Measurement of high solidity vertical axis wind turbine aerodynamic loads under high vibration response conditions

A series of full-scale experimental wind tunnel tests were performed to determine the aerodynamic loading behaviour on the airfoils of a high solidity, H-type, vertical axis wind turbine. During the course of this investigation, high amplitude vibration of the turbine was observed over a wide range of test conditions. The primary vibration excitation mechanism was resonance of the dominant whirling mode of the turbine with the operating blade pass frequency. In addition, for a significant number of test cases, resonance of the airfoil support struts at higher frequencies was also observed. This large vibration response resulted in conditions that made it difficult or impossible to measure the underlying aerodynamic loading. As a result, in order to gain a greater understanding of the aerodynamic loading, a vibration isolation methodology was developed to remove the effect of vibration from the measured aerodynamic forces on the blades. This included tests with two different support shaft end conditions over a range of flow velocities from 8 to 11m/s, and the use of band-stop filtering to remove residual small amplitude vibrations. In this way, an accurate and complete measurement of the aerodynamic loading on the turbine blades could be obtained to better understand the effects of dynamic stall and validate the results of numerical model predictions.