Abstract
This study focuses on the effect of the upward deflection of trailing edge flap (TEF) on the strength and trajectory of dynamic stall vortex (DSV) around a pitching airfoil by means of numerical simulations based on unsteady Reynolds-averaged Navier-Stokes (URANS). The effect of the upward deflection of the TEF on the unsteady aerodynamic forces due to DSV is analyzed. The numerical simulation method for large mesh deformation is constructed. Radial basis function- (RBF-) based mesh deformation algorithm, as well as Laplacian and optimization-based mesh smoothing algorithm, is adopted to ensure the mesh quality in flow field simulations. The results reveal that the upward deflection of the TEF can reduce the peaks of drag and pitching moment coefficients. Although the maximum lift coefficient of the airfoil is slightly reduced, its maximum drag and pitching moment coefficients are significantly reduced by up to 34.8% and 31.8%, respectively. The vorticity transport behavior in a planar control region during the DSV formation and detachment is analyzed. It is found that the TEF can change the development process of the DSV. The upward deflection of the TEF reduces the vorticity flux from the leading edge shear layer, which causes the circulation of the DSV and the translational velocity of the vortex center to decline. The peaks of the unsteady aerodynamic forces on the airfoil induced by the DSV are reduced. The upward deflection of the TEF plays the role of alleviating the pitching moment load. The longer TEF can result in a better control effect. The bigger the upward deflection angle of the TEF, the better its control effect.
Highlights
Dynamic stall refers to a kind of flow phenomenon in which the stall is delayed beyond the static stall angle of attack when an airfoil is experiencing unsteady motion [1]
From an examination of the aerodynamic loads, it is apparent that these high loads were a consequence of the dynamic stall that occurred on the outboard portion of the retreating blade, and this dynamic stall behavior was intimately related to the control system and blade torsional flexibility
Visbal et al proposed a high-frequency control concept for dynamic stall mitigation targeting the natural instabilities of laminar separation bubble (LSB) to delay the formation of dynamic stall vortex (DSV) [11–13], which is worthy of further research
Summary
Dynamic stall refers to a kind of flow phenomenon in which the stall is delayed beyond the static stall angle of attack when an airfoil is experiencing unsteady motion [1]. The wind tunnel test and numerical simulation results showed a dramatic decrease in the drag and pitching moment associated with severe dynamic stall when the VDLE concept is applied to the Boeing VR-12 airfoil. Visbal et al proposed a high-frequency control concept for dynamic stall mitigation targeting the natural instabilities of laminar separation bubble (LSB) to delay the formation of DSV [11–13], which is worthy of further research. Feszty et al [15] analyzed the effect of the TEF on the mitigation of large negative pitching moment and negative aerodynamic damping caused by DSV. It is recommended to dynamically pitch the TEF out of phase with the airfoil pitching to reduce the peaks of the lift and pitching moment coefficients and reduce the negative aerodynamic damping that can lead to stall flutter. The influence of the upward deflection of the TEF on the development process of the DSV, as well as the vorticity transport behavior, is analyzed
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