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Author: Gordon Richard Winkel
Publisher:
ISBN:
Category : Air
Languages : en
Pages : 0
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Experiments were conducted in a wind tunnel to investigate plume rise and plume growth in neutral atmospheric conditions. The modeling of fullscale plumes in the wind tunnel was studied. The use of plume momentum and the flux of buoyancy as scaling criteria proved successful in modeling plume behaviour. If this criteria is used the stack gas density can be varied between model and fullscale to achieve higher wind tunnel speeds with no effect on plume rise or dispersion. The study shows that careful attention must be given in modeling source conditions such as the stack efflux velocity profile due to its strong influence on plume rise and plume spread. The effects of both initial upward stack gas momentum and buoyant forces on plume rise were combined in a single expression that correlated with plume rise data in the wind tunnel. Plume rise was found to terminate at a downwind distance of 2200 L_ , where L is a buoyancy length scale for a plume, for the simulated atmospheric boundary layer shear flow tested. The effect of wind shear in the approach flow reduced plume rise by about 20% as compared to a uniform flow. The theory of Djurfors and Netterville (1978) closely predicted the reduction in plume rise due to wind shear. The Gaussian dispersion model for an elevated point source correctly characterized plume dispersion in the wind tunnel. Freestream velocity at stack height was chosen as a representative plume convection velocity for the Gaussian model. The plume spread due to buoyancy induced turbulence was measured in the wind tunnel and an expression was found to fit the data. Subsequent measurements showed that the interaction of buoyancy induced turbulence and atmospheric turbulence was nonlinear. An appropriate nonlinear correction was developed and successfully corrected for the initial growth due to buoyancy induced turbulence so that the spread due to atmospheric turbulence was recovered.
Author: Gordon Richard Winkel
Publisher:
ISBN:
Category : Air
Languages : en
Pages : 0
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Book Description
Experiments were conducted in a wind tunnel to investigate plume rise and plume growth in neutral atmospheric conditions. The modeling of fullscale plumes in the wind tunnel was studied. The use of plume momentum and the flux of buoyancy as scaling criteria proved successful in modeling plume behaviour. If this criteria is used the stack gas density can be varied between model and fullscale to achieve higher wind tunnel speeds with no effect on plume rise or dispersion. The study shows that careful attention must be given in modeling source conditions such as the stack efflux velocity profile due to its strong influence on plume rise and plume spread. The effects of both initial upward stack gas momentum and buoyant forces on plume rise were combined in a single expression that correlated with plume rise data in the wind tunnel. Plume rise was found to terminate at a downwind distance of 2200 L_ , where L is a buoyancy length scale for a plume, for the simulated atmospheric boundary layer shear flow tested. The effect of wind shear in the approach flow reduced plume rise by about 20% as compared to a uniform flow. The theory of Djurfors and Netterville (1978) closely predicted the reduction in plume rise due to wind shear. The Gaussian dispersion model for an elevated point source correctly characterized plume dispersion in the wind tunnel. Freestream velocity at stack height was chosen as a representative plume convection velocity for the Gaussian model. The plume spread due to buoyancy induced turbulence was measured in the wind tunnel and an expression was found to fit the data. Subsequent measurements showed that the interaction of buoyancy induced turbulence and atmospheric turbulence was nonlinear. An appropriate nonlinear correction was developed and successfully corrected for the initial growth due to buoyancy induced turbulence so that the spread due to atmospheric turbulence was recovered.
Author: Brian Henderson-Sellers
Publisher: Springer Science & Business Media
ISBN: 3642829767
Category : Technology & Engineering
Languages : en
Pages : 123
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Author: Owen Neiman
Publisher:
ISBN:
Category : Strip mining
Languages : en
Pages : 0
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A wind tunnel model was used to study stack plume dispersion at a surface-mining site. The interaction between plumes and the wake flows behind the stacks and large terrain obstacles (dikes) was investigated. Mean flow Reynolds number was about 25,000 times smaller in the wind tunnel than in the full scale atmospheric flow, affecting the dynamic similarity of the model. Stack wake flows were found to model downwash effects properly despite Reynolds number mismatch, as indicated by measured values of base pressure coefficient, -Cp^ - 0.86, for cylinders at model conditions, which were close to values from Roshko (1960) for cylinder flows at full scale Reynolds numbers. However, model dikes were found to greatly exaggerate the size of recirculation zones and influence of the dike wake flows on downwind velocity and turbulence levels. This problem was corrected using a deflector vane mounted on the model dike crests. A combined-rise formulation was developed which predicts both the momentum and buoyancy effect on plume rise. Momentum rise entrainment constants, predicted from a simple model from Wilson (unpublished) were found to yield accurate momentum rise predictions using the combined-rise formulation. Buoyancy rise entrainment constants $2 were found to vary realistically with changing flow conditions. The momentum flux ratio d).. was found to be well correlated with stack downwash effects, providing a means of prediction for this phenomenon. Dike wakes were found to increase measured ground level concentrations (GLC) from plumes, with a non-linear degree of severity with dike height. The Gaussian dispersion model was found to be adequate in predicting GLC. A correction model was proposed to account for dike effects on GLC through increased vertical plume spread o in the Gaussian model.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 37
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The operating ranges of meteorological wind tunnels for convective boundary layer (CBL) simulation are defined in this paper on a review of the theoretical and practical limitations of the flow phenomena and the facilities available. Wind-tunnel operating ranges are limited by the dimensions of the simulated circulations and of the tunnel itself, the tunnel flow speed and turbulence processes, and the characteristics of the measurement instrumentation. When it is desired to simulate both the convective boundary layer and the behavior of other flows imbedded within the boundary layer, such as power-plant plume rise and dispersion, then additional constraints exist on the fluid modeling process. The capabilities of meteorological wind tunnels can also be extended through the judicious use of boundary and side wall flow controls.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 32
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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There is a growing concern about the threat of a malicious release of harmful substances to the air in order to cause harm to the population. In order to help decision-makers assess the consequences of such an attack, accurate predictions of the transport and dispersion of airborne contaminants in cities are needed. The complex flows produced by buildings pose difficult challenges to dispersion modelers. Among features of concern are channeling of plumes down street channels, circular transport within street canyon vortex, upwind transport, and the retention of toxic materials trapped between buildings. Intermittent spiral vortices that develop on the downwind side of tall buildings and quickly transport material from the street surface to the top of the building are also commonplace. A number of groups have developed computational fluid dynamics that have been applied to neighborhood-scale problems and have explicitly resolved hundreds of buildings in their simulations. However, CFD models are computationally intensive and for some applications turn-around time is of the essence. For example, planning and assessment studies in which hundreds of cases must be analyzed or emergency response scenarios in which plume transport must be computed quickly. For many applications, where quick turn-around is needed (e.g., emergency response) or where many simulations must be run (e.g., vulnerability assessments), a fast response modeling system is required. Fast running models are not only needed for emergency response and post-event applications, but for scenarios in which many cases must be run or immediate feedback is needed. We have developed the QUIC (Quick Urban & Industrial Complex) dispersion modeling system to fill that need. It can relatively quickly compute the dispersion of airborne contaminants released near buildings. It is comprised of QUIC-URB, a model that computes a 3D mass consistent wind field for flows around buildings (Pardyjak and Brown, 2001), QUICPLUME, a model that describes dispersion near buildings (Williams et al., 2003), and a graphical user interface QUIC-GUI (Boswell et al., 2004). The QUIC dispersion code is currently being used for building scale to neighborhood scale transport and diffusion problems with domains on the order of several kilometers. Figure 1 illustrates the modeled dispersion for a release in downtown Salt Lake City. This paper describes the QUIC-PLUME randomwalk dispersion model formulation, the turbulence parameterization assumptions, and shows comparisons of model-computed concentration fields with measurements from a single-building wind-tunnel experiment. It is shown that the traditional three-term random walk model with a turbulence scheme based on gradients of the mean wind performs poorly for dispersion in the cavity of the single-building, and that model-experiment comparisons are improved significantly when additional drift terms are added and a non-local mixing scheme is implemented.
Author: D. J. Wilson
Publisher:
ISBN:
Category :
Languages : fr
Pages : 198
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Author: William H. Snyder
Publisher:
ISBN:
Category : Air
Languages : en
Pages : 204
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Author: R. L. Drake
Publisher:
ISBN:
Category : Air
Languages : en
Pages : 156
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Author: Edward R. Frederick
Publisher:
ISBN:
Category : Air
Languages : en
Pages : 352
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