Date

2021-05-25

Author

Abdulrahim, Anas
Akpolat, Tuğrul
Perçin, Mustafa
Uzol, Oğuz

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Analytical wake models are widely used in the industry due to their reasonably accurate prediction capability at low computational cost. In wind tunnel studies, wind turbine wakes are frequently modeled using porous discs that have uniform or non-uniform radial porosity (e.g. Camp and Cal [2016]). Amiri et al. [2019] compared wake model predictions to measurements for uniform and nonuniform porous discs. They showed that some model predictions agree well with measured wakes. Recently, we investigated the impact of inflow wind shear on the wake of a 0.12 m diameter nonuniform porous disc by successively immersing it into a boundary layer (Abdulrahim et al [2021]). Two-Dimensional Particle Image Velocimetry (PIV) measurements were performed on vertical (i.e. along the inflow shear direction) planes downstream of the disc at the disc center plane. It was shown that the wakes get strained and become asymmetric as expected due to the non-uniform inflow. Furthermore, a wake scaling methodology proposed by Chow et al [2005] was implemented to scale these non-uniform asymmetric wakes and it was shown that all data can be collapsed on to a single distribution. This scaling methodology is based on a scaling parameter β, which is the ratio of local shear strain to average shear strain within the wake. This parameter is used to obtain a velocity scale (Uβ-U0) and a length scale (δβ) for either side of an asymmetric wake (for a uniform inflow the wakes are symmetric and both sides of the wake produce a single streamwise distribution for Uβ and δβ). In this study, we investigate how these wake scaling parameters, Uβ and δβ, evolve within the disc wake and compare the experimental results with those obtained from Bastankhah and Porte-Agel [2014] wake model. The comparisons are made first for the flow outside the boundary layer, i.e. uniform inflow. For the cases when the disc is within the boundary layer, we first calculated the downstream wake profiles from the analytical model on horizontal planes with different inflow velocity values matching the local inflow velocity level calculated from the inflow shear. Then, combining the predicted minimum wake velocities on horizontal planes at the disc center, vertical profiles are generated to be compared to the PIV data. These distributions are in turn used to calculate the streamwise variations of Uβ and δβ, and results are compared to the ones obtained from porous disc experiments.

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https://hdl.handle.net/11511/99612

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Department of Aerospace Engineering, Conference / Seminar