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611.
1 IntroductionMiniaturizationofanalyticalsystemhasbeenpaidmuchattentiontointherecentyearsforitsobviousadvantages:fastanalysis,portability,reducedconsumptionofreagentsandimprovingper formance .Suchdeviceisso calledaslaboratory on a chip[1 ],whichistheinte… 相似文献
612.
613.
A new method of introducing the free-surface effects in the calculation of turbulent open-channel flows using the amplitude of the free-surface fluctuation is proposed along with a modeling method of the equation for the free-surface fluctuation. It can be incorporated in two-equation models like k-or k-type models by introducing the damping factor to represent the interaction of the eddies with the fluctuating free-surface. Test calculations for fully developed flows and those over backward-facing step indicate good agreement with direct numerical simulation results as well as experimental results. 相似文献
614.
A One-Equation Turbulence Model for Geophysical Applications: Comparison with Data and the k−ε Model
A one-equation turbulence model is presented, in which the turbulent kinetic energy k is calculated with a transport equation whereas the turbulent length scale l is calculated with an algebraic expression. The value of l depends on the local stratification and reduces to the classical |z| scaling for unstratified flows near a wall, where |z| is the distance to the wall. The length scale decreases during stable stratification, and increases for unstable stratification compared to the neutral case. In the limit of strong stable stratification, the so-called buoyancy length scale proportional to k
1/2
N
–1 is obtained, where N is the buoyancy frequency. The length scale formulation introduces a single model parameter which is calibrated against experimental data. The model is verified extensively against laboratory measurements and oceanic data, and comparisons are made with the two-equation k- model. It is shown that the performance of the proposed k model is almost identical to that of the k- model. In addition, the stability functions of Launder are revisited and adjusted to obtain better agreement with recent data. 相似文献
615.
Gerhard H. Jirka 《Environmental Fluid Mechanics》2006,6(1):43-100
An integral model for the plane buoyant jet dynamics resulting from the interaction of multiple buoyant jet effluxes spaced
along a diffuser line is considered as an extension of the round jet formulation that was proposed in Part I. The receiving
fluid is given by an unbounded ambient environment with uniform density or stable density stratification and under stagnant
or steady sheared current conditions. Applications for this situation are primarily for submerged multiport diffusers for
discharges of liquid effluents into ambient water bodies, but also for multiple cooling tower plumes and building air-conditioning.
The CorJet model formulation describes the conservation of mass, momentum, buoyancy and scalar quantities in the turbulent
jet flow in the plane jet geometry. It employs an entrainment closure approach that distinguishes between the separate contributions
of transverse shear and of internal instability mechanisms, and contains a quadratic law turbulent pressure force mechanism.
But the model formulation also includes several significant three-dimensional effects that distinguish actual diffuser installations
in the water environment. These relate to local merging processes from the individual multiple jets, to overall finite length
effects affecting the plume geometry, and to bottom proximity effects given by a “leakage factor” that measures the combined
affect of port height and spacing in allowing the ambient flow to pass through the diffuser line in order to provide sufficient
entrainment flow for the mixing downstream from the diffuser. The model is validated in several stages: First, comparison
with experimental data for the asymptotic, self-similar stages of plane buoyant jet flows, i.e. the plane pure jet, the pure
plume, the pure wake, the advected line puff, and the advected line thermal, support the choice of the turbulent closure coefficients
contained in the entrainment formulation. Second, comparison with data for many types of non-equilibrium flows with a plane
geometry support the proposed functional form of the entrainment relationship, and also the role of the pressure force in
the jet deflection dynamics. Third, the observed behavior of the merging process from different types of multiport diffuser
discharges in both stagnant and flowing ambient conditions and with stratification appears well predicted with the CorJet
formulation. Fourth, a number of spatial limits of applicability, relating to terminal layer formation in stratification or
transition to passive diffusion in a turbulent ambient shear flow, have been proposed. In sum, the CorJet integral model appears
to provide a mechanistically sound, accurate and reliable representation of complex buoyant jet mixing processes, provided
the condition of an unbounded receiving fluid is satisfied. 相似文献
616.
In large-eddy simulations of atmospheric boundary layer turbulence, the lumped coefficient in the eddy-diffusion subgrid-scale
(SGS) model is known to depend on scale for the case of inert scalars. This scale dependence is predominant near the surface.
In this paper, a scale-dependent dynamic SGS model for the turbulent transport of reacting scalars is implemented in large-eddy
simulations of a neutral boundary layer. Since the model coefficient is computed dynamically from the dynamics of the resolved
scales, the simulations are free from any parameter tuning. A set of chemical cases representative of various turbulent reacting
flow regimes is examined. The reactants are involved in a first-order reaction and are injected in the atmospheric boundary
layer with a constant and uniform surface flux. Emphasis is placed on studying the combined effects of resolution and chemical
regime on the performance of the SGS model. Simulations with the scale-dependent dynamic model yield the expected trends of
the coefficients as function of resolution, position in the flow and chemical regime, leading to resolution-independent turbulent
reactant fluxes. 相似文献
617.
In order to evaluate the performance of different methods for estimation of the vertical eddy diffusivity in thermally stratified
lakes, two field studies were conducted in Lake Biwa, Japan and Lake Kinneret, Israel. Lake Biwa experienced three typhoons
during the campaign while Lake Kinneret experienced high winds in the afternoons. Microstructure profiles were collected by
a portable flux profiler (PFP) during calm and disturbed periods. Then, the vertical eddy diffusivity was estimated by three
indirect methods. The estimated vertical eddy diffusivities varied more than one order of magnitude, from 4.7× 10−7 to 7.7× 10−6 m2 s−1. The comparison of results with previous buoyancy flux measurements and scaling arguments showed that the Dillon–Park’s method
is not appropriate and Osborn–Cox method performs better than Osborn method in the studied case. Furthermore, the low value
of vertical eddy diffusivity within the thermocline suggests that within the thermocline of these lakes, diffusive vertical
transport can be neglected. 相似文献
618.
阐述炼油厂污水处理场污泥的组成、性质及污泥脱水的实际情况,在原工艺处理流程的基础上采取增加污泥储存罐、污泥调理系统、污泥输送系统等设施,并进行一系列的技术改造,使得污泥脱水系统能够正常平稳运行,减少污泥对环境的污染.取得了一定的经济效益和社会效益。 相似文献
619.
620.
流动注射催化光度分析法的研究进展 总被引:3,自引:0,他引:3
综述了近年来流动注射催化光度分析法的研究进展,包括环境水样中金属离子、阴离子、有机物等污染物的测定,展望了流动注射催化光度分析法未来的研究方向和发展前景。 相似文献