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The boundary layer of a wing is:

  • A

    a turbulent flow around the wing.

  • B

    created by the normal shock wave at transonic speeds.

  • C

    caused by suction on the upper wing surface.

  • D

    a layer on the wing in which the stream velocity is lower than the free stream velocity.

Refer to figure.
BOUNDARY LAYER

When a solid is placed into a flow, there will be a layer, where the velocity is smaller than in the undisturbed stream, reducing to 0 at the surface of the body.

Boundary Layer is defined as a region where the velocity of the flow reaches a certain percentage (i.e. 90% or 99%) of the undisturbed stream velocity from zero. Inside the boundary layer, the viscosity of the fluid alters the flow, while outside of this layer viscosity can be neglected.

The boundary layer will exist in two forms, either laminar or turbulent. In general, the flow at the front will be laminar and become turbulent some distance back, known as the transition point.

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