Study on the Secondary Flow in the Downstream of a Moving Blade Row in an Axial Flow Fan

Abstract

Experimental and theoretical investigations are carried out on the secondary flow in the downstream of a rotor row in a single stage axial-flow fan with a stator row ahead of the fan wheel. A five hole pitot tube was placed in the downstream of the fan wheel, and the relative flow field was measured for several hub ratios by traversing the tube over one blade spacing. An analysis is made of an incompressible, inviscid, but rotational flow through the stator row and the successive rotor row. The relative streamwise component of vorticity is obtained analytically in the downstream of the rotor row, and is used to calculate the secondary flow velocities. Discussions are made on the stream function of the secondary flow, the air outlet angle from the rotor row, the distribution of loss coefficients, the swirling flow rate of the secondary flow, and its kinetic energy. Hub ratio effects on these items are examined.