The DNS data were analyzed that a zero-pressure-gradient, flat-plate boundary layer with a passively heated wall that spatially develops from a Blasius laminar state, through by-pass transition, to a developed turbulent state. Statistical properties (mean velocity, Reynolds stresses, kinetic energy production and dissipation rates, enstrophy and its components) of the turbulence in transition, from individual turbulent spots and where the spots merge, were compared to those for the developed boundary layer turbulence downstream. When the distributions in the transitional regions are conditionally averaged so as to exclude locations and times when the flow is not turbulent, they closely resemble the distributions in the developed turbulent state at the higher Reynolds number, especially in the buffer layer. An octant analysis based on the combinations of signs of the velocity and temperature fluctuations, u, v and q, showed that the momentum and heat fluxes are predominantly of the mean gradient type in both the transitional and developed regions. The fluxes appear to be closely associated with vortices that transport momentum and heat toward and away from the wall in both regions of the flow. The results suggest that there may be little fundamental difference between the non-linear processes involved in the formation of turbulent spots that appear in transition and those that sustain the turbulence when it is developed. They also support the view that the transport processes and the vortical structures that drive them in developed and transitional boundary layer turbulence are, in many dynamically important respects, similar.

 

James Wallace is the Professor in the Department of Mechanical Engineering at the University of Maryland at College Park. He received B.S. and M.S. degrees in 1962 and 1964 from the Georgia Institute of Technology and D. Phil. in Engineering Science from Oxford University in 1969. He was on the research staff of the Max-Planck-Institut für Strömungsforschung (fluid flow research,) in Göttingen, Germany from 1969 until he joined the faculty of the University of Maryland in 1975. In addition to his research and teaching, he has held several academic administrative positions at Maryland. From 1985 - 87 he was the Assistant Provost of the Division of Mathematics, Physical Science and Engineering. From 1993 - 1998 he served as Associate Chairman for Graduate Studies in the Department of Mechanical Engineering. He currently is the Board Chair of the Burgers Program for Fluid Dynamics. He also helped found and directed two Science, Technology and Society programs at Maryland and he directed the Gemstone Program for undergraduate honors team research since 2001.

 

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