A Reduced Order Model to Predict Transient Flows around Straight Bladed Vertical Axis Wind Turbines

Soledad Le Clainche,Esteban Ferrer

doi:10.3390/en11030566

Abstract

We develop a reduced order model to represent the complex flow behaviour around vertical axis wind turbines. First, we simulate vertical axis turbines using an accurate high order discontinuous Galerkin–Fourier Navier–Stokes Large Eddy Simulation solver with sliding meshes and extract flow snapshots in time. Subsequently, we construct a reduced order model based on a high order dynamic mode decomposition approach that selects modes based on flow frequency. We show that only a few modes are necessary to reconstruct the flow behaviour of the original simulation, even for blades rotating in turbulent regimes. Furthermore, we prove that an accurate reduced order model can be constructed using snapshots that do not sample one entire turbine rotation (but only a fraction of it), which reduces the cost of generating the reduced order model. Additionally, we compare the reduced order model based on the high order Navier–Stokes solver to fast 2D simulations (using a Reynolds Averaged Navier–Stokes turbulent model) to illustrate the good performance of the proposed methodology.

Highlights

Vertical axis wind turbines for power generation, known as H-rotors, present complex flow phenomena associated with the blades operating in an inherently unsteady stream
We develop a reduced order model to represent the complex flow behaviour around vertical axis wind turbines
We have developed a reduced order model (ROM) to simulate and predict the behaviour of the flow around vertical axis turbines in a turbulent regime

Summary

Introduction

Vertical axis wind turbines for power generation, known as H-rotors, present complex flow phenomena associated with the blades operating in an inherently unsteady stream. These turbines consist of airfoil shaped blades that generate lift to drive a shaft, which is linked to a generator. The simulation and prediction of the temporal evolution of flows around vertical axis wind turbines is extremely difficult This difficulty is caused, on the one hand, by the above-mentioned blade motion, which leads to unsteady flow features and dynamic effects, and to the turbulent flow regime in which these devices operate (i.e., high Reynolds numbers). The disparity of scales increases with the Reynolds number and its simulation without modelling (direct numerical simulation) becomes prohibitive at flow conditions of industrial relevance, such as when simulating wind turbines

Methods

Results

Conclusion