What types of boundary layers can be found on an aero foil?
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A
Laminar layer at the leading wing areas, turbulent boundary layer at the trailing areas.
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B
Turbulent boundary layer along the complete upper surface with separated airflow.
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C
Turbulent layer at the leading wing areas, laminar boundary layer at the trailing areas.
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D
Laminar boundary layer along the complete upper surface with non-separated airflow.
Refer to figure.
The boundary layer is the layer of fluid (in our case this fluid is the atmosphere) in the immediate surface of a bounding surface (the airfoil) where the effects of viscosity are significant. There are two types of boundary layer; the laminar and the turbulent boundary layer.
In the laminar boundary layer, the flow moves parallel to the surface over which it flows. In the laminar boundary layer, the air flows very smoothly. The velocity increases with distance from the airfoil and there is no movement of air perpendicular to the surface of the airfoil. Laminar flow creates less friction drag than turbulent flow but is less stable.
At a distance from the leading edge of the airfoil, the air transitions from a laminar flow to a turbulent flow. This air does not flow smoothly, it contains swirls. There is flow in parallel and perpendicular direction. This air creates more drag than the laminar air flow but breaks down less easily and is therefore more stable.
Therefore, the laminar boundary layer on the aero foil is located between the stagnation point and the turbulent transition point.
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Austro Control