1. Fluctuations in passive scalar concentration convected by a helical flow in a conducting fluid
- Author
-
William B. Zimmerman
- Subjects
Fluid Flow and Transfer Processes ,Physics ,Convection ,Advection ,Turbulence ,Mechanical Engineering ,Scalar (mathematics) ,Computational Mechanics ,Mechanics ,Condensed Matter Physics ,Eddy diffusion ,Physics::Fluid Dynamics ,Mechanics of Materials ,Kurtosis ,Statistical physics ,Shear flow ,Wind tunnel - Abstract
Recent statistical analyses of field trials and wind tunnel experiments show a new feature of fluctuations of tracer concentration dispersing in turbulent shear flow. For an ensemble of releases, the scatter‐plot of the skewness S versus kurtosis K collapses to a quadratic curve lying above K=S2+1. Several explanations for this collapse have been put forth in the literature, including a model for cloud meander in instantaneous releases that does not treat the effects of turbulence on the internal structure of the cloud. In this paper, a model is proposed for the creation of internal striations within the cloud due to convection by the ABC‐velocity field that is a paradigm for three‐dimensional helical motions. The numerical simulations conducted here show that the collapse of the K‐S scatter plot obtains under this more complicated situation where the smaller than cloud size structure is created by chaotic advection. Further, these simulations complement a recent multiscale analysis for eddy diffusivity o...
- Published
- 1996