Formation of a Starting Vortex for Symmetric Aerofoils (NACA 0015)

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In summary, the study investigates the formation of a starting vortex around symmetric aerofoils, specifically the NACA 0015 profile. It explores the mechanisms of vortex formation during the initial stages of lift generation when the aerofoil is subjected to an angle of attack. The research employs theoretical models and computational fluid dynamics to analyze the flow characteristics and vortex dynamics, revealing insights into the influence of viscosity and initial conditions on the vortex structure. The findings contribute to a better understanding of aerodynamic performance and potential improvements in aerofoil design.
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JackFyre
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TL;DR Summary
Question regarding lift force on a symmetric aerofoil
Greetings!

An aerofoil experiences life because the velocity of flow at the top surface of the airfoil is higher, causing a pressure difference. This higher velocity is attained as a consequence of the conservation of angular momentum due to the formation of a starting vortex at the trailing edge of an aerofoil. However, I have read that symmetric aerofoils (like the NACA 0015) do not generate lift at a 0 angle of attack. Why is this so? Is it because there is no starting vortex at zero angle of attack for symmetric foils? And if so, why? What determines the formation of the strating vortex and subsequent lift genaration?
Starting vortex - MIT.gif
 
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Symmetric airfoils facing airflow at zero AOA induce an exactly equal pressure distribution profile (amount of disturbance to the molecules of air) on each side.

That pressure profile is a reflection of the ways in which the velocity of the molecules in contact with each surface varies from the stagnation point (at the leading edge) all the way to the trailing edge of the wing.

The vertical stabilizer of any airplane is a good example of this.
Please, see:
https://en.wikipedia.org/wiki/Vertical_stabilizer

Pressure-distribution-for-a-symmetric-airfoil-at-0-and-10-angle-of-attack.png


ztMCG.png


 
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  • #3
Uh, fit flaps / ailerons and/or analogous devices ?
Given you need such to control the wannabe lawn-dart in absence of thrust vectoring etc...
Or have I misunderstood the question ??
 
  • #4
Nik_2213 said:
Uh, fit flaps / ailerons and/or analogous devices ?
Given you need such to control the wannabe lawn-dart in absence of thrust vectoring etc...
Or have I misunderstood the question ??
I was just curious about the formation of the starting vortex in symmetric airfoils, and how it may explain why symmetric foils show 0 lift at 0 AoA. Thanks!
 
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FAQ: Formation of a Starting Vortex for Symmetric Aerofoils (NACA 0015)

What is a starting vortex and why is it important in the study of aerofoils?

A starting vortex is a rotational region of fluid that forms at the trailing edge of an aerofoil when it begins to move through a fluid. It is important because it is associated with the generation of lift. The starting vortex is shed into the wake, and according to the Kutta-Joukowski theorem, this process leads to the establishment of circulation around the aerofoil, which in turn generates lift.

How does the NACA 0015 aerofoil specifically contribute to the formation of a starting vortex?

The NACA 0015 is a symmetric aerofoil, which means it has no camber and its upper and lower surfaces are mirror images. When this aerofoil begins to move, the flow separates symmetrically at the trailing edge, leading to the formation of a starting vortex. The symmetry of the NACA 0015 ensures that the vortex formation is uniform, making it an ideal subject for studying the fundamental principles of starting vortex dynamics.

What experimental methods are commonly used to study the formation of starting vortices in aerofoils?

Experimental methods to study starting vortices typically include flow visualization techniques such as smoke or dye injection, Particle Image Velocimetry (PIV), and high-speed photography. Wind tunnel testing is also commonly used, where the aerofoil is placed in a controlled flow environment to observe and measure the vortex formation and its characteristics.

What role does the angle of attack play in the formation of the starting vortex for the NACA 0015 aerofoil?

The angle of attack significantly influences the formation and strength of the starting vortex. For the NACA 0015 aerofoil, as the angle of attack increases, the separation point of the flow moves forward along the chord of the aerofoil, leading to a stronger and more pronounced starting vortex. At zero angle of attack, the vortex formation is symmetric, but as the angle increases, asymmetry in the vortex formation can occur, affecting the lift and drag characteristics.

How do computational fluid dynamics (CFD) simulations contribute to understanding the starting vortex formation in NACA 0015 aerofoils?

CFD simulations provide detailed insights into the flow patterns and vortex dynamics that are challenging to capture experimentally. By solving the Navier-Stokes equations numerically, CFD can predict the behavior of the starting vortex, including its formation, strength, and evolution over time. For the NACA 0015 aerofoil, CFD simulations can help visualize the symmetric vortex formation and study the effects of different flow conditions, angles of attack, and Reynolds numbers on the starting vortex.

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