Thick airfoils, Vortex Generators, Gurney Flaps and Flatback Solutions: How to get better performance out of the blade inner region?

The shape of the inboard part of wind turbine blades is a compromise among aerodynamic, structural, aeroelastic and transport requirements. The relative gravity of aerodynamic requirements decreases as the rotor diameter increases, which leads to challenging problems for aerodynamicists. How can we get the most out of the inboard part of the blade while securing sufficient structural integrity and with a reasonable chord?

Common answers to that question are the deployment of very thick (t/c>30%) airfoils with Vortex Generators (VGs) (1,2) or flatback airfoils with or without flow control devices (3–5). The present work investigates the subject via a comparative wind tunnel campaign. A typical inboard wind turbine airfoil (FFA-w3-360) with VGs and a flatback version (named FB20) of the same profile with and without flow control devices (VGs and Gurney Flaps (GFs) have been used for this study. The aim is to provide insight into the performance of the different profiles and devices under Wind Turbine relevant conditions (Re≈2M).

As a result of the collaborative framework between Swansea University and Vestas, all tests were performed at Swansea University Wind Tunnel and the models were provided by Vestas. The FFA-w3-360 model was fitted with pressure taps for time-averaged pressure measurements. The Flatback version of the model had a 20% thick trailing edge (TE) and was fitted with pressure taps, transient pressure sensors and microphones in the TE region. Both models were mounted on two force balances for redundant lift measurements. For validation purposes the FFA-w3-360 results with and without VGs are compared against wind tunnel measurements of the same profile from a different wind tunnel and the agreement is found to be good. Selected results from both profiles are given below.

As expected, FB20 provides higher lift and is less sensitive to tripping. Fixing transition leads to separation on the pressure side for FB20, while it adversely affects the flow on both sides of the FFA-w3-360.

The FFA-w3-360 profile was tested with VGs on the suction side at various chordwise locations, while FB20 was tested with VGs on both sides and with a GF. Out of the examined set ups, the thin TE profile with VGs at 30% was the best configuration for FFA-w3-360, while a GF with a height equal to 5% TE height was the best combination for FB20 and overall. In terms of Lift to Drag ratio the FFA-w3-360 with VGs at 30% chord was the overall best performing configuration.

The presentation will discuss the performance of the profiles and all devices in detail. Future analysis will include post processing of transient pressure, force and acoustic pressure measurements on FB20 to examine the effect of the various flow control devices on the flow.

This project was funded by Supergen ORE Hub Early Career Researcher Research Fund.