# What is the condition for Kutta Joukowski Theorem?

## What is the condition for Kutta Joukowski Theorem?

This is known as the Kutta condition. Kutta and Joukowski showed that for computing the pressure and lift of a thin airfoil for flow at large Reynolds number and small angle of attack, the flow can be assumed inviscid in the entire region outside the airfoil provided the Kutta condition is imposed.

What is the Kutta condition for a finite angle trailing edge?

If the angle made by the upper and lower surfaces of the aerofoil is finite, that is nonzero, then the trailing edge is a stagnation point at which the velocity is zero.

What is circulation theory?

The circulation theory of lift asserts that the difference in air speed over and under the wing results from a net “circulation” of air.

### Does circulation cause lift?

Circulation of a fluid around an object by itself will produce no lift. The classic example of this is the spinning cylinder with no other airflow.

Why is the Kutta condition important?

The Kutta condition allows an aerodynamicist to incorporate a significant effect of viscosity while neglecting viscous effects in the underlying conservation of momentum equation. It is important in the practical calculation of lift on a wing.

Is Kutta-Joukowski theorem related to lift?

Is Kutta-Joukowski theorem relate to lift? Explanation: The Kutta-Joukowski theorem relates the lift generated by an airfoil, to the speed of the airfoil. Through the fluid, the density of the fluid and the circulation.

## What is downwash in aircraft?

In aeronautics, downwash is the change in direction of air deflected by the aerodynamic action of an airfoil, wing or helicopter rotor blade in motion, as part of the process of producing lift.

What is Prandtl lifting line theory?

The Prandtl lifting-line theory is a mathematical model that predicts lift distribution over a three-dimensional wing based on its geometry. It is also known as the Lanchester–Prandtl wing theory. Lanchester in 1907, and by Ludwig Prandtl in 1918–1919 after working with Albert Betz and Max Munk.

What units is circulation in?

The dimensions of circulation are length squared, divided by time; L2⋅T−1, which is equivalent to velocity times length. In potential flow with a region of vorticity, all closed curves that enclose the vorticity have the same numerical value for circulation.

### What is aerodynamic circulation?

In physics, circulation is the line integral of a vector field around a closed curve. In fluid dynamics, the field is the fluid velocity field. Circulation was first used independently by Frederick Lanchester, Martin Kutta and Nikolay Zhukovsky. It is usually denoted Γ (Greek uppercase gamma).

Why does circulation generate lift?

Explanation based on flow deflection and Newton’s laws An airfoil generates lift by exerting a downward force on the air as it flows past. According to Newton’s third law, the air must exert an equal and opposite (upward) force on the airfoil, which is lift.

Can there be lift without circulation?

In case of a rotating cylinder or a cambered plate as shown in Figure 6, there will not be circulation without viscosity, and hence there will not be any lift. It is not diverting the air down but is only pushing it down to get the lift. Hence no work is done.

## Which is the correct description of the Kutta condition?

Kuethe and Schetzer state the Kutta condition as follows: A body with a sharp trailing edge which is moving through a fluid will create about itself a circulation of sufficient strength to hold the rear stagnation point at the trailing edge.

What causes an airfoil to have the Kutta condition?

The value of circulation of the flow around the airfoil must be that value which would cause the Kutta condition to exist. Comparison of zero-circulation flow pattern around an airfoil; and the flow pattern with circulation consistent with the Kutta condition, in which both the upper and lower flows leave the trailing edge smoothly.

How is lifting flow generated in a Kutta condition?

The answer lies in an analogy between flow around an airfoil and that around a cylinder in inviscid flow with circulation induced by a vortex (see Section 5.3.10 ). For the latter it can be shown that, when a point vortex is superimposed with a doublet on a uniform flow, a lifting flow is generated.

### Why do we need the Kutta condition in the momentum equation?

The reason we need the Kutta condition is purely mathematical. When the inviscid assumption is made, the order of the governing equations drops and we can no longer enforce two boundary conditions. If we look at the incompressible, viscous momentum equation: