. The design was transferred into a real physical product by manufacturing it. The resulting casting of the diffuser component was scanned using a 3D scanner. The 3D model of the scan was used to make a comparison using CFD between the performance of the designed and the manufactured diffuser. This provided understanding in how deviations due to the manufacturing process influence the performance. Finally, the complete pump underwent a performance test and its results closely matched the performance as calculated using CFD.