CHARACTERIZATION OF THE UNSTEADY LEAKAGE FLOW IN AN AXIAL FAN

The present work reports an experimental study of the leakage flow in a low-speed ring fan. Existing 2D Particle Image Velocimetry (PIV) measurements taken in a meridional plane in front of the rotor gap have been further processed and analyzed by means of the Proper Orthogonal Decomposition (POD). Three values of the dimensionless pressure rise across the rotor have been investigated. Namely, attention has been focused on the intermediate case, the one for which a strong radial oscillation in the leakage flow has been observed: the POD has shown that, at this condition, the leakage flow has a periodic character that is not correlated to the periodic blade passing. Moreover, such coherent motions have been found to promote turbulence transport at different radial positions, a behavior that was not observed for the periodic fluctuations related to the rotor. The present POD procedure can be therefore generally applied to turbomachinery flows to characterize their unsteady behavior beside the classical phase-averaging methods based on rotor related quantities. The present approach is novel for the leakage flow study.