Turbulent boundary layer on a wall. A fog of tiny oil droplets is introduced into the laminar boundary layer on the test-section floor of a wind tunnel, and the layer then tripped to become turbulent. A vertical sheet of light shows the flow pattern 5.8 m downstream, where the Reynolds number based on momentum thickness is about 4000.
Reprinted (abstracted) with permission from Fig. 1, R.E. Falco: "Coherent motions in the outer region of turbulent boundary layers", Physics of Fliuids,Vol. 20,No.10, Part II, October 1977, page 5124. Copyright 1977 American Institute of Physics.