Aerodynamic Pressure Measurements on a Rotating Wind Turbine Blade

Wind turbine generators commonly operate in either a fixed-pitch or variable-pitch mode. In variable pitch mode the angle of the blade is changed as the wind speed varies to maintain near optimum airfoil angle of attack and to regulate peak power. The more common fixed-pitch rotors do not change pitch angle to regulate peak power. Instead the blade is allowed to stall aerodynamically. This approach results in rapid relief of loads due to gusts, and is more reliable and cost effective. However, the designer must accurately understand the rotating blade stall behavior of the airfoil in order to predict turbine loads. To understand such stall behavior a test program, which uses specially designed instrumentation, has been conducted by the Solar Energy Research Institute (SERI). A microprocessor-controlled measurement system has been designed and built to make accurate measurements of low pressures on a rotating wind turbine blade. This Pressure System Controller (PSC) is capable of simultaneously operating four pressure scanners (128 channels total) while rotating on a wind turbine blade. Calibrations and purge sequences are performed automatically on all 128 channels while the turbine is rotating. Data are fed to a Pulse Code Modulation (PCM) data acquisition system and recorded on magnetic tape for later processing. A description of the test setup and instrumentation design is given along with example results. Recommendations for future work and changes in the design approach are discussed.