Abstract

This wind tunnel study investigates the aerodynamic effects of Mini Gurney flaps (MGFs) and their combination with vortex generators (VGs) on the performance of airfoils and wind turbine rotor blades. VGs are installed on the suction side aiming at stall delay and increased maximum lift. MGFs are thin angle profiles that are attached at the trailing edge in order to increase lift at pre-stall operation. The implementation of both these passive flow control devices is accompanied by a certain drag penalty. The wind tunnel tests are conducted at the Hermann- Föttinger Institut of the Technische Universität Berlin. Lift is determined with a force balance and drag with a wake rake for static angles of attack from −5° to 17° at a constant Reynolds number of 1.5 million. The impact of different MGF heights including 0.25 %, 0.5 % and 1.0 % and an uniform VG height of 1.1 % of the chord length are tested on three airfoils that are characteristic for different sections of large rotor blades. Furthermore, the clean and the tripped baseline cases are considered. In the latter, leading edge transition is forced by means of Zig Zag (ZZ) turbulator tape. The preferred configurations are the smallest MGF on the NACA63(3)618 and the AH93W174 (mid to tip blade region) and the medium sized MGF combined with VGs on the DU97W300 (root to mid region). Next, the experimental lift and drag polar data is imported into the software QBlade in order to design a generic rotor blade. The blade performance is simulated with and without the add-ons based on two case studies. In the first case, the retrofit application on an existing blade mitigates the adverse effects of the ZZ tape. Stall is delayed and the aerodynamic efficiency is partly recovered leading to an improvement of the power curve. In the second case, the new design application allows for the design of a more slender blade while maintaining the power output. Moreover, the alternative blade appears to be more resistant against forced leading edge transition.

Highlights

  • 1.1 General outlineThe study is divided into the following sections

  • Different combinations of Mini Gurney flaps (MGFs) and vortex generators (VGs) are assessed by means of characteristic parameters, i.e. the lift performance, the stall behavior and the aerodynamic efficiency. 365 4.1 NACA63(3)618 4.1.1 Baseline Figure 9 shows the clean and the tripped polar curves

  • The present study investigates the use of MGFs and their combination with VGs for improved rotor blade performance of

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Summary

Introduction

1.1 General outlineThe study is divided into the following sections. The concepts, mechanisms and applications of Gurney flaps (GFs), ZZ tape and VGs are introduced.The literature review is focused on very small GF heights, so-called MGFs, and the combination of GFs with VGs.2. The study is divided into the following sections. The concepts, mechanisms and applications of Gurney flaps (GFs), ZZ tape and VGs are introduced. The literature review is focused on very small GF heights, so-called MGFs, and the combination of GFs with VGs. 2. The simulation software XFOIL (Drela, 1989) is used to determine the appropriate dimensions of each PFC device in relation to the local boundary layer thickness of the following airfoils: the NACA63(3)618, the AH93W174 and the DU97W300. The wind tunnel test section, the measurement methods and the data reduction process are specified including the force balance for the lift, and the wake rake for the drag measurements at a constant Reynolds number of Re = 1.5∙106

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