Numerical simulation of tip clearance flow in semi-open impeller pump

Semi-Open impellers are commonly used for handling fluids with abrasive particles. These impellers have back shroud and the blades do not have support front front shroud. The designer proposes standard clearance to allow free rotation of impellers in stationary casing. Design clearances are difficult to maintain during manufacturing as it calls for special manufacturing process. It is well established in experiments that both head and efficiency decrease with increase in tip clearance and are quite sensitive to rather small change in clearance. It was planned to carry out numerical experiments with such geometry and bring out effect of varying tip clearance on overall performance of pumps with semi-open impellers. In CFD analysis mostly pumps are analyzed with enclosed impeller as rotating component with stationery casing. The meshing of the tip clearance area was a matter of concern. This is overcome using commercial code CFX-Bladegen and CFX-Turbogrid software and good quality mesh of the impeller was prepared. The paper describes the numerical simulation of tip clearance in semi-open impeller pump. The flow pattern showing clearance vortices associated with tip clearance are brought out. Then effect of clearance on the overall performance of pump is established by varying tip clearance.