Three-dimensional flow visualization using laser-sheet scanning.

Conventional techniques of fixed laser sheet flow visualization can be extended to include three dimensional visualization by means of a scanning laser sheet. This system is implemented using a rotating mirror in conjunction with appropriate fixed optics. A space filling three dimensional data base is digitally obtained from the imaging and recording units, and is processed to yield a variety of three dimensional views of the flow field in addition to obtaining quantitative results regarding mixing levels and velocities. Laser sheet scanning was applied in a study of boundary layer turbulence in which active control was implemented. The flow visualization readily indicated the near wall instabilities present in turbulent spots and synthetic turbulent boundary layers. When control was attempted using an array of surface heating elements, the visualization technique graphically illustrated the attenuation of the near wall sublayer 'streaks' and resultant quiescent outer flow.