Unsteady Pressure Distribution inside a Cross-Flow Impeller

Abstract

The authors experimentally studied the characteristics of the flow around/inside a cross-flow fan, namely, a cross-flow impeller. In order to eliminate complicated influence of many casing factors, the impeller rotates in open space without any casings. As a result, at the singular aspect ratio L/D₂=0.6, at which the outflow rate Q₀ out of the impeller and the maximum vorticity ω_max attain the maximum values, the authors reveal minute fluctuating pressures on impeller's end wall. In some pressure measurements, the eccentric vortex inside the impeller is prevented to revolute by the insertion of a tongue, in order to consider the spatial structure of flow more precisely. The authors have confirmed that the influence of the tongue insertion is negligible. And, the authors confirmed such Reynolds-number effect as a time-mean pressure coefficient C_pmean decreases with increasing Reynolds number for Re ≤ 4.0×10³. Based on phase-averaging technique by the synchronised measurement of a impeller-rotation-counter signal, the pressure distribution inside the impeller shows that the minimum value is at θ =300deg.