Experimental investigation of the influence of solidity on the performance and flow field aerodynamics of vertical axis wind turbines at low Reynolds numbers


The performance of a VAWT is critically dependent on solidity, tip speed ratio and Reynolds numbers.

The regions of poor performance of a VAWT decrease with increases in solidity, wind speed (and so Reynolds number).

VAWTs with different solidities result in very different aerodynamics and including differences in vortex shedding.

Lower solidity results in earlier stalling and low lift resulting in low torque which results in lower turbine performance.


This paper shows the results of an experimental investigation into the effect of changes in solidity on the performance of a Vertical Axis Wind Turbine. Two VAWT configurations are used, one of solidity σ = 0.26 (chord C = 0.03 m) and the other with σ = 0.34 (C = 0.04 m). The turbine performance coefficient (Cp) was measured over a range of tip speed ratios and Particle Image Velocimetry (PIV) was used to determine the flow field around both turbine configurations.

Performance (Cp–λ) curves for the two VAWTs are compared at the same Reynolds numbers to investigate the effects of solidity alone on the performance and aerodynamics of each configuration. The higher solidity (σ = 0.34) VAWT attained a similar maximum Cp but with a narrower Cp–λ curve than the lower solidity VAWT. The performance differences between the two VAWT configurations at two tip speed ratios are explained in detail using PIV around both VAWT rotor blades. This allows the linking of detailed aerodynamics to the performance and it was shown that the generation and shedding of stall vortices started earlier on the lower solidity VAWT than the higher solidity VAWT, thus limiting the rotor efficiency.


  • Solidity;
  • Performance;
  • PIV;
  • VAWT;
  • HAWT

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