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.

Effects of the hinge position and suction on flow separation and aerodynamic performance of the NACA 0012 airfoil

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.

Evaluation of aerodynamic performance enhancement of Risø_B1 airfoil with an optimized cavity by PIV measurement

Engineered surface textures can manipulate boundary layers affecting fluid drag We study periodic, infinitely long spanwise grooves on a laminar boundary layer over a plate for 1000 $R\phantom{\rule{0}{0ex}}{e}_{L}$ 25000 Below a certain width-to-depth aspect ratio (AR), a primary vortex inside each groove causes the freestream to ``slip over'', reducing skin friction Increasing AR poses a tradeoff in drag reduction due to pressure drag from groove vertical walls Overall, transverse grooves for laminar flow can reduce total drag up to 10% compared to a flat plate, despite increasing the wetted surface area

Study of drag reduction using periodic spanwise grooves on incompressible viscous laminar flows

In this paper the flow characteristics and velocity fields over the vertical axis wind turbines DU 06 W 200 airfoil developed by Delft University of Technology and some other innovative designs are examined by computational fluid dynamics (CFD) simulation and particle image velocimetry (PIV) measurements. In these case studies a modification of the plain airfoil upper and/or lower surfaces was applied with the assistance of different techniques. CFD was conducted using the turbulent model of RANS k- ω SST. The PIV experiments were performed using a wind tunnel test and smoke flow visualization. Different practical cases, namely riblet under surface, riblet above surface, cavity front, cavity back, double cavity, single riblet, and spoiler, were designed and examined. Moreover, two hybrid blade airfoils designed and inspired by combining the DU 06 W 200 and NACA 63215 developed by National Advisory Committee for Aeronautics (NACA) were also tested. The results show that the new design hybrid blade airfoil can significantly modify the flow pattern over the airfoil and improve aerodynamic performance. The new design hybrid blade airfoil could deliver improved efficiency for industrial applications, specifically for the design and development of vertical axis wind turbines. 

The effects of surface modification on aerodynamic characteristics of airfoil DU 06 W 200 at low Reynolds numbers

https://ascelibrary.org/doi/pdf/10.1061/%28ASCE%290893-1321%281995%298%3A4%28197%29

New Airfoil-Design Concept with Improved Aerodynamic Characteristics

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°.

Flow analysis of airfoil having different cavities on its suction surface

The paper presents the flow over an airfoil with different cavity shapes placed on the suction surface of a symmetric airfoil. Unsteady simulations of flow over the airfoil with and without cavities were performed by Reynolds averaged Navier-Stokes (RANS) solver. Lift and drag were checked and the separation point identified at different Reynolds numbers and different angles of attack. The airfoil with cavity produced more drag and less lift as compared to the airfoil without cavity. The cavity with both sharp edges showed better results in terms of lift and drag as compared to other shapes of the cavity.

Aswin Vuddagiri

Papers

Flow analysis of airfoil having different cavities on its suction surface

Vortex Trapping by Different Cavities on an Airfoil