Flow analysis of airfoil having different cavities on its suction surface
07 Mar 2016-Progress in Computational Fluid Dynamics (Inderscience Publishers (IEL))-Vol. 16, Iss: 2, pp 67
TL;DR: In this paper, the fluid flow analysis of a symmetric airfoil having circular cavities on its suction surface at three different chordwise locations from leading to trailing edges is presented.
Abstract: The paper presents the fluid flow analysis of a symmetric airfoil having circular cavities on its suction surface at three different chordwise locations from leading to trailing edges. The leading edge cavity shapes were distorted using Bezier polynomial so that vortex trapping pattern in the cavities can be captured. Structured meshing scheme via a multi-block strategy was employed. Unsteady simulations were performed by a Reynolds averaged Navier-Stokes (RANS) solver. Lift, drag, pressure and skin friction coefficients were monitored at Reynolds number (Re) = 15 × 104 and 6 × 105 and different angles of attack. Cavity placed at the trailing edge produced better lift to drag ratio as compared to that of the other cavities. The distorted cavities performed badly in terms of lift and drag coefficients. The elliptical cavity shape showed better results at the angles of attack up to 10°.
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TL;DR: In this paper , a novel bent winglet structure for wind turbines is proposed to improve performance under both stationary and surge conditions, and the results show that the novel winglet exhibits superior performance, with a 14.5% improvement in performance compared to the conventional winglet under surge motion.
Abstract: The winglet has been widely deployed in the optimization of the blade design as it reduces the tip loss of the blade and increases the swept area of the rotor. However, previous studies have not adequately investigated the effect of platform motion on winglet performance in wind turbines. The objective of this study is to propose a novel bent winglet structure for wind turbines to improve performance under both stationary and surge conditions. To achieve this, the NREL Phase VI horizontal axis wind turbine (HAWT) is treated as a baseline. The numerical method employed is validated by comparing the simulated power and pressure coefficients of the HAWT with experimental data from the literature. The performance of the conventional winglet with the proposed novel winglet is compared in detail, taking into account the cant, twist, expansion direction, length, and winglet number of the conventional winglet. The results show that the novel bent winglet exhibits superior performance, with a 14.5% improvement in performance compared to the conventional winglet under surge motion. This study provides a feasible scenario for the optimization of onshore and offshore wind turbine designs.
TL;DR: In this article , the power performance of 2D H-type VAWT is enhanced by employing an optimum cavity on the suction side of the NACA 0018 blade airfoil.
Abstract: Vertical Axis Wind Turbine (VAWT) blades experience stall conditions at lower tip speed ratios during rotation, resulting in inefficient power performance. The power performance can be augmented by improving the blade's aerodynamic efficiency using active or/and passive flow control mechanisms. In this research, the power performance of 2-D H-type VAWT is enhanced by employing an optimum cavity on the suction side of the NACA 0018 blade airfoil. The optimum cavity shape was found using the Genetic Algorithm coupled with the Gaussian Process Regression (GPR) model at an airfoil static stall angle of attack in an isolated environment to reduce the computational cost of the optimization process. Two GPR models were employed to predict lift and drag coefficients, while the lift-to-drag ratio was used as an objective function in the optimization algorithm. 80 CFD runs were utilized for initial training and testing of the models, which reduced computational effort by 97% compared to a pure CFD-based optimization approach. The aerodynamic efficiency of the optimum cavity shape predicted by GPR models was also confirmed by CFD simulation, which showed only a 0.5% difference. For an airfoil with an optimum cavity, the aerodynamic efficiency was consistent at lower angles of attack. However, a significant rise of up to 31.8% was observed in the near stall region between 12° to 16° angle of attack in comparison to clean airfoil. The optimum cavity on baseline VAWT blades enhanced power performance by 63.8% at a TSR of 1.5. Moreover, at TSRs of 2, 2.5, 3, and 3.5, the enhancement in power performance was achieved by 34.4%, 22.2%, 16.1%, and 3.2%, respectively. This demonstrates the potential of employing an optimum cavity on the suction side for performance augmentation without applying the suction and a cost-effective solution by conducting optimization in an isolated environment.