Validation and comparison of turbulence models for predicting wakes of vertical axis wind turbines

Andrew Barnes,Ben Richard Hughes,Daniel Marshall-Cross

doi:10.1007/s40722-021-00204-z

Abstract

Vertical axis wind turbine (VAWT) array design requires adequate modelling of the turbine wakes to model the flow throughout the array and, therefore, the power output of turbines in the array. This paper investigates how accurately different turbulence models using 2D computational fluid dynamics (CFD) simulations can estimate near and far wakes of VAWTs to determine an approach towards accurate modelling for array design. Three experiments from the literature are chosen as baselines for validation, with these experiments representing the near to far wake of the turbine. Five URANS turbulence models were chosen due to their common and potential usage for VAWT CFD: models k–ω SST, k–ω SST LRN, k–ω SSTI, transition SST, and k–kl–ω. In addition, the lifting line-free vortex wake (LLFWV) model was tested as an alternative to CFD for the far turbine wake where it was appropriate for use. The results for turbulent kinetic energy and vorticity were compared for the first experiment, whilst streamwise and cross-stream velocity were used for the other two experiments. It was found that none of the turbulence models tested or LLFVW produced adequate estimations within the methodology tested, however, transition SST produced the closest estimations. Further adjustments to the methodology are required to improve accuracy due to their large impact on results including use of 3D CFD, adjustment of surface roughness, and inlet flow characteristics.

Highlights

Vertical axis wind turbines (VAWTs) are an alternative wind turbine design to the traditional horizontal axis wind turbine (HAWT) design
The largest deviations occur for positive vorticity at tip speed ratios (TSRs) = 2.0 with overestimations greater than 140% for most models, with the exception of transition SST which demonstrates its Condition turbulent kinetic energy (TKE) Normalise d Area k-ω SST k-ω SST LRN Transition SST k-kl-ω Experimen t
In the positive X region, the current study demonstrates a significantly reduced deviation from the experiment using k–ω SST and transition SST compared to Lam and Peng, and Rezaeiha, Montazeri, and Blocken’s use of the same models

Summary

Introduction

Vertical axis wind turbines (VAWTs) are an alternative wind turbine design to the traditional horizontal axis wind turbine (HAWT) design. VAWTs have some potential advantages including omnidirectionality, lack of necessity of a pitching mechanism, and increased performance for arrays (Dabiri 2011). The potential for higher power density arrays (Dabiri 2011) allows for greater utilisation of regions which demonstrate geographical advantage such as higher wind speeds or more suitable topography which would reduce levelised cost of energy. There are disadvantages such as lower power coefficient and a more complex basic design. These disadvantages may be hard to address as VAWTs present a difficult flow problem to model due to effects of dynamic stall and highly variable angle of attack of the blades, alongside the more three-dimensional nature of the flow and greater interactions between blades. Computational ability has increased and, accurately modelling this flow has

Methods

Results

Discussion

Conclusion