Drag coefficient

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drag coefficient

A dimensionless ratio of the component of force parallel to the direction of flow (drag) exerted on a body by a fluid to the kinetic energy of the fluid multiplied by a characteristic surface area of the body.

In symbols, the drag coefficient CD is
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where ρ is the fluid density, U the speed, and L a characteristic length of the body. Rayleigh's formula expresses the drag coefficient as proportional to a power of the Reynolds number (Re),
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For Couette flow, n = -1 and the constant is 2. In most aerodynamic experiments n lies between -1/4 and -1/2. The drag coefficient for the force exerted by the atmosphere on the earth is called the skin-friction coefficient.

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