Transient numerical simulation to investigate pressure fluctuation spectrum and deficit in the near wake of a horizontal axis wind turbine

Abstract

Wind energy becomes one of the promised solutions as alternatives of using fossil power energy in the upcoming decades. As pressure fluctuation and flow deficit in the near wake play a crucial role in predicting the turbine performance, the novelty in the current study focuses on a three dimensional (3 D) transient numerical simulation to investigate near wake characteristics of NREL phase IV wind turbine. Pressure fluctuation spectrum and wake deficit at four sections downstream the turbine are the main parameters studied as well as the flow streams and iso-surface characteristics. The mentioned parameters are studied at four sections: (0.25 D), (0.5 D), (0.75 D), and (1 D) of turbine diameter. The obtained results are compared with corresponding data from the NREL Phase IV experiments for validation purposes. Results show that the highest-pressure fluctuation spectrum would be at the nearest wake region, and, then it decreases periodically. Hub pressure spectrum density is much lower than that density for the turbine blade. The wake deficit profile shows that the deficit is developing with time at a rate equal to (0.115 rate per sec). In addition, it was found that the wake is recovered just (1 d) of the hub diameter while the blade wake deficit becomes the dominant after (0.75 D) of turbine diameter to cover the whole wake region. It was also found that the downstream distances should be extended more to resolve the whole wake recovery. The comparison with the tests measurements shows agreement between both the numerical and experimental works such that the error doesn't pass 4.3 %.

Keywords

• Wind turbine
• CFD
• Near wake
• Wake deficit
• Turbulence model
• Pressure fluctuation density