Load Component Analysis of a Quad-Rotor Wind Turbine

View Video Presentation: https://doi.org/10.2514/6.2022-1510.vid

A multi-rotor wind turbine consisting of 4 rotors arranged in a double-T configuration is put through a series of test cases to analyze the vibratory loads. The turbines are 4 x 1.5MW,70m rotor diameter turbines taken from the NREL WINDPACT 1.5-70 baseline model. The test cases include rigid booms and tower without tower and boom shadow, flexible booms and a rigid tower without tower and boom shadow, flexible booms and a rigid tower with tower and boom shadow, and flexible booms and tower with tower and boom shadow. The magnitudes of the vibratory loads for each case are found and the sources of the loads are determined. It is found that the inertial loads dominate the loads without tower and boom shadow. When the booms are flexible, the magnitudes of the vibratory loads from the left and right booms differ by nearly 2x due to an asymmetrical gyroscopic torque generated by the co-rotating rotors at the tips of the booms. The flexible booms also increase the magnitude of the loads up to 25x for the force in the thrust direction. When tower and boom shadow are implemented, the vibratory loads increase by up to 11x for the side force. Tower and boom shadow act as an impulse in the aerodynamic loading, increasing the higher frequency content of the load components. Under the effect of tower and boom shadow, the aerodynamic component of the loads becomes the largest component of the loads. The impact of shadow is decreased when the size of the shadow is decreased by changing either the boom’s aerodynamic shape or size, leading to a reduction of up to 66% in the magnitude of the loads when the boom is 60% of the baseline diameter. When the tower is flexible, there is interaction between the top and bottom rotors and yaw bearing loads. This leads to an increase in the magnitude of the loads of up to 3x for the side force.