Aspect-Ratio and Reynolds-Number Effects on Short-Span Cross-Flow Impellers without Casings

The purpose of this experimental research is to clarify both the aspect-ratio effect and the Reynolds-number effect, especially for the flow of cross-flow impellers with shorter axes. Particle-image-velocimetry (PIV) technique and a hot-wire anemometer are used for measurements of flow velocity. The impeller rotates without any casings. The authors study two kinds of the impellers, that is, one with forward-cambered blades and the other with radial-flat blades. As a result, observing eccentric-vortex revolution by using hot-wire measurements and flow visualisations, the flow can be classified into three modes. According to this classification, the authors show flow-regime maps for both impellers. Using PIV results, the authors define outflow rate Q from the impeller. Outflow-rate coefficient C_Q is independent of the Reynolds number for both impellers. For the radial-flat-blade impeller, C_Q is not affected by aspect ratio L/D_2. But, for the forward-cambered-blade impeller, C_Q increases with L/D_2.