FLUID FORCE MOMENT ON A CENTRIFUGAL IMPELLER SHROUD IN PRECESSING MOTION

Experimental results of fluid moment on a centrifugal impeller shroud in precessing motion are discussed based on the bulk flow model to elu cidate the fundamental flow mechanism. It is shown that the backshroud /casing clearance flow and the destabilizing fluid force moment can be simulated by the bulk flow model fairly well if the measured behavior of the resistance is correctly incorporated in the model. From the ca lculations with and without steady and unsteady wall shear stresses, t he unsteady component of the clearance flow is shown to be basically a two-dimensional inviscid flow induced by the change in the flow thick ness. The effects of the leakage flow rate and the resistance at the l eakage flow entry are discussed, paying attention to the steady tangen tial velocity of the leakage flow.