Numerical Study and Design Modification of Double Suction Centrifugal Pump

Abstract

In present time of highly developed engineering, there are various types of centrifugal pumps in the market. All are specialized in different applications. Double suction centrifugal pumps are used for high flow rates. They are also advantageous in balancing the axial thrust on the shaft. M/s Lubi Industries, Ahmedabad desired to manufacture double suction centrifugal pump with higher efficiency. The design parameters for the pump were 25 m head, 1708 kg/s discharge and specific speed of 5226. In the present study, 2/5th scaled down model of actual prototype was selected by using geometric similarities guidelines. The scaled down model was having 14 m head, 188 kg/s discharge at the same specific speed as that of prototype. The numerical simulations of 2/5th scaled down model were carried out using k-", SST and BSL Reynolds stress turbulence models at five flow rates varying from 0.74QBEP to 1.26QBEP . The numerical simulations were carried out using CFD package “Ansys CFX”. As boundary conditions, mass flow rate inlet was specified at semi volute suction inlet and static pressure opening was defined at casing outlet. From the analysis, in the original pump head, power input and efficiency were found as 7.06 m, 20.48 kW and 70.40 % respectively. The average percentage difference between numerical and experimental results was found as 4.64 %; which shows very good agreement between the two approaches. To improve the pump performance, different profiles of rib viz. convex rib, concave rib, NACA 2412 airfoil shaped rib and rectangular rib were attempted by numerical approach. Among various modifications, provision of rectangular rib was found better. After the modifications, head, power input and efficiency were found as 13.11 m, 32.11 kW and 83.05 % at BEP; which showed around 86 % rise in head, 57 % rise in power consumption and 18 % rise efficiency of pump.