A laboratory study of diffussion in stably stratified flow

Chaudhry, Fazal Hussain; Meroney, Robert N.

doi:10.1016/0004-6981(73)90103-0

Cited by 10 publications

(2 citation statements)

References 11 publications

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“…This means that the growth of the plume in the vertical direction is attenuated by stable stratification. The results are in qualitative agreement with previous measurements (Chaudhry & Meroney 1973;Britter et al 1983). Figure 10 shows the vertical distributions of the vertical mass flux normalized by the product ofŪ and C 0 under the three stratified conditions.…”

Section: Resultssupporting

confidence: 90%

The difference in turbulent diffusion between active and passive scalars in stable thermal stratification

Nagata

Komori

2001

J. Fluid Mech.

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The difference in turbulent diffusion between active scalar (heat) and passive scalar (mass) in a stable thermally stratified flow is investigated both experimentally and numerically. The experiments are conducted in an unsheared thermally stratified water flow downstream of a turbulence-generating grid. Passive mass is released into the stable thermally stratified flow from a point source located 60 mm downstream from the grid. Instantaneous streamwise and vertical velocities, the temperature of the active scalar and the concentration of the passive scalar are simultaneously measured using a combined technique with a two-component laser-Doppler velocimeter (LDV), a resistance thermometer and a laser-induced fluorescence (LIF) method. From the measurements, turbulent heat and mass fluxes and eddy diffusivities for both active heat and passive mass are estimated. To investigate the Prandtl or Schmidt number effects on the difference in turbulent diffusion between active heat and passive mass, a three-dimensional direct numerical simulation (DNS) based on a finite difference method is applied to stable thermally stratified flows of both water and air behind the turbulence grid. The Schmidt number of passive mass in the DNS is set to the same value as the Prandtl number of active heat.The results show that stable stratification causes a large difference in eddy diffusivities between active heat and passive mass. The numerical predictions by the DNS are in qualitative agreement with the measurements despite the assumption of the same molecular diffusivity for active heat and passive mass. The difference suggests that the assumption of identical eddy diffusivity for active heat and passive mass, used in conventional turbulence models, gives significant errors in estimating heat and mass transfer in a plume under stably stratified conditions.

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Section: Resultssupporting

confidence: 90%

The difference in turbulent diffusion between active and passive scalars in stable thermal stratification

Nagata

Komori

2001

J. Fluid Mech.

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“…For instance, early experiments (e.g. Arya 1968; Chaudhry and Meroney 1973;Ohya et al 1997) focused on the flow characteristics and diffusion in the SBL with different Richardson numbers. Recently, Ohya et al (2008) investigated intermittent bursting in an SBL with a low-level jet.…”

Section: Introductionmentioning

confidence: 99%

Effects of Thermal Stability and Incoming Boundary-Layer Flow Characteristics on Wind-Turbine Wakes: A Wind-Tunnel Study

Chamorro

Porté‐Agel

2010

Boundary-Layer Meteorol

239

168

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Wind-tunnel experiments were carried out to study turbulence statistics in the wake of a model wind turbine placed in a boundary-layer flow under both neutral and stably stratified conditions. High-resolution velocity and temperature measurements, obtained using a customized triple wire (cross-wire and cold wire) anemometer, were used to characterize the mean velocity, turbulence intensity, turbulent fluxes, and spectra at different locations in the wake. The effect of the wake on the turbulence statistics is found to extend as far as 20 rotor diameters downwind of the turbine. The velocity deficit has a nearly axisymmetric shape, which can be approximated by a Gaussian distribution and a power-law decay with distance. This decay in the near-wake region is found to be faster in the stable case. Turbulence intensity distribution is clearly non-axisymmetric due to the non-uniform distribution of the incoming velocity in the boundary layer. In the neutral case, the maximum turbulence intensity is located above the hub height, around the rotor tip location and at a distance of about 4-5.5 rotor diameters, which are common separations between wind turbines in wind farms. The enhancement of turbulence intensity is associated with strong shear and turbulent kinetic energy production in that region. In the stable case, the stronger shear in the incoming flow leads to a slightly stronger and larger region of enhanced turbulence intensity, which extends between 3 and 6 rotor diameters downwind of the turbine location. Power spectra of the streamwise and vertical velocities show a strong signature of the turbine blade tip vortices at the top tip height up to a distance of about 1-2 rotor diameters. This spectral signature is stronger in the vertical velocity component. At longer downwind distances, tip vortices are not evident and the von Kármán formulation agrees well with the measured velocity spectra.

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Estimation of lagrangian time scales from laboratory measurements of lateral dispersion

Meroney

1984

Atmospheric Environment (1967)

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A laboratory study of diffussion in stably stratified flow

Cited by 10 publications

References 11 publications

The difference in turbulent diffusion between active and passive scalars in stable thermal stratification

The difference in turbulent diffusion between active and passive scalars in stable thermal stratification

Effects of Thermal Stability and Incoming Boundary-Layer Flow Characteristics on Wind-Turbine Wakes: A Wind-Tunnel Study

Estimation of lagrangian time scales from laboratory measurements of lateral dispersion

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