Simulation of flow over double-element airfoil and wind tunnel test for use in vertical axis wind turbine

Prasad Chougule,Søren R K Nielsen

doi:10.1088/1742-6596/524/1/012009

Abstract

Nowadays, small vertical axis wind turbines are receiving more attention due to their suitability in micro-electricity generation. There are few vertical axis wind turbine designs with good power curve. However, the efficiency of power extraction has not been improved. Therefore, an attempt has been made to utilize high lift technology for vertical axis wind turbines in order to improve power efficiency. High lift is obtained by double-element airfoil mainly used in aeroplane wing design. In this current work a low Reynolds number airfoil is selected to design a double-element airfoil blade for use in vertical axis wind turbine to improve the power efficiency. Double-element airfoil blade design consists of a main airfoil and a slat airfoil. Orientation of slat airfoil is a parameter of investigation in this paper and air flow simulation over double-element airfoil. With primary wind tunnel test an orientation parameter for the slat airfoil is initially obtained. Further a computational fluid dynamics (CFD) has been used to obtain the aerodynamic characteristics of double-element airfoil. The CFD simulations were carried out using ANSYS CFX software. It is observed that there is an increase in the lift coefficient by 26% for single-element airfoil at analysed conditions. The CFD simulation results were validated with wind tunnel tests. It is also observe that by selecting proper airfoil configuration and blade sizes an increase in lift coefficient can further be achieved.

Highlights

Various types of vertical-axis wind turbines (VAWTs) have been suggested
The most wellknown include the Darrieus-type egg beater-shaped VAWT invented in 1931 [1], the Savonius type VAWT invented in 1929, and the H-rotor type design, which appeared after research activity from 1970 to 1980 in the UK
Darrieus VAWTs have recently been documented as an alternative solution for small power production [2]-[3]

Summary

Introduction

Various types of vertical-axis wind turbines (VAWTs) have been suggested. The most wellknown include the Darrieus-type egg beater-shaped VAWT invented in 1931 [1], the Savonius type VAWT invented in 1929, and the H-rotor type design, which appeared after research activity from 1970 to 1980 in the UK. The power coefficient of a conventional VAWT was improved by using a double-element airfoil in the blade design. In this context , the S1210 and S1223 airfoils have proven to be better than the symmetric or non-symmetric NACA airfoils [12] They were originally designed to obtain high lift at high altitude for a drone, characteristics that can be used in VAWT blade design. Airfoil Selection The airfoil shape contributes in the generation of a lift coefficient by creating suction on upper surface of the airfoil In this process, a drag is being generated which is not desirable for the maximum power output of the wind turbine. The increase in the power coefficient achieved up to 5% as compared to the use of the NACA0018 airfoil in a VAWT blade design. In the design of the double-element airfoil, the chord length of the slat airfoil (cs) was 35% of y/c

Wind tunnel experiment A wind tunnel testing is performed in this work to:

Findings

Conclusion