Performance prediction and flow field calculation for airfoil fan with impeller inlet clearance

The performance prediction of an airfoil fan using a commerical code, STAR/ CD, is verified by comparing the calculated results with measured performan ce data and velocity fields of an airfoil fan. The effects of inlet tip cle arance on performance are investigated. The calculations overestimate the p ressure rise performance by about 10-25 percent. However, the performance r eduction due to tip clearance is well predicted by numerical simulations, M ain source of performance decrease is not only the slip factor but also imp eller efficiency. The reduction in performance is 12-16 percent for I perce nt gap of the diameter. The calculated reductions in impeller efficiency an d slip factor are also linearly proportional to the gap size. The span-wise distributions of phase averaged velocity and pressure at the impeller exit are strongly influenced by the radial gap size. The radial component of ve locity and the flow angle increase over the passsage as the gap increases. The slip factor decreases and the loss increases with the gap size. The hig h velocity of leakage jet affects the impeller inlet and passage flows. Wit h a larger clearance, the main stream moves to the impeller hub side and hi gh loss region extends from the shroud to the hub.