AMBIENT TURBULENCE INTENSITY EFFECTS ON THE CHARACTERISTICS OF WAKE DEVELOPMENT OF A MODEL WIND TURBINE AND A MATCHED POROUS DISC

2022-9-1
Öztürk, Buğrahan
This thesis study aims to observe the ambient turbulence intensity effects on the wake development of a model wind turbine and a matched porous disc. Comprehensive wind tunnel experiments are conducted in the wake of the model wind turbine and the porous disc up to 7 diameters downstream through two-dimensional two-component particle velocimetry. The wakes of the model wind turbine and the porous disc are investigated in terms of the mean flow field, turbulence, wake decay, and wake spreading characteristics. Three inflow conditions, namely uniform flow, passive grid flow, and boundary layer flow, are simulated in the test section of the wind tunnel. Furthermore, Proper Otrhagonal Decomposition analysis are carried out to examine the coherent structures of the wake of the both models, whose superposition form the mean wake flow. By comparing uniform inflow with low turbulence intensity and passive grid flow conditions, the findings demonstrate that even when operating at similar, high or low, freestream turbulence intensity levels, the wind turbine's mean wake flow field (both near and far wake) significantly differs from that of the porous disc. In addition, although the thrust coefficient is the same, the wake of the wind turbine recovers considerably faster than the wake of the porous disc. However, the findings further reveal that the characteristics of the porous disc at high freestream turbulence intensity and the characteristics of the model wind turbine at low freestream turbulence are extremely similar in the far-wake region. This shows that when employing porous discs to replicate wind turbines in wind tunnel research, care should be taken in selecting the ambient turbulence intensity level. Further wake measurements are performed under boundary layer inflow conditions by immersing both models into the boundary layer resulting in different ambient turbulence intensity levels and inflow velocity profiles. Results reveal that the far-wake characteristics of the model wind turbine and the porous disc cease to be comparable as both models are immersed in the boundary layer.

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Citation Formats
B. Öztürk, “AMBIENT TURBULENCE INTENSITY EFFECTS ON THE CHARACTERISTICS OF WAKE DEVELOPMENT OF A MODEL WIND TURBINE AND A MATCHED POROUS DISC,” M.S. - Master of Science, Middle East Technical University, 2022.