Active control of the tip vortex: an experimental investigation on the performance characteristics of a model turbine

E Anik,O Uzol,Y Ostovan,B Mercan,A Abdulrahim

doi:10.1088/1742-6596/524/1/012098

Abstract

This study is part of an on-going experimental research campaign that focuses on the active control of the tip leakage/vortex characteristics of a model horizontal axis wind turbine rotor using tip injection. This paper presents both baseline (no-injection) data as well as data with tip injection, concentrating on the effects of tip injection on power and thrust variations with the Tip Speed Ratio (TSR). The experiments are conducted by placing a specially designed 3-bladed model wind turbine rotor at the exit of a 1.7 m diameter open-jet wind tunnel. The rotor blades are non-linearly twisted and tapered with NREL S826 airfoil profile all along the span. The nacelle, hub and the blades are specifically designed to allow pressurized air to pass through and get injected from the blade tips while the rotor is rotating. Baseline results show that the general trends are as expected for a small wind turbine and the maximum power coefficient is reached at around TSR=4.5. Results with injection show that the tip injection has significant effect on the power and thrust coefficients in comparison to the baseline data, especially at TSR values higher than the max CP TSR value. Both coefficients seem to be significantly increased due to tip injection and the max CP TSR value also gets shifted to a slightly higher TSR value. Tip injection seems to have no significant effect for TSR values less than 3.5.

Highlights

The primary source of the tip vortex is the pressure difference between the upper and lower surfaces of a blade and the related flow leakage at the blade tips
This study is part of an on-going experimental research campaign that focuses on the active control of the tip leakage/vortex characteristics of a model horizontal axis wind turbine rotor using tip injection
Results show that the injection has significant effect on the power and thrust coefficients in comparison to the baseline data, especially at higher Tip Speed Ratio (TSR) values

Summary

Introduction

The primary source of the tip vortex is the pressure difference between the upper and lower surfaces of a blade and the related flow leakage at the blade tips. When the leakage flow meets with the main stream, concentrated vortical structures get generated. These vortex structures can cause a variety of performance losses and noise problems for horizontal axis wind turbines. These vortices can cause structural and performance problems due to vortex-turbine interactions in successively arranged wind turbines in wind farms. Active Flow Control (AFC) is generally proposed to control the boundary layer characteristics such as transition or separation on a wind turbine. AFC using tip injection in wind turbine blades can be applied for controlling the tip leakage/vortex characteristics. Some previous implementations are fixed wings (e.g. Margaris and Gursul (2004) [16], Mercan et al (2010) [17], Ostovan (2011) [18], Bettle (2004) [19]) as well as helicopter (e.g. Duraisamy and Baeder (2004) [20], Vasilescu (2004) [21], Liu et al (2000) [22], Han and Leishan (2004) [23]) and turbomachinery blades (e.g. Mercan et al (2012) [24], Rao (2005) [25], Niu and Zang (2011) [26])

Methods

Results

Conclusion