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boundary layer In fluidics, a narrow region next to a fixed boundary or surface where the fluid velocity rapidly changes from zero to some finite value.
boundary layer microscopic layer of fluid (liquid or gas) next to the surface of a body or object moving relative to it, important in considering the drag force upon the object. laminar boundary layer layer which is next to the surface of an object, not mixing with the flow further away from the surface, and so can be considered to be a discrete layer in a plane parallel to the main flow. turbulent boundary layer layer which is next to the surface of an object, but in this case mixing with the flow further away from it. An example of a boundary layer change is that due to a dimpled golf ball in flight: the dimples make the boundary layer turbulent, which reduces drag caused by the pressure being lower behind the ball, so less energy is lost to the flow.