Hydrodynamically rough surface

From Glossary of Meteorology

hydrodynamically rough surface

Any surface that by surface friction extracts momentum from the fluid flowing over it.

There are a number of measures of the roughness of a surface that relate to the degree of mixing in the fluid caused by this frictional overturning of the fluid.
See roughness length, friction velocity, zero-plane displacement;
compare aerodynamically rough surface, aerodynamically smooth surface.

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