Analysis of the Effect of Vortex Generator Spacing on Boundary Layer Flow Separation Control

Abstract

During the operation of wind turbines, flow separation appears at the blade roots, which reduces the aerodynamic efficiency of the wind turbine. In order to effectively apply vortex generators (VGs) to blade flow control, the effect of the VG spacing (λ) on flow control is studied via numerical calculations and wind tunnel experiments. First, the large eddy simulation (LES) method was used to calculate the flow separation in the boundary layer of a flat plate under an adverse pressure gradient. The large-scale coherent structure of the boundary layer separation and its evolution process in the turbulent flow field were analyzed, and the effect of different VG spacings on suppressing the boundary layer separation were compared based on the distance between vortex cores, the fluid kinetic energy in the boundary layer, and the pressure loss coefficient. Then, the DU93-W-210 airfoil was taken as the research object, and wind tunnel experiments were performed to study the effect of the VG spacing on the lift-drag characteristics of the airfoil. It was found that when the VG spacing was λ/H = 5 (H represents the VG's height), the distance between vortex cores and the vortex core radius were approximately equal, which was more beneficial for flow control. The fluid kinetic energy in the boundary layer was basically inversely proportional to the VG spacing. However, if the spacing was too small, the vortex was further away from the wall, which was not conducive to flow control. The wind tunnel experimental results demonstrated that the stall angle-of-attack (AoA) of the airfoil with the VGs increased by 10 • compared to that of the airfoil without VGs. When the VG spacing was λ/H = 5, the maximum lift coefficient of the airfoil with VGs increased by 48.77% compared to that of the airfoil without VGs, the drag coefficient decreased by 83.28%, and the lift-to-drag ratio increased by 821.86%.

Computational Methods for Modelling and Optimization of Flow Control Devices

“…Firstly, the clean airfoil curve shows its maximum peak before arriving to 12.45 • of AoA. However, when the DU97W300 has a VG on its suction side, the C L curve remains growing, as it is the principal effect of a VG implementation [28,29]. On the other hand, if the optimum GF length is applied for each AoA, higher C L values are reached for angles close to 0 • .…”

CFD-Based In-Depth Investigation of the Effects of the Shape and Layout of a Vortex Generator on the Aerodynamic Performance of a Multi-MW Wind Turbine

“…The distance between the VG pairs (λ) and the angle of attack (α) of the VG were specified as 6 • and 11 • for efficiency. The recommended λ/h investigated through a flat-plane CFD analysis study is 5 [32]. The VGs are installed on the suction surface and at the root of the blade to enhance the aerodynamic performance.…”

Quantitative Analysis of Drag Reduction Methods for Blunt Shaped Automobiles

“…There is also a third case when it is attached to the edge of the vehicle, these are known as flaps (see Figure 4c). The offset between two delta shaped winglets was examined in the work by Li et al [80]. They concluded that the maximum drag reduction was achieved at 5 offset distance/VG height ratio.…”