Image: Types of flow analysis in fluid mechanics

Description: Example of the different types of flow analysis encountered in fluid mechanics, for a flow past a partly-stalled, flapped airfoil.   Far away from the airfoil, frictional effects within the fluid can be neglected. It is then customary to calculate pressure, speed and (in the case of compressible flow) density distribution using potential flow theory.   In the close vicinity of the airfoil, viscous friction is the dominating effect determining fluid behavior. Is is then customary to calculate fluid trajectory and predict transition and separation points using boundary layer theory. Pressure across (but not along) the boundary layer is uniform to a good approximation.   In separated and turbulent wake areas, neither potential flow nor boundary layer theory assumptions hold. This unsteady area is home to complex, unpredictable flow patterns and is usually studied using wind tunnel observations. Note: boundary layer thickness is greatly exaggerated for illustration purposes, its border is not a streamline; all flow patterns in this figure are merely for illustrative purposes.
Author: Olivier Cleynen
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License: CC-BY-SA-3.0
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