You are here:
EXPERIMENTS ON BUOYANT PLUME DISPERSION IN A LABORATORY CONVENTION TANK
Citation:
Weil, J. C., W H. Snyder, R E. Lawson Jr., AND M. S. Shipman. EXPERIMENTS ON BUOYANT PLUME DISPERSION IN A LABORATORY CONVENTION TANK. BOUNDARY-LAYER METEOROLOGY 102(3):367-414, (2002).
Impact/Purpose:
This task objective is the development and improvement of state-of-the-science meteorology models and contributing process parameterizations for use in advanced air quality simulation model systems such as the Community Multi-scale Air Quality (CMAQ) modeling system and for other modeling studies and situations involving transport and dispersion of pollutants. Components of this work include: (a) improved meteorological and transport modeling, (b) improved meteorological modeling physics, (c) physical modeling of flows- building wakes, complex terrain, urban canyons, (d) modeling of transport and dispersion of specialized situations and (e) develop AERMOD (AMS/EPA Regulatory MODel).
Description:
Buoyant plume dispersion in the convective boundary layer (CBL) is investigated experimentally in a laboratory convection tank. The focus is on highly-buoyant plumes that loft near the CBL capping inversion and resist downward mixing. Highly- buoyant plumes are those with dimensionless buoyancy fluxes F* >/~ 0.1, , where F* = Fb/(Uw2/*zi), Fb is the source buoyancy flux, U is the mean wind speed, w* is the convective velocity scale, and zi is the CBL depth. The aim is to obtain statistically-reliable mean (C) and root-mean-square (rms, sigma c) concentration fields and plume characteristics as a function of F* and the dimensionless distance
X = w*x/( U zi), where x is the distance downstream of the source.
The experiments show the following. I) For 3 /- 0.1 , the crosswind-integrated concentration (CWIC) fields exhibit distinctly uniform profiles below zi with a CWIC maximum aloft, in contrast to the nonuniform profiles obtained earlier by Willis and Deardorff (1987). 2) The lateral dispersion (sigma y) variation with X is consistent with Taylor's (1921) theory for F* 1.5 , but sigma c/C exhibits significant increases: a) at the surface and close to the source (X /- 2, with the mixed-layer group collapsing to a single distribution independent of z.
These are the first experiments to obtain all components of the lateral and vertical dispersion parameters (rms meander, relative dispersion, total dispersion) for continuous releases in a convective tank. They also are the first tank experiments to demonstrate agreement with field observations of: 1) the scaled ground-level concentration along the plume centerline, and 2) the lateral dispersion sigma y/zi of buoyant plumes.