SCALE EFFECTS IN CROSS-FLOW FANS - (EFFECTS OF FAN DIMENSIONS ON FLOW DETAILS AND THE UNIVERSAL REPRESENTATION OF PERFORMANCES)

Laser doppler velocimeter (LDV) measurements of velocity fields and the determination of static pressure distributions in the rotors of cross flow fans with good geometrical similarity but different dimensions have been performed, and the peculiar scale effects appearing in the flow details have been shown. The internal flow fields tend to be more active with increasing rotor size, and normalized velocity, vorticity, velocity fluctuations and pressure drops in the eccentric vortex increase as the fan dimensions increase. The mechanisms of generation and dissipation of vorticity in the eccentric vortex in rotor have been discussed, and it is suggested that the scale effects may be attributed to differences in the rate of diffusion of the circulation vortices in the recirculatory region. By analyzing the influences of Reynolds number and fan dimensions on performance curves, a new procedure for representing the performance of cross flow fans in a universal form has been proposed.