AN EXPERIMENTAL INVESTIGATION OF BLADE ELEMENT THEORY FOR WIND TURBINES .1. MEAN FLOW RESULTS

This paper describes an investigation of blade element theory, which is commonly used to describe the flow through wind turbine blades. A two-bladed model turbine was shrouded by a constant-diameter pipe. The tip clearance was sufficiently small to minimise and localise the tip clearance losses. By passively heating the wake of one of the turbine supports, it was found that supports did not produce any significant circumferential non-uniformity in the mean axial and circumferential velocities. These velocities were measured using a conventional three-hole yawmeter and an X-probe hot-wire anemometer. The agreement between the two methods was good. The turbine's power output was also determined by two independent methods; again with good agreement. The major finding was that blade element theory underestimated the power contribution as a function of radius wherever the local angle of attack exceeded the angle that gives the maximum lift/drag in two-dimensional flow. Several possible causes of the discrepancy are discussed.