Abstract
Vertical Axis Wind Turbines (VAWTs) are characterized by complex and unsteady flow patterns resulting in considerable challenges for both numerical simulations and measurements describing the phenomena involved. In this study, a 3D Actuator Line Model (ALM) is compared to a 2D and a 3D Vortex Model, and they are validated using the normal forces measurements on a blade of an operating 12 kW VAWT, which is located in an open site in the north of Uppsala, Sweden. First, the coefficient power ( C P ) curve of the device has been simulated and compared against the experimental one. Then, a wide range of operational conditions for different tip speed ratios (TSRs), with λ = 1.84, 2.55, 3.06, 3.44, 4.09 and 4.57 were investigated. The results showed descent agreement with the experimental data for both models in terms of the trend and magnitudes. On one side, a slight improvement for representing the normal forces was achieved by the ALM, while the vortex code performs better in the simulation of the C P curve. Similarities and discrepancies between numerical and experimental results are discussed.
Highlights
A renewed interest in Vertical Axis Wind Turbines (VAWTs) has arisen from the current trend of wind energy industry aiming for large scale turbines in offshore farms [1,2,3]
During the numerical work with, the Actuator Line Model (ALM)-SK model revealed that the overestimated drag force will only give a notable contribution to the coefficient power (CP) and not the normal force, whose main contribution comes from the lift force
The presented models are able to reproduce the normal forces on a blade of an VAWT in an open site for a wide and diverse range of operational conditions, covering shallow to deep dynamic stall regime
Summary
A renewed interest in VAWTs has arisen from the current trend of wind energy industry aiming for large scale turbines in offshore farms [1,2,3]. The omni-directionality of VAWTs allow them to operate with incoming wind from any direction, this simplifies the mechanical design using a few moving parts without a yawing system and often excluding the pitching system. This is a relevant characteristic since a considerable part of failures on the HAWTs occurs in the yawing mechanism: Ribrant and Bertling [7] showed that for a typical HAWT in Sweden, the failure in the yawing systems represents the 13.3% of the total mean downtime per year. In Reference [8], Tavner et al
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