An industrial-type centrifugal-flow fan was instrumented and tested in order to obtain a fully detailed relative flow pattern at impeller discharge. Testing entailed investigation of both primary flows (jet-wake pattern and presence of return flows) and secondary flows (due to streamwise vorticity either from meridional curvature or rotation effects). In addition to conventional probing, a crossed hot-wire probe was employed in the tests. Ensemble-averaging the hot-wire signals made it possible to obtain the three-dimensional phase-averaged relative flow pattern at discharge by means of double positioning of the probe. Results show secondary-flow effects of appreciable magnitude interacting with primary flows (e.g., return flow in the hub region and variations in vortex structure and wake position with variations in flowrate).

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