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Unformatted text preview: regular laminar-turbulent interface, and vortex roll-up is visible. Further downstream (Fig. 6.3c) the puff becomes fully turbulent and very active, with helical motions visible. Far downstream (Fig. 6.3d), the puff is cone-shaped and less active, with
a fuzzy ill-defined interface, sometimes called the “relaminarization” region.
A complete description of the statistical aspects of turbulence is given in Ref. 1, while
theory and data on transition effects are given in Refs. 2 and 3. At this introductory level
we merely point out that the primary parameter affecting transition is the Reynolds number. If Re UL/ , where U is the average stream velocity and L is the “width,” or transverse thickness, of the shear layer, the following approximate ranges occur:
: highly viscous laminar “creeping” motion
laminar, strong Reynolds-number dependence
laminar, boundary-layer theory useful
transition to turbulence
turbulent, moderate Reynolds-number dependence
turbulent, slight Reynolds-number dependence These are representative ranges which vary somewhat with flow geometry, surface
roughness, and the level of fluctuations in the inlet stream. The great majority of our
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This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.
- Spring '08