Experimental Study on the Characteristics of the Near Wake of a Rotating Flat Plate : 2nd Report, Influence of the Tip Clearance Flow with a Small Attack Angle

Abstract

We have experimentally investigated the influence of the tip clearance between a flat-plate-type blade and a duct surface on the flow characteristics around a single rotating blade. The setting angle of the blade was limited within the range where the leading edge separation did not occur over the whole blade span. The local attack angle of the main flow to the blade became smaller toward the tip; the leading edge separation, however, began near the blade tip. The separated zone gradually extended toward the boss of the rotor as the blade setting angle became larger. This is due to the fact that the low-energy fluid in the dead flow region of the wake of the blade is accumulated near the blade tip and it causes the leading edge separation there. A typical periodic fluctuation of the wake flow due to Karman vortex shedding from the trailing edge of the blade was observed in the intermediate region of the blade at any time if the reattached main flow did not separate up to the trailing edge on the suction surface of the blade.