Vortex Trapping by Different Cavities on an Airfoil
TL;DR: In this paper, the authors presented the flow over an airfoil with different cavity shapes placed on the suction surface of a symmetric airframe, and the cavity with both sharp edges showed better results in terms of lift and drag as compared to other shapes of the cavity.
Abstract: 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.
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22 Jun 2020
TL;DR: In this article, the authors 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.
Abstract: 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
7 citations
TL;DR: 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.
Abstract: 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.
6 citations
5 citations
01 Jun 2021
3 citations
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.
2 citations
Cites background from "Vortex Trapping by Different Caviti..."
...Besides, several efforts have been done on the aerodynamic characteristic of the airfoil with cavity [25-28]....
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References
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TL;DR: In this paper, the two-dimensional characteristics of airfoil NACA 0018 have been measured for Reynolds numbers between 0.15x106 and 1.0x106 to establish the lift, drag and moment curves that serve as input to performance calculations of vertical axis wind turbines.
Abstract: The two-dimensional characteristics of airfoil NACA 0018 have been measured for Reynolds numbers between 0.15x106 and 1.0x106 to establish the lift, drag and moment curves that serve as input to performance calculations of vertical axis wind turbines. At the lower surface laminar separation occurs at low to medium angles of attack, which is of significant influence on the characteristics and the radiated noise. For the situation with a lower surface laminar separation bubble, span wise wake rake traverse measurements showed an irregular three-dimensional pattern. Noise reduction could be achieved with zigzag tape at the 70% to 80% lower surface chord station. Significant post-stall hysteresis loops occurred showing a high loss in lift.
145 citations
"Vortex Trapping by Different Caviti..." refers result in this paper
...4a shows that the present result which is RANS simulation for the airfoil matches well with the experimental results [8, 24]....
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TL;DR: In this article, the effects of rotation on blade boundary layers are investigated by solving the 3D integral boundary layer equations with assumed velocity profiles, and detailed flow fields are simulated on the conditions of 2D stationary and 3D rotation by CFD code.
81 citations
TL;DR: In this article, a two-dimensional direct numerical simulation of the flow over a NACA0018 airfoil with a cavity is presented, where the authors validate the results by means of flow visualizations carried out in a water channel.
Abstract: Two-dimensional direct numerical simulation of the flow over a NACA0018 airfoil with a cavity is presented. The
low Reynolds number simulations are validated by means of flow visualizations carried out in a water channel. From
the simulations, it follows that there are two main regimes of flow inside the cavity. Depending on the angle of attack,
the first or the second shear-layer mode (Rossiter tone) is present. The global effect of the cavity on the flow around
the airfoil is the generation of vortices that reduce flow separation downstream of the cavity. At high positive angles of
attack, the flow separates in front of the cavity, and the separated flow interacts with the cavity, causing the
generation of smaller-scale structures and a narrower wake compared with the case when no cavity is present. At
certain angles of attack, the numerical results suggest the possibility of a higher lift-to-drag ratio for the airfoil with
cavity compared with the airfoil without cavity.
38 citations
"Vortex Trapping by Different Caviti..." refers background or result in this paper
...From the literature [1] it has been found that the oscillations of the shear layer above the cavity generate small vortices which suppress the separation of boundary layer downstream of the cavity....
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...In reality the separated flow is three dimensional and turbulent [1]....
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...Cavity_LE_NACA 0018, Re = 2 × 10(4) [1]...
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...4b it is observed that the results for the airfoil with cavity are following the trend of the DNS results [1]....
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...[1] shows that the airfoil with a cavity on the suction surface showed better performance in terms of lift coefficient (Cl) and drag coefficient (Cd)....
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TL;DR: In this paper, a flow due to a vortex trapped in a cavity is considered and the total circulation is constant and the Kutta condition is satisfied at the separation point when the vortex is on the equilibrium position S. The suction/blowing intensity of the sinks/sources located on the flow boundary is determined by using a classical variational technique.
Abstract: The flow due to a vortex trapped in a cavity is considered. The total circulation is constant and such that the Kutta condition is satisfied at the separation point when the vortex is on the equilibrium position S. If the vortex is slightly displaced from S it moves on closed trajectories. By using a classical variational technique, the suction/blowing intensity of the sinks/sources located on the flow boundary is determined so that the vortex is driven back to S. Examples of precomputed control and feed-back control in several flow configurations, including unstable equilibria and in the presence of random perturbations, are given.
32 citations
"Vortex Trapping by Different Caviti..." refers background in this paper
...The vortex in the cavity can be controlled by suction/blowing employed at the wall [15]....
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TL;DR: In this article, it was shown that there exist bodies such that in two-dimensional steady inviscid incompressible flow the pressure gradient is favorable over the entire surface of the body, and the lift is non-zero, if the body is immersed in a uniform stream and there are also two trapped point vortices.
Abstract: It is shown that there exist bodies such that in two-dimensional steady inviscid incompressible flow the pressure gradient is favourable over the entire surface of the body, and the lift is non-zero, if the body is immersed in a uniform stream and there are also two trapped point vortices.
27 citations
"Vortex Trapping by Different Caviti..." refers background in this paper
...Several articles report the separation phenomenon in terms of boundary layer pressure distribution using inviscid flow theory but the separation is a predominantly viscous phenomenon [6]....
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...Both the boundary layer theory and observations show that a boundary layer never separates when the pressure does not increase in the direction of the flow [6] and negative pressure gradient is called favorable pressure gradient....
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