VELOCITY-MEASUREMENTS AND NUMERICAL-CALCULATIONS OF FLOW-FIELDS IN AND AROUND SAVONIUS ROTORS

The flow fields in and around Savonius rotors at various overlap ratio s have been investigated to clarify the effect of overlap on the flow mechanisms. Measurements of phase-averaged velocity distributions were carried out using particle imaging velocimetry with a conditional sam pling technique, and the results were compared with numerical calculat ions by a discrete vortex method. The measured velocity distributions indicate clearly the effect of the overlap both on the flow through th e overlap and on the formation region of the vortices downstream of th e rotor. Although numerical calculations can predict the basic feature s of the variation of the flow field with rotor angle, the flow field pf a stationary rotor, especially at small rotor angles, is not well r eproduced in the calculations, suggesting that the assumptions of flow separation at the tips of the blades and the two-dimensionality of th e flow are invalid. However, the correlation with measurement is impro ved for the flow over a rotating rotor.