The effect of Vortex Generators located on the pressure side of very thick wind turbine airfoils
Creators: name: Ramsay, Harry
name: Celik, Yunus
name: Wood, Ben
name: Dinwoodie, Iain
name: Masters, Ian
name: Harrold, Magnus
name: Manolesos, Marinos
Publisher: name: Zenodo
Year: 2023

description: Presentation form the 2023 Wind Energy Science Conference in Glasgow, organized by the European Academy of Wind Energy.Vortex generators (VGs) and wind turbines are not a new pairing, as they have long been used to increase performance [1]. However, the addition of VGs on the pressure side of the aerofoil is only seldom considered [2], [3]. This is surprising, given that large turbine profiles are at least 35% thick in the root region of the blades. Such profiles are prone to separation on the pressure side, especially when leading edge roughness is increased. The present study aims to investigate pressure side VGs, their effect on the flow and the resulting benefit to turbine performance and fatigue load reductions.
The investigation sits within scope of a larger wind turbine flow control project [4], where academic and industrial partners collaborate in order to further increase the benefit provided by VG's. Select wind tunnel and numerical results will be presented with a focus on the pressure side flow separation on a thick (35%) aerofoil. Triangular vane VGs were used to control the separated flow. The selected profile is typical of a wind turbine inner blade section and, due to the large thickness, is prone to flow separation on both sides.
The wind tunnel set-up setup allowed for simultaneous force and surface pressure measurements, as well as tuft flow visualization results. The mean pressure distribution over the aerofoil confirms that VGs indeed suppress separation on the pressure side. Tuft visualizations and Reynolds Averaged Navier Stokes (RANS) simulations show the existence of 3D separation of the Stall Cell type [5], while the force and pressure time series reveal a behaviour typical of unstable 3D separation [6], [7], with seemingly random switching between states and very low frequencies (St = 0.02) identified with the various states [8]. The presence of the VGs reduces both the unsteadiness and suppresses the instability in the flow for the tested angles of attack.
A number of data analysis techniques are being considered to further investigate the data, including data clustering algorithms such as the recently proposed combination of a Gaussian mixture model with Proper Orthogonal Decomposition [9] and the Density-Based Spatial Clustering of Applications with Noise (DBSCAN, [10]), demonstrated in Figure 4. The aim of these techniques is to identify the two or more potential states of the flow and in the final presentation the suitability of each technique will be discussed.
 
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