Abstract
The two fans were designed with the span height of 7mm and 35mm to investigate the influence of the span height on the unsteady flow in a sirocco fan without a casing. The radial velocity oscillations were measured by hot wire probes, and the oscillating frequency and the phase delay of the radial velocity oscillation were obtained by using a fast fourier transform (FFT) analysis. The 3 or 4 peaks were observed in the experiment and the numerical calculation. The experimental result shows that the oscillating frequency and the number of rotating cells in the sirocco fan with the span height of 7mm are larger than those with the span height of 35mm. The rotating vortices caused by the backflow were found in the numerical results.
