Abstract
An open-source 2D Reynolds-averaged Navier–Stokes (RANS) simulation model was presented and applied for a laboratory-scaled cross-flow hydrokinetic turbine and a twin turbine system in counter-rotating configurations. The computational fluid dynamics (CFD) model was compared with previously published experimental results and then used to study the turbine power output and relevant flow fields at four blockage ratios. The dynamic stall effect and related leading edge vortex (LEV) structures were observed, discussed, and correlated with the power output. The results provided insights into the blockage effect from a different perspective: The physics behind the production and maintenance of lift on the turbine blade at different blockage ratios. The model was then applied to counter-rotating configurations of the turbines and similar analyses of the torque production and maintenance were conducted. Depending on the direction of movement of the other turbine, the blade of interest could either produce higher torque or create more energy loss. For both of the scenarios where a blade interacted with the channel wall or another blade, the key behind torque enhancement was forcing the flow through its suction side and manipulating the LEV.
Highlights
While the main goal of the study was to obtain insights into the physics behind the effect of blockage on torque production, the numerical model was first compared with experimental results to evaluate its reliability
In order to distinguish between the two effects, the power output of the twin turbine system was compared with the single turbine power performance at the same blockage ratio
After an iterative sensitivity analysis, the numerical model was compared with previously published experimental results and reached quantitative agreement in terms of turbine power performance around the peak after blockage correction
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. In a wind or water tunnel experiment, the interaction between a turbine and the tunnel walls is a widely known effect. The cross-flow turbine literature mostly concerns with the correction of the power output and similarity of the turbine wakes [1,2,3,4,5]. The differences in torque production created by confining the flow and the physics behind were not well studied. Understanding the hydrodynamic interaction between a turbine and a fixed wall is a firm foundation for exploring interaction between multiple devices in an array
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