Theoretical Computation of Boundary Layer Separation Point over an Impeller Vane Pressure Surface in Centrifugal Pump

Abstract

Centrifugal pumps are being used widely for many applications throughout the world. Lot of work is been carried out on performance improvements, hydraulic vane and volute profiles due to which considerable increase in the efficiency is been observed. It is very difficult to carry out the experimental tests to study the boundary layer behavior and its effect on the performance of the pump. Boundary layer separation plays a very important role in causing the secondary flows in the vane passage which affect the fluid flow path resulting in loss of effective energy transfer to the fluid by vane. Due to the centripetal force acting on the flow due to the curved path of the vane passage, separation of the boundary layer on pressure surface happens well before as compared to the flow separation occurring on the stationary vane surface. At the suction surface the flow is more concentrated hence the flow separation is difficult to occur. In this paper theoretical study of boundary layer behavior on the vane pressure surface is done and separation point is computed to find the occurrence of secondary flows from the separation point. The effect of centripetal force using Dean's equation for velocity distribution over the boundary layer, boundary layer thickness, momentum thickness, displacement thickness and Schlichting's form factor is studied and results are plotted to see the variation of these parameters.

Flow separation from the smooth-contoured streamlined surfaces

“…The flow separation occurs and it is an unavoidable consequence when steady flow turns into unsteady [1,17]. If motion of working medium takes place inside the channels, during the flow separation from its walls the hydraulic resistance increases dramatically [16,20], non-recoverable energy losses grow up, acoustic radiation increases and dynamic forces on all surfaces located in the area of moving medium rise sharply [2,10,18].…”