The Effect of Advance Ratio, Solidity, and Wake Interactions on a 2D Vertical Axis Turbine

Abstract

In recent years there has been an increased effort to utilize hydrokinetic devices to harvest energy from both wind and tidal flows. Vertical axis turbines utilization is of particular interest in tidal flows. A major disadvantage in vertical axis turbines is that they are less efficient than horizontal axis turbines. To increase the efficiency of the vertical axis turbines, 2D CFD simulations are completed in an effort to better understand the physics behind the operation of these turbines. Specifically, the effect of advance ratio, solidity, and wake interactions were investigated. Simulations were completed in OpenFOAM using the k-ω SST turbulence model at a nominal Reynolds number of 500,000 using a NACA 0015 airfoil. To simulate the motion of the turbine, Arbitrary Mesh Interfacing (AMI) was used. For all of the parameters tested, it was found that the geometric effective angle of attack seen by the turbine blades had a significant impact on the power extracted from the flow. The range of effective angles of attack was found to decrease as the advance ratio increased. In spite of this, a severe loss in the power coefficient occurred at an advance ratio of 2.5 during which the blade experienced dynamic stall. This effect was also seen when the number of turbine blades was changed to four, at a solidity of 1.08. Results indicate that wake interactions between subsequent blades have a large impact on performance especially when the wake interaction alters the flow direction sufficiently to create conditions for dynamic stall.