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A numerical model for air concentration distribution in self-aerated open channel flows

Journal of Hydrodynamics 2015年第3期27卷 394-402页

作者：卫望汝邓军张法星田忠 State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University

The self-aeration in open channel flows, called white waters, is a phenomenon seen in spillways and steep chutes. The air distribution in the flow is always an important and fundamental issue. The present study develops a numerical model to predict the air concentration distribution in self-aerated open channel flows, by taking the air-water flow as consisting of a low flow region and an upper flow region. On the interface between the two regions, the air concentration is 0.5. In the low flow region where air concentration is lower than 0.5, air bubbles diffuse in the water flow by turbulent transport fluctuations, and in the upper region where air concentration is higher than 0.5, water droplets and free surface roughness diffuse in the air. The air concentration distributions obtained from the diffusion model are in good agreement with measured data both in the uniform equilibrium region and in the self-aerated developing region. It is demonstrated that the numerical model provides a reasonable description of the self-aeration region in open channel flows.

关键词： self-aeration air concentration open channel flows turbulence diffusion numerical model

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Experimental Study of the diffusion of a Confined Wall Jet through a Perforated Plate: Influence of the Porosity and the Geometry

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Open Journal of Fluid Dynamics 2022年第1期12卷 96-126页

作者： Moussa Diop Denis Flick Graciela Alvarez Jean Moureh Refrigerating Process Engineering Unit INRAE Antony Antony France UMR SayFood AgroParisTech INRAE Université Paris Saclay Massy France

This paper investigated lateral diffusion of a confined two-dimensional wall jet (air inlet height: 5 cm) through a perforated plate. We considered two plates with porosities of and . The plates were positioned at distances of 10 cm and 20 cm below the jet inlet. The experiments were realized using 2D Laser Doppler Anemometer (LDA). Different profiles of mean and fluctuating velocities are presented. The presence of a perforated plate strongly modified the airflow pattern compared to an empty enclosure. The velocities above and below the plate depend on several parameters, including the porosity and the plate’s position relative to the inlet slot and the longitudinal position. The difference between the flow velocity above and below the plates could not be related using a universal formula that depends on these parameters. We also investigated the influence of a porous media of a height of 20 cm (a stack of spheres having a diameter of 3.75 cm) located below the perforated plate. The results highlight that the porous medium strengthens the effects of the perforated plate on the flow.

关键词： Porous Medium Perforated Plate Wall Jet Air Ventilation Aeraulic turbulence diffusion

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Experimental and Numerical Investigation of the diffusion of a Confined Wall Jet through a Perforated Plate

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Open Journal of Fluid Dynamics 2022年第2期12卷 168-212页

作者： Moussa Diop Denis Flick Graciela Alvarez Jean Moureh Refrigerating Process Engineering Unit INRAE Antony Antony France Université Paris Saclay INRAE AgroParisTech UMR SayFood Massy France

When performing numerical modeling of fluid flows where a clear medium is adjacent to a porous medium, a degree of difficulty related to the condition at the interface between the two media, where slip velocity exists, is encountered. A similar situation can be found when a jet flow interacts with a perforated plate. The numerical modeling of a perforated plate by meshing in detail each hole is most often impossible in a practical case (many holes with different shapes). Therefore, perforated plates are often modeled as porous zones with a simplified hypothesis based on pressure losses related to the normal flow through the plate. Nevertheless, previous investigations of flow over permeable walls highlight the impossibility of deducing a universal analytical law governing the slip velocity coefficient since the latter depends on many parameters such as the Reynolds number, porosity, interface structure, design of perforations, and flow direction. This makes the modeling of such a configuration difficult. The present study proposes an original numerical interface law for a perforated plate. It is used to model the turbulent jet flow interacting with a perforated plate considered as a fictitious porous medium without a detailed description of the perforations. It considers the normal and tangential effects of the flow over the plate. Validation of the model is realized through comparison with experimental data.

关键词： Perforated Plate Porous Medium Wall Jet Air Ventilation Aeraulic turbulence diffusion

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STOCHASTIC THEORY OF THE DISTRIBUTION OF SEDIMENT PARTICLES SUSPENDED IN A TURBULENT FLOW

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International Journal of Sediment Research 1991年第2期 41-59页

作者： SHAO Xuejun and XIA Zhenhuan ①Lecturer, Deportment of Hydraulic Engineering, Tsinghua University, Beijing China ②Professor, Department of Hydraulic Engineering Tsinghua University, Beijing, China

The random motion of sediment particles suspended in a turbulent flow is studied by means of stochastic process. Results of analysis of particle’s frequency response to the random force exerted on the particle due to fluid turbulence suggest that only the lower part of the whole frequency range of the eddy motion will govern the motion of the particle. The mean values of particle velocity and displacement in the vertical direc- tion are calculated and it is found that particle velocity vp- can be decomposed into a mean motion and a velocity fluctuation vp- , where is equal to the fall velocity in tranquil fluid. An Ito^ random differential equation for particle dis- placement Yp is developed, from which a Fokker-Planck equation for the probability density function p(y,t) is derived on the basis of the theory of Markov process, where y denotes the vertical coordinate. The vertical distribution of the particle is thus interrelated to the random motion of the particle. The an effect that a particle will be subject to in the neighborhood or the bottom boundary is taken into consideration and a corresponding Fokker-Planck equation is developed. Analytical solution of the Fok- ker-Planck equation including the lift force effect shows that probability density p(y,t) for the particle displacement has a maximum value at y = H where the perpen- dicular component of the lift force balances the particle gravity. This theoretical result agrees with experimental observations as reported in literature.

关键词： Suspended particles Stochastic theory turbulence diffusion Fre- quency response Probability density function.

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