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, the effect of hinge position (H) has been numerically investigated to find the appropriate position for improving the aerodynamic performance of the NACA 0012 flapped airfoil.
Abstract: In the present study, the effect of hinge position (H) has been numerically investigated to find the appropriate position for improving the aerodynamic performance of the NACA 0012 flapped airfoil. In addition, perpendicular and tangential suctions have been applied to control the flow separation and enhance the aerodynamic performance over the NACA 0012 flapped airfoil at each different hinge positions. The simulations were carried out at a Reynolds number of 5 × 105 (Ma = 0.021) based on two-dimensional incompressible unsteady Reynolds-averaged Navier–Stokes calculations to determine the adequate hinge position. The turbulence was modeled using the shear stress transport k–ω turbulence model. The effect of perpendicular suction (θjet = − 90°) and tangential suction (θjet = − 30°) was computationally studied over NACA 0012 flapped airfoil for five different hinge positions (H = 0.7c, 0.75c, 0.8c, 0.85c and 0.9c) and a flap deflection (δf) of 15°. Based on the results, the hinge position significantly affects the aerodynamic performance of the airfoil. The lift coefficient increased clearly as the hinge position moved to the trailing edge of the airfoil. Using perpendicular suction caused to increase the lift coefficient and decrease the drag coefficient. Consequently, the maximum value of the lift-to-drag ratio (CL/CD) for perpendicular and tangential suctions was achieved about 35.8% and 25.1% higher than that of the case without suction at an angle of attack of 12° and H = 0.9c. Also, the effect of perpendicular suction was more considerable compared to the tangential suction. This caused a reduction in the size of the recirculation zone from 0.5 to 0.09 of the airfoil chord length and also transferred it from 1.13 to 1.18 of the airfoil chord length.
5 citations
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TL;DR: A cavity on a Risø_B1_18 airfoil, which is used as a wind turbine airfoils, was optimized at an off-design angle of attack by incorporating a genetic algorithm into a RANS flow solver and showed that the optimized cavity traps a vortex, which postpones the stall.
Abstract: Airfoils are mostly inefficient in their off-design conditions. In order to improve the aerodynamic performance of airfoils in these conditions, using an optimized cavity on airfoils as a passive method can be useful. In this study, a cavity on a Riso_B1_18 airfoil, which is used as a wind turbine airfoil, was optimized at an off-design angle of attack by incorporating a genetic algorithm into a RANS flow solver. For the cavity optimization, the geometry and downstream suction surface were defined by 16 parameters, and the lift-to-drag ratio was considered as the cost function at 14° angle of attack. The numerical solution showed that the optimized cavity traps a vortex, which postpones the stall. Due to the uncertainty of CFD especially at off-design conditions, it was necessary to evaluate the performance of the optimized cavity in a wide range of angles of attack. This study used the particle image velocimetry (PIV) measurement method to evaluate the improved flow structures over the optimized cavity.
Two models of airfoils with and without the cavity were made of aluminum and installed inside the test section of an open-jet wind tunnel with an air speed of 30 m/s and a cross section of 30 × 30 cm2. The air flow on the suction side of the airfoils was measured at 7°–15° angles of attack by PIV. A comparison between the measured flow fields over the two airfoils showed that the optimized cavity postpones the stall angle by 3°. Furthermore, the cavity increases the momentum behind the airfoil at the angles of attack greater than 9°.
After this angle, a further increase in the angle of attack increases the difference between the momentums behind the airfoils with and without cavity. The Riso_B1_18 airfoil with the optimized cavity can be used as a wind turbine airfoil at high angles of attack to increase the stall angle and decrease the instability and fluctuation at off-design conditions.
4 citations
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TL;DR: In this article , the authors incorporated a spherical dimple on the NACA (National Advisory Committee for Aeronautics) 4415 leading edge as a passive flow control device and compared the aerodynamic performances with the plain NACA 4415 airfoil.
Abstract: The flow separation occurred at an early angle of attack (AOA) in airfoil directs the researchers to focus on the methods of flow controlling. The present study incorporated a spherical dimple on the NACA (National Advisory Committee for Aeronautics) 4415 leading edge as a passive flow control device and compared the aerodynamic performances with the plain NACA 4415 airfoil. The dimple diameter (d) was varied from 1% to 6% of the chord length (0.01C-0.06C) to generate four numbers of the modified airfoil. A chord-based Reynolds number (Re) of 2 × 105 was selected for the present study. Shear-Stress Transport (SST) k-ω turbulence model with SIMPLE (semi-implicit method for pressure linked equations) scheme was chosen to solve the present problem computationally in ANSYS FLUENT 14.0. The results showed that the modification helped in delaying stall by 6° at the expense of 0.8% maximum lift coefficient with a dimple diameter of 0.01C. The modified airfoils experienced a primary low-velocity circular zone near the trailing edge and a secondary circulation zone at the dimple edges. In contrast, only one larger circulation zone was present near the plain airfoil trailing edge. The smallest dimple (d = 0.01C) showed a maximum lift enhancement ratio and lift to drag enhancement ratio of 14.8% and 7.86%, respectively.
3 citations
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TL;DR: In this paper , the effect of circular cavity on aerodynamic performance of the H-Darrieus rotor is investigated using a subsonic wind tunnel test facility to check which side cavity on the airfoil (inner or outer side) is beneficial in terms of the rotor's static and dynamic performances.
Abstract: This present investigation is carried out to improve the performance of H-Darrieus wind turbine in the built environment, where it mostly experiences low wind speed. Here the effect of circular cavity on aerodynamic performance of the rotor is investigated using a subsonic wind tunnel test facility to check which side cavity on the airfoil (inner or outer side) is beneficial in terms of the rotor’s static and dynamic performances. For this, S1046 and NACA 0021 airfoil blades are considered at various low wind speeds of 5, 6 and 7 m/s for different rotor aspect ratios. A Computational Fluid Dynamics (CFD) study is also simultaneously conducted to realize the intrinsic flow physics of the cavity airfoil blade profile. Results show that inner surface cavity on both the blades improves their self-starting ability but only at 5 m/s wind speed, which is not so when wind speed is 7 m/s at which NACA 0021 blade without cavity performs better. Again, NACA 0021 blade without cavity exhibits the highest performance of all the considered blade shapes, for which the highest power coefficient of 0.15 is achieved at a tip speed ratio of 1.25 and wind speed 6 m/s. At wind speed 7 m/s, the NACA 0021 blade rotor having outside cavity has a lower maximum power coefficient but wider operating range than that of NACA 0021 blade without cavity. CFD results show that H-Darrieus rotor having NACA 0021 blades at 30° azimuthal angle with circular cavity at 1/4th chord distance from its leading edge located at its inner surface, can generate higher lift force. However, circular cavity will be useful for starting performance of H-Darrieus rotor, which is not so for its dynamic performance, although operating range is improved.
2 citations
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TL;DR: In this article, a Computational Fluid Dynamics (CFD) investigation is carried out for analyzing the simultaneous effect of suction and cavity for controlling flow separation on NACA 0012 airfoil.
Abstract: In the present research, a Computational Fluid Dynamics (CFD) investigation is carried out for analyzing the simultaneous effect of suction and cavity for controlling flow separation on NACA 0012 airfoil. Hence, a perpendicular suction jet (jet = -90°) is employed with Rjet equal to 0.15 at Ljet = 0.1c. Simultaneously, a cavity is used at 90% of chord length (0.9c) with 20 mm width and 10 mm depth. The fluid flow is assumed to be 2D turbulent, and incompressible. The results demonstrate that lift coefficient has raised by 30% and drag coefficient has decreased by 40% at α = 14° by using simultaneous suction and cavity. The flow control method improves lift to drag ratio and stall angle has increased from 14° to 22°. Consequently, the flow separation has been delayed, the recirculation zone has gone downstream and completely eliminated by utilizing simultaneous suction and cavity as an effective flow control method.
1 citations
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