Performance and aerodynamic braking of a horizontal-axis wind turbine from small-scale wind tunnel tests

In the public domain.. Prepared for NASA-Lewis Research Center Grant No. NSG-3277. Date of General Release: July, 1987Wind tunnel tests of three 20-inch diameter, zero-twist, zero-pitch wind turbine rotor models have been conducted in the WSU 7' x 10 1 wind tunnel to determine the performance of such rotors with NACA 23024 airfoil and with NACA 64 3-621 airfoil sections. Aerodynamic braking characteristics of a 30% span, 30% chord vented aileron configuration were measured on the NACA 23024 rotor. Surface flow patterns were observed using fluorescent mini-tufts attached to the suction side of the rotor blades. Experimental results with and without aileron are compared to predictions using airfoil section data and a momentum performance code. Results of the performance studies show that the 64 3 -621 rotor produces higher peak power than the 23024 rotor for a given rotor RPM. Analytical studies, however, indicate that the 23024 should produce higher power. Transition strip experiments show that the 23024 rotor is much more sensitive to roughness than the 643 -621 rotor. These trends agree with analytical predictions. Results of the aileron tests show that this aileron, when deflected, produces negative torque at all positive tip-speed ratios. In free-wheeling coastdowns the rotor blade stopped, then rotated backward at a tip-speed ratio of -0.6. Results of the tuft studies indicate that substantial spanwise flow develops as blade stall occurs at low tip-speed ratios.Prepared for NASA-Lewis Research Center Grant No. NSG-3277 NASA Technical Monitor:' J.M. Savin