RANS and Hybrid RANS-LES Simulations of an H-Type Darrieus Vertical Axis Water Turbine

Omar Mejia,Jhon Quiñones,Santiago Laín

doi:10.3390/en11092348

Omar Mejia, Jhon Quiñones + Show 1 more

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https://doi.org/10.3390/en11092348

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Abstract

Nowadays, the global energy crisis has encouraged the use of alternative sources like the energy available in the water currents of seas and rivers. The vertical axis water turbine (VAWT) is an interesting option to harness this energy due to its advantages of facile installation, maintenance and operation. However, it is known that its efficiency is lower than that of other types of turbines due to the unsteady effects present in its flow physics. This work aims to analyse through Computational Fluid Dynamics (CFD) the turbulent flow dynamics around a small scale VAWT confined in a hydrodynamic tunnel. The simulations were developed using the Unsteady Reynolds Averaged Navier Stokes (URANS), Detached Eddy Simulation (DES) and Delayed Detached Eddy Simulation (DDES) turbulence models, all of them based on k-ω Shear Stress Transport (SST). The results and analysis of the simulations are presented, illustrating the influence of the tip speed ratio. The numerical results of the URANS model show a similar behaviour with respect to the experimental power curve of the turbine using a lower number of elements than those used in the DES and DDES models. Finally, with the help of both the Q-criterion and field contours it is observed that the refinements made in the mesh adaptation process for the DES and DDES models improve the identification of the scales of the vorticity structures and the flow phenomena present on the near and far wake of the turbine.

Highlights

The high energy demand, the political instability of major oil-producing regions, the depletion of fossil fuel reserves and the environmental problems due to the continuing deterioration of the global ecosystems have raised concerns about the future of energy
With the help of both the Q-criterion and field contours it is observed that the refinements made in the mesh adaptation process for the Detached Eddy Simulation (DES) and Detached Eddy Simulation (DDES) models improve the identification of the scales of the vorticity structures and the flow phenomena present on the near and far wake of the turbine
The performance of the turbine and the flow dynamics were investigated through numerical simulation employing the Unsteady Reynolds Averaged Navier Stokes (URANS), DES and DDES turbulence models, all of them based on k-ω Stress Transport (SST)

Summary

Introduction

The high energy demand, the political instability of major oil-producing regions, the depletion of fossil fuel reserves and the environmental problems due to the continuing deterioration of the global ecosystems have raised concerns about the future of energy. With this perspective, renewable energies have come to play an important role in society in order to reduce or eradicate these problems. To transform the kinetic energy stored in the rivers and seas tidal currents into electrical energy, turbines are used, and these can be classified into two types, horizontal and vertical axis turbines. Darrieus turbines with straight blades, known as Type H turbines or Giromills, are the simplest and most popular among vertical axis turbines

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