This says the Joukowski transformation is 1-to-1 in any region that doesn’t contain both z and 1/z. This is the case for the interior or exterior of. The Joukowski transformation is an analytic function of a complex variable that maps a circle in the plane to an airfoil shape in the plane. A simple way of modelling the cross section of an airfoil or aerofoil is to transform a circle in the Argand diagram using the Joukowski mapping.

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The Russian scientist Nikolai Egorovich Joukowsky studied the function. He showed that the image of a circle passing through and containing the point is mapped onto a curve shaped like the cross section of an airplane wing.

We call this curve the Joukowski airfoil.

Joukowski Airfoil: Geometry – Wolfram Demonstrations Project

If the streamlines for a flow around the circle are known, then their images under the mapping will be streamlines for a flow around the Joukowski airfoil, as shown in Figure Forming the quotient of joukowxki two quantities results in the relationship. Which is verified by the calculation.


However, the composition functions in Equation must be considered in order to visualize the geometry involved. These three compositions are shown in Figure The restriction on the angleand henceis necessary in order for the arc to have a low profile.

The arc lies in the center of the Joukowski airfoil and is shown in Figure Now we are transformatuon to visualize the flow around the Joukowski airfoil. We start with the fluid flow around a circle see Figure For illustrative purposes, we let and use the substitution.

Points at which the flow has zero velocity are called stagnation points.

Ifthen there is one stagnation point on the unit circle. Ifthen the stagnation point lies outside the unit circle. We are mostly interested in the case with two stagnation points.

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Whenthe two transfirmation points arewhich is the flow discussed in Example The cases are shown in Figure We are now ready to combine the preceding ideas.


The advantage of this latter airfoil is that the sides of its tailing edge form an angle of radians, orwhich is more realistic than the angle of of the traditional Joukowski airfoil.

The following Mathematica subroutine will form the functions that are needed to graph a Joukowski airfoil. For a fixed value dxincreasing the parameter dy will bend the airfoil.

For a fixed value dyincreasing the parameter dx will fatten out the airfoil. Increasing both parameters dx and dy will bend and fatten out the airfoil.

Refer to Figure Exercises for Section Joukowski Transformation and Airfoils. Return to the Complex Analysis Project. This material is coordinated with our book Complex Analysis for Mathematics and Engineering.

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