Circulation Flashcards
Define lift per unit length due to circulation for any body in a 2D flow.
L = – rho * velocity * gamma, where gamma = circulation.
For a cylinder in a flow, describe the effect of rotating the cylinder.
The velocity on the side rotating with the flow increases, and the velocity on the side rotating against the flow decreases.
What flow feature is created by a finite span wing in a 3D flowfield?
Tip vortices.
What effect on the flowfield do tip vortices have on a wing that creates negative lift?
They induce an upwash component of velocity, increasing the effective onset velocity and thus, AoA of the wing.
How do tip vortices affect the forces on a wing?
They generate lift normal to the effective onset velocity.
Define lift per unit length due to circulation for any body in a 3D flow.
L_effective = – rho * velocity_effective * gamma, where gamma = circulation.
Resolve L_effective into its components.
The force Le can be resolved into lift normal to U, L, and induced drag parallel to U, Di.
What does the air at the TE do for ideal flow and on which surface?
Air on the pressure surface will reach the TE and turn around it, against the mean flow direction.
What does the air at the TE do for real flow and on which surface?
Air on the pressure surface reaches the TE, tries to turn around it. It can’t due to the p gradient, and it separates. Creates a starting vortex.
What does the starting vortex induce?
It must have a reaction, so circulation is created to balance it.
How does the starting vortex satisfy the Kutta Condition?
It aligns the separation point with the TE.
What effect does circulation have on an aerofoil?
It causes the velocity on the suction side to increase, and on the pressure side to decrease. This is what creates the p difference.
What wing property can be changed to decrease induced drag?
Increasing the span or aspect ratio, assuming constant lift.
