A TURBULENCE MODEL FOR VARYING DENSITY FLOW IN GENERAL CURVILINEAR COORDINATES

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NUMERICAL MODELLING OF FLOW FIELD IN A TIDAL RIVER AND THE NEAR FIELD OF INTAKE FOR A NUCLEAR POWER PLANT

This Paper concerns with the numerical modelling of flow field in a tidal river and in the vicinity ofintake of a nuclear power plant. The hybrid method of fractional steps presented in [1] was adopted in thismodelling. In order to simulate the local flow field nearby the water intake meticulously, the technique ofthe match of the coarse and fine grids was used. The numerical results are in good agreement with thein-situ measurements of the main current. The detailed data of local flow field nearby the intake providesthe assessment of the sediment transport characteristics in the vicinity of intake of the nuclear powerplant.     

EFFECT OF NON-SPHERICAL PARTICLES ON THE FLUID TURBULENCE IN A PARTICULATE PIPE FLOW

In the non-spherical particulate turbulent flows,a set of new fluid fluctuating velocity equations with the nonspherical particle source term were derived, then a new method,which treats the slowly varying functions and rapidly varying functions separately, was proposed to solve the equations, and finally the turbulent intensity and the Reynolds stress of the fluid were obtained by calculating the fluctuating velocity statistically. The equations and method were used to a particulate turbulent pipe flow. The results show that the turbulent intensity and the Reynolds stress are decreased almost inverse proportionally to the fluctuating velocity ratio of particle to fluid. Nonspherical particles have a greater suppressing effect on the turbulence than the spherical particles. The particles with short relaxation time reduce the turbulence intensity of fluid, while the particles with long relaxation time increase the turbulence intensity of fluid. For fixed particle and fluid, the small particles suppress the turbulence and the large particles increase the turbulence.     

NUMERICAL SIMULATION FOR THE STEPPED SPILLWAY OVERFLOW WITH TURBULENCE MODEL

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｓｔｅｐｐｅｄｓｐｉｌｌｗａｙｈａｄｂｅｅｎｕｓｅｄａｔｔｈｅｂｅｇｉｎｎｉｎｇｏｆｔｗｅｎｔｙｃｅｎｔｕｒｙ[1 ] .Ｉｎ 1 971 ,Ｅｓｓｅｒｙｅｔａｌ.[2 ] ｃｏｎｄｕｃｔｅｄａｍｏｄｅｌｔｅｓｔｆｏｒｔｈｅｄｅｓｉｇｎｏｆ     

THEORY AND NUMERICAL ANALYSIS OF THE INTERACTION BETWEEN TURBULENCE AND SUSPENDED SEDIMENTs

The coupled hydrodynamical-ecological model for Regional and Shelf Seas Coherens was modified through introducing sediment model in order to simulate suspended sediment transport and account for the interaction between turbulence and sediment. To discuss the effects of sediment on vertical eddy viscosity and diffusion coefficients, the damping function of sediment on turbulence was introduced into one equation k-ε turbulence closure model. Moreover, it is assumed that local equilibrium among turbulence production, dissipation and buoyancy destruction exist near the bottom. The local equilibrium assumption is introduced into the one equation k-ε model and the specific formulation of local equilihrium for one equation k-ε was derived. The tidal current was calculated for Youngkwang Bay near the west coast of Korea. Meanwhile, the suspended sediment was also simulated with the local equilibrium assumption and damping function of sediment on turbulence. It is found that the damping function of sediment reduces vertical eddy viscosity and diffusion coefficients. The local equilibrium assumption changes obviously bottom layer turhulence intensity and sediment concentration.     

ON THE FINITE DIFFERENCE METHODS FOR TWO DIMENSIONAL TURBULENCE BOUNDARY LAYER

In this paper,the author first establishes the general finite difference formula for the governing equations ofthe turbulent average velocities in a steady two dimensional incompressible fluid boundary layer-inner layer.Next,three key parameters of the difference scheme are determined respectively by several simple flow models with knownanalytical solutions.Finally a special five points difference system is given and its application value is showed by anumerical example for the vertical velocity distribution in an Ekman's layer.     

A PREDICTING MODEL OF THE LIMITING FLUX FOR THE CHARGED SOLUTE IN ULTRAFILTRATION PROCESS

In the process of ultrafiltration , the occurrence of the limiting flux is elucidated with the formation of a cake(gel) layer on the membrane surface. Before cake formation, the pressure drop on the concentration polarization layer, as well as the permeate flux, increases with the applied pressure. The pressure drop on the concentration polarization layer, however, will no longer change with the applied pressure after the formation of the cake layer. The limiting flux will be obtained if the hydrodynamic conditions in the filtration channel are not affected by the cake layer. A mathematics model for predicting the limiting flux for the charged solute in ultrafiltration is developed. In this model, a repulsive electric force is taken into account in addition to convection and diffusion when the solute is carrying the same charge as the membrane material. A procedure to correlate the model with experimental ultrafiltration data is also present. The results show that a model in this paper is developed on a more realistic perception of the ultrafiltration system and the predicting data agrees well with experimental data.     

A HYBRID MODEL FOR THE MERGING OF JETS IN A COFLOWING AMBIENT FLUID

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＧｅｎｅｒａｌｌｙｔｈｅｄｉｓｐｅｒｓｉｏｎｏｆｊｅｔｓａｎｄｐｌｕｍｅｓｉｎａｍｏｖｉｎｇｅｎｖｉｒｏｎｍｅｎｔｃａｎｂｅｒｅｌａｔｅｄｔｏｔｈｅｄｉｓｐｏｓ ａｌｏｆｕｒｂａｎａｎｄｉｎｄｕｓｔｒｉａｌｗａｓｔｅｗａｔｅｒ     

THE APPLICATION AND DEVELOPMENT OF TURBULENCE MODELS IN BUOYANT RECIRCULATING FLOWS

In this paper, a modified κ-ε turbulence model, a simplified algebraic stress model and a developed two-fluidmodel have been presented based on numerical modeling of turbulent buoyant recirculating flows. The calculatedresults by these models are in good agreement with experiments. However, the last model is much better forsimulating gravity-stratified flows.     

THEORY AND NUMERICAL ANALYSIS OF THE INTERACTION BETWEEN TURBULENCE AND SUSPENDED SEDIMENT

1.INTRODUCTIONThe damping function of sedi ment on turbu-lence becomes an obvious phenomenon near thebottom where sedi ment induced density stratifica-tion is usually significant.The vertical sedi mentdiffusion coefficient has inti mate relationto turbu-lence.So the damping function has i mportanteffect on sedi ment transport.Many researchershave paid much attention to the interaction be-tween turbulence and suspended sedi ment since theability to accurately predict the sedi ment transpor…     

SECOND-ORDER MOMENT TWO-PHASE TURBULENCE MODEL ACCOUNTING FOR TURBULENCE MODULATION IN SWIRLING SUDDEN-EXPANSION CHAMBER

A semi-empirical turbulence enhancement model accounting for the particle-wake effect was incorporated into the second-order moment two-phase turbulence model and employed to simulate gas-particle flows in a swirling sudden-expansion chamber. The simulated results for two-phases mean velocities and fluctuation velocities coincide well with the experiment ones, which demonstrates that this model, in comparison with the turbulence model not accounting for the wake effect, leads to higher calculating accuracy.     

THE TURBULENCE CHARACTERISITICS OF OPEN CHANNEL FLOW

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A SECOND-ORDER MOMENT TURBULENCE MODEL FOR POWER LAW FLUID WITH PARTICLES

The USM-θ model of power law fluid for dense two-phase turbulent flow was developed, which combines the unified second-order moment model for two-phase turbulence with the particle kinetic theory for the inter-particle collision. This model was used to simulate the turbulent flow of power law fluid single-phase in pipe. It is shown that the USM ? θ model has better prediction result than the k f ? ε f?kp?εp?θ model. The USM ? θ model was then used to simulate the dense two-phase turbulent up flow of power law fluid with particles. With the increase of the flow exponent, the velocities of power law fluid and particles increase near the pipe centre. Comparison between the two-phase flow of power law fluid-particle and of liquid-particle indicates that the axial fluctuation velocity of fluid phase and particle phase in liquid-particle two-phase flow is smaller than that in the power law fluid two-phase flow, but the two-phase velocities of power law fluid-particle and liquid-particle are close to each other.     

THE CHARACTERISTICS OF TURBULENCE AND DISPERSION IN SURFACE LAYER OF COASTAL REGION

By analyzing turbulence data measured at two sites in coastal regions of Hangzhoubay,it is discovered that:(1)The turbulent intensity I_k is inversely proportional to the windspeed at lower speed.While at higher wind speed,it keeps basically to be constant.(2)Underthe unstable conditions in the vicinity of sea shore,the dimensionless standard deviations of windspeed σ_k/U(?) are constants basically,while in the inland,they can be described by the expressionssimilar to Panofsky(1977)models but with different constants.Under the stable conditions,they are constants when Z/L<0.2 and proportional to 1/3 power of Z/L for larger Z/L.(3)Near the coast,the variation of U(?)/U with Z/L follows Businger(1971)model U(?)/U =k/(?)(Z/L)very well not only under stable but also under unstable condition.Inland,it is coincidentvery well merely under the condition-1.0≤Z/L≤0.3.Out this range,the deviation islarge.(4)The dispersion parameters can be described in the form recommended by Draxler(1976)but with different constants.Under the unstable condition,they can also be expressed asBriggs(1985)model with different constants.     

STRUCTURAL EQUATION MODELLING: A NOVEL STATISTICAL FRAMEWORK FOR EXPLORING THE SPATIAL DISTRIBUTION OF BENTHIC MACROINVERTEBRATES IN RIVERINE ECOSYSTEMS

Benthic macroinvertebrates have been used widely as bioindicators to assess the condition of riverine ecosystems. However, understanding and modelling the spatial distribution of benthic macroinvertebrates within these ecosystems remain significant challenges for research and management. Statistical analyses of multivariate data sets offer opportunities to explore the ecological systems controlling the distribution of biota. This article reports a novel statistical analysis of a national‐scale data set from England and Wales using the structural equation modelling (SEM) framework. Relationships between water quality, physical habitat structure and indices reflecting benthic macroinvertebrate community structure were analysed using SEM. On the basis of data from 219 monitoring sites, structural equation models were built. These models explained 87% of the spatial variation in the average score per taxon index and 76% of the spatial variation in the Lotic Invertebrate Index for Flow Evaluation. Significant direct and indirect effects on these indices were exerted by water quality variables, particularly the concentrations of dissolved oxygen, biochemical oxygen demand and orthophosphate. Independent of water quality conditions, both biotic indices were directly affected by variables describing the structure and the degradation of physical habitat. The strengths of the SEM framework include (i) direct evaluation of a priori models against observed data, thereby supporting confirmatory analysis of theoretical models of ecological systems; (ii) specification of latent variables representing unmeasured constructs; and (iii) simultaneous assessment of multiple direct and indirect paths between variables within a model. These strengths define a framework with the potential to be applied widely in the development and testing of hypotheses regarding the processes operating within riverine ecosystems. Copyright © 2012 John Wiley & Sons, Ltd.     

THE NUMERICAL SIMULATION OF TWO-DIMENSIONAL OPEN CHANNEL TURBULENCE

A numerical simulation on 2-D open channel turbulence using the two-equationturbulent model(k-e model) is made.The diseretization equations of depth-averaged 2-D differ-ential equation are obtained by the control-volume formulation.Some examples including theflows in straight open channel,symmetry sudden expansion and one-side sudden expansion arecalculated by using the SIMPLE algorithm.The distributions of the flow velocity u,the kineticturbulent energy k,and the turbulent viscosity μ,etc.are obtained.The numerical calculationsindicate a good agreement with experimental data and other turbulent models calulations.