Development of Blade Element Momentum Theory for Unsteady Flow with Regard to the Dynamic Stall Phenomenon

Document Type : Research Article

Authors

1 Department of Aerospace Engineering, K.N. Toosi University of Technology, Tehran, Iran

2 Assistant Professor/ Aerospace Department /K.N.Toosi University of Technology

Abstract

The first step in turbine blade design is to select tip speed ratio. In this research, the optimum speed ratio is calculated with regard to the dynamic stall phenomenon. The dynamic stall imposes large amplitude loading on airfoil sections and since it occurs in turbine operating envelope in unsteady flow. The purpose of this study was to investigate the effect of unsteady flow with periodic oscillation on the performance of horizontal axis wind turbines. A dynamic stall model is implanted to analyze the static data obtained. Then, using this model and blade element momentum theory, the optimal tip speed ratio is calculated. Also, thrust and power coefficients are plotted in several different tip speed ratios. In addition to dynamic results, static results are plotted in power and thrust graphs. Comparison of these results shows how the dynamic stall causes the deviations of responses to static state. This phenomenon affects the efficiency by -3% as compared to the static stall. Also the optimum tip speed ratio increases in dynamic mode. In addition, time average diagrams of the drag coefficient show that the delay in separation starts approximately from the midpoints of the blade and reaches the maximum value at the root.

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References

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Amirkabir Journal of Mechanical Engineering
Volume 53, Issue 3
June 2021
Pages 1439-1456

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