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Influence of flow field on stability of throttled surge tanks with standpipe

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Journal of Hydrodynamics 2013年第2期25卷 294-299页

作者：安建峰张健俞晓东陈胜 college of water conservancy and hydropower Engineering Hohai University

The steady-state flow field characteristics have important effects on the stability of the throttled surge tank with the standpipe. This paper analyzes these effects on the basis of the numerical simulation of the flow field by using the Computational Fluid Dynamics （CFD） method. It is shown that the anticlockwise recirculation zone is formed in the standpipe, which affects the local head loss at the junction of the standpipe with the pipeline. The variation of the head loss coefficient at the junction is linearly related with the diameter ratio of the standpipe to the pipeline. The dimensionless recirculation flow rate is proportional to the square of the diameter ratio. Considering the effects of the recirculation zone, an empirical expression of the critical stability area is obtained. Comparing with the Thoma critical area, the area obtained by the present method is smaller, and the reduction depends on the diameter ratio and the ratio of the velocity head to the head losses in the tunnel. words：

关键词： critical stability area throttled surge tank Computational Fluid Dynamics (CFD) simulation turbulence model flow field

Influence of bending rigidity of submerged vegetation on local flow resistance

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Journal of Hydrodynamics 2014年第2期26卷 242-249页

作者：吴龙华杨校礼 college of water conservancy and hydropower Engineering Hohai University

The different state of the submerged vegetation has different influences on the flow resistance. This paper explores the relationship between the state and the resistance of an individual submerged vegetation, and the relative bending rigidity of the submerged vegetation is determined by the state of the submerged vegetation. Based on the experimental observations, the state and the resistance of an individual submerged vegetation are analyzed under different inflow conditions. At the same time, the influences of the various submerged vegetations on the flow resistance are discussed under the same inflow conditions. Some interesting relationships are obtained between the flow resistance and the relative bending rigidity of the submerged vegetation, and it is shown that the flow resistance increases with the increase of the relative bending rigidity of the submerged vegetation, and they are positively correlated.

关键词： individual submerged vegetation relative bending rigidity local flow resistance

Large-eddy simulation of suspended sediment transport in turbulent channel flow

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Journal of Hydrodynamics 2013年第1期25卷 48-55页

作者： ZHU Hai WANG Ling-ling TANG Hong-wu college of water conservancy and hydropower Engineering Hohai University

The numerical simulation of the non-cohesive sediment transport in a turbulent channel flow with a high concentration is a challenging but practical task. A modified coherent dynamic eddy model of the Large Eddy Simulation （LES） with a pick-up function is used in the present study to simulate the sediment erosion and the deposition in a turbulent channel flow. The rough wall model is used instead of the LES with the near-wall resolution to obtain the reasonable turbulent flow characteristics while avoiding the high costs in the computation. Good results are obtained, and are used to analyze the sediment transport properties. The results show that the streamwise vortices play an important role in the riverbed erosion and the sediment pick-up, which may serve as guidelines for the sediment management and the water environment protection engineering.

关键词： Large Eddy Simulation (LES) sediment suspension pick-up function turbulent channel flow

Fin characteristics of aerator devices with lateral deflectors

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Journal of Hydrodynamics 2013年第2期25卷 258-263页

作者：吴建华李丹马飞钱尚托 college of water conservancy and hydropower Engineering Hohai University

The fins will be formed if the lateral deflectors in the side-walls with a bottom aerator device are improperly designed, and the flow regime downstream of the aerator device will be worsened. In this paper, the height and the length of the fins induced by the lateral deflectors are theoretically analyzed along with their influencing factors, and the fin characteristics are experimentally investigated on the basis of the theoretical analysis. It is shown that the intensities of the fins are strongly dependent on the ratio of the lateral cavity length to the bottom cavity length, and other factors, like the working head, the height and the angle of the lateral deflector, the flow Froude number around the aerator device, affect the fins indirectly through the changes of the lateral cavity length. When an aerator device with lateral deflectors is designed, it is crucial to match the above mentioned ratio, and to make the ratio of the two cavity lengths less than 1.0 in order to avoid the generation of the fins.

关键词： aerator cavity length fin lateral deflector

Inception point of air entrainment over stepped spillways

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Journal of Hydrodynamics 2013年第1期25卷 91-96页

作者： WU Jian-hua ZHANG Bin MA Fei college of water conservancy and hydropower Engineering Hohai University

The location of the inception point of the air entrainment directly affects the energy dissipation ratio, the cavitation damage control, and the training wall height designs for a stepped spillway and a stilling basin. In this paper, the boundary layer theory of plates is used to predict the location of the inception point of the air entrainment over the stepped spillways by assuming the steps on the spillways as a kind of roughness. An empirical formula is presented based on the physical model experiments, with the maximum error less than 1% except at one point where the error is 1.6%, as compared to the experimental data. Meanwhile, it is shown that the location of the inception point of the air entrainment for the stepped spillway is much nearer to the top of the spillway than that for a smooth spillways, which explains why the high ratio of the energy dissipation is provided for the stepped spillway.

关键词： air entrainment cavitation energy dissipation inception point stepped spillway unit discharge

Transient air-water flow patterns in the vent tube in hydropower tailrace system simulated by 1-D-3-D coupling method

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Journal of Hydrodynamics 2018年第4期30卷 715-721页

作者：王希晨张健俞晓东陈胜 college of water conservancy and hydropower Engineering Hohai University

The vent tube is commonly used for the water hammer protection in the hydropower tailrace system. In transient processes, with air entering and exiting the vent tube, one sees complex hydraulic phenomena, which threaten the station＇s safe operation. It is necessary to investigate the transient mechanisms in the tailrace system with vent tube. In this paper, a 3-D, two-phase numerical model of a vent tube on the connection of the tailrace tunnel and the diversion tunnel, is developed based on the FLUENT with the volume of fluid（VOF） algorithm to investigate the transient air-water flow patterns and the complex hydraulic phenomena in the vent tube of the tailrace system. A 1-D and 3-D unidirectional adjacent coupling（1-D-3-D-UAC） approach with a linear interpolation method is adopted to adjust the timesteps between the 1-D model and the 3-D model on the tunnel inlet and outlet boundaries through the user defined function（UDF）, to transmit the data from the 1-D model to the 3-D model. The model is verified by comparing the results obtained by using the 1-D model alone and from the experiments in literature. The transient flow processes under the full load rejection consist of four stages： the water level dropping stage, the air entering stage, the air pocket collapsing stage, and the air exiting stage. Detailed hydraulic phenomena in the air pocket collapsing process are also discussed.

关键词： Vent tube tailrace tunnel two phase volume of fluid (VOF) 1-D-3-D coupling

Hydraulic characteristics of stepped spillway dropshafts

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Science China(Technological Sciences) 2019年第5期62卷 868-874页

作者： SHEN JieYi WU JianHua MA Fei college of water conservancy and hydropower Engineering Hohai University

Nowadays, "Sponge Cities" are being built to provide a valid solution to the glaring drainage problems in the urban areas of China. The hydraulics of a dropshaft, especially discharge capacity, energy dissipation and cavitation damage control, evidently affect its safety and the city's underground tunnel system, due to the high dropshaft and large discharge. The hydraulic characteristics of stepped spillway dropshafts are experimentally investigated for the variable step rotation angles and end sill heights. Flow regimes inside the dropshafts are classified under the different approach flow discharges. The results illustrate that there is high energy dissipation in the present dropshafts with the stepped spillway and the cavitation damage could be effectively avoided thanks to the effect of the air entrainment to the flow.

关键词： dropshaft end sill height hydraulic characteristics step rotation angle stepped spillway

Stochastic simulation of fluid flow in porous media by the complex variable expression method

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Journal of Hydrodynamics 2013年第2期25卷 215-225页

作者：宋会彬詹美礼盛金昌罗玉龙 college of water conservancy and hydropower Engineering Hohai University

A stochastic simulation of fluid flow in porous media using a complex variable expression method （SFCM） is presented in this paper. Hydraulic conductivity is considered as a random variable and is then expressed in complex variable form, the real part of which is a deterministic value and the imaginary part is a variable value. The stochastic seepage flow is simulated with the SFCM and is compared with the results calculated with the Monte Carlo stochastic finite element method. In using the Monte Carlo method to simulate the stochastic seepage flow field, the hydraulic conductivity is assumed in three different probability distributions using random sampling method. The obtained seepage flow field is examined through skewness analysis, and the skewed distribution probability density function is given. The head mode value and the head comprehensive standard deviation are used to represent the statistics of calculation results obtained by the Monte Carlo method. The stochastic seepage flow field simulated by the SFCM is confirmed to be similar to that given by the Monte Carlo method from numerical aspects. The range of coefficient of variation of hydraulic conductivity in SFCM is larger than used previously in stochastic seepage flow field simulations, and the computation time is short. The results proved that the SFCM is a convenient calculating method for solving the complex problems.

关键词： seepage flow field complex variable expression method (SFCM) stochastic seepage flow Monte Carlo method skewed distribution

Investigation of fluid flow-induced particle migration in granular filters using a DEM-CFD method

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Journal of Hydrodynamics 2014年第3期26卷 406-415页

作者：黄青富詹美礼盛金昌罗玉龙速宝玉 college of water conservancy and hydropower Engineering Hohai University

In embankments and earth dams, the granular filter used to protect the base soil from being eroded by the fluid flow is a major safety device. In this paper, the migration mechanism of the base soil through this type of filters with a fluid flow in the base soil-filter system is studied by using the coupled distinct element method and computational fluid dynamics（DEM-CFD） model. The time-dependent variations of the system parameters such as the total eroded base soil mass, the distribution of the eroded particles within the filter, the porosity, the pore water pressure, and the flow discharge are obtained and analyzed. The conceptions of the trapped particle and the trapped ratio are proposed in order to evaluate the trapped condition of the base soil particles in the filter. The variation of the trapped ratio with time is also analyzed. The results show that the time evolutions of the parameters mentioned above are directly related to the gradation of the filter, which is defined as the representative particle size ratio of the base soil to the filter using an empirical filter design criterion. The feasibility of the model is validated by comparing the numerical results with some experimental and numerical results.

关键词： base soil-filter system distinct element method trapped ratio representative particle size ratio