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CFD modelling investigation of a straight-blade vertical axis wind turbine
Abstract
Many attempts have been carried out in the past few years to build a general understanding of the straight blade vertical axis wind turbine aerodynamics. For this purpose many models have been developed. These models may be classified into four main categories: momentum, vortex, cascade and computational fluid dynamic based modelling. The computational fluid dynamics modelling has become more favourable due to the modelling aerodynamical complexity involved in the other modelling approaches. This approach has become more feasible in the last few years as the computational power has been significantly improved by the development of high performance computers. However, there has not been enough investigations on computational fluid dynamics simulations in the application of straight blade vertical axis wind turbines in the literature. This paper focuses on the computational fluid dynamics modelling aspects and their effects on the prediction accuracy of vertical axis wind turbines performance.
... In addition, the losses resulted in by the 3D effects are not considered. As a result, the power coefficient produced is expected to have a value higher than those obtained experimentally (Almohammadi et al. 2011). ...
Providing high starting torque and efficiency simultaneously is a significant challenge for vertical axis wind turbines (VAWTs). In this paper, a new approach is studied in order to modify VAWTs performance and cogging torque. In this approach, J-shaped profiles are exploited in the structure of blades in which by eliminating the pressure side of airfoil from the maximum thickness toward the trailing edge. This new profile is a new type of VAWT airfoil using the lift and drag forces resulting in the better performance at low TSRs. To simulate the flow fluid of the VAWT along with J-shaped profiles originated from NACA0018 and NACA0030, a two-dimensional computational analysis is conducted. The Reynolds Averaged Navier-Stokes (RANS) equations are closed using the two-equation Shear Stress Transport (SST) turbulence model. The main goal of this study is to investigate the effects of J-shaped straight blade thickness on the performance characteristics of VAWT. The results obtained indicate that opting for the higher thickness in J-shaped profiles for the blade sections leads the performance and cogging torque of VAWT to enhance dramatically.
This paper numerically investigates the effect of the trailing edge profile on the performance of the straight-blade vertical axis wind turbine (SB-VAWT). In a 2-D cross-section of the SB-VAWT model, four trailing edge profiles are investigated, namely sharp, rounded, S-blunt, and R-blunt. The numerical investigation is based on the unsteady Reynolds averaged Navier-Stokes (URANS) equations combined with the transition shear stress transport (SST) model in order to account for the transition in the boundary layer in the vicinity of the airfoils. It has been found that the trailing edge profile may play a significant role in improving the turbine performance and should be accurately accounted for in the design process of the SB-VAWT.
This paper use the Fluent software to calculate the flow field of the vertical axis wind turbine. The results got were almost agreeable with the experimental data. The results were much better agreeable with the experimental data when the TSR was larger than 1 .So it can be used as the fast and lower costing estimated tools for the vertical wind turbines.
This paper numerically investigates four methods, namely mesh refinement, General Richardson Extrapolation (GRE), Grid Convergence Index (GCI), and the fitting method, in order to obtain a mesh independent solution for a straight blade vertical axis wind turbine (SB-VAWT) power curve using computational fluid dynamics (CFD). The solution is produced by employing the 2D Unsteady Navier–Stokes equations (URANS) with two turbulence models (Shear Stress Transport (SST) Transitional and ReNormalized Groups (RNG) κ − ɛ models). The commonly applied mesh refinement is found to be computationally expensive and not often practical even for a full 2D model of the turbine. The mesh independent power coefficient produced using the General Richardson Extrapolation method is found to be encouraging. However, the Grid Convergence Index may not be applicable in mesh independency tests due to the oscillatory behaviour of the convergence for the turbine power coefficient. As an alternative, the fitting method shows a good potential for the predicting of the mesh independent power coefficient without the necessity to consider a massive number of meshes.
The flow around straight blade vertical axis wind turbines is typically complex at low tip speed ratios (TSR < 2). In this paper, the turbulence models which are based on the assumption of fully developed turbulent flow, such as S-A, RNG κ-ε and SST κ-ω have been investigated in comparison to the SST transitional model (both with and without curvature correction) to account for the laminar-turbulence transition. The investigation is based on the 2D unsteady Reynolds averaged Navier–Stokes (URANS) equations using a sliding mesh technique. It has been found that applying turbulence models based on the assumption of fully developed flow shows significant differences in velocity magnitude if the flow is under stall condition or wake effect compared to the transitional model. Also, the predicted flow structure in the vicinity of the stalled airfoils using different types of turbulence models is found to be different compared to the un-stalled airfoils where no significant differences in the flow field have been observed. In the wake region, the flow varies less significantly compared to the stalled airfoils.
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