检索结果-南通市图书馆

Experimental and field study on dissipation coefficient of supersaturated total dissolved gas

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Central South University 2014年第5期21卷 1995-2003页

作者：冯镜洁李然马倩王乐乐 State Key laboratory of hydraulics and Mountain River Engineering(Sichuan University)

The elevated supersaturation of total dissolved gas （TDG） downstream of a high-dam spill has deleterious effects on fish in a large range. A one-dimensional （l-D） longitudinal model is optimal for the prediction of supersaturated TDG dissipation over a long distance. The key issue of the model is to determine the dissipation coefficient accurately. In agreement with field observations and experiment data, dimensional analysis and regression were performed to propose a formula for estimating the dissipation coefficient of supersaturated TDG in various rivers and reservoirs, and it involves the effects of the turbulence intensity, the hydro-pressure and the solid-liquid interface. The friction velocity, water depth, hydraulic radius and Froude number are independent variables in the formula which are easy to determine in practical applications. The 1-D longitudinal model is implemented to calculate the dissipation of TDG in a reach of the Jinsha River. Good agreement is found between the calculated results and field data for both the dissipation coefficient and the dissipation process.

关键词： total dissolved gas dissipation coefficient longitudinal model hydrodynamics

Effects of river width changes on flow characteristics based on flume experiment

在线全文

学校读者我要写书评

暂无评论

Journal of Mountain Science 2016年第2期13卷 361-368页

作者： WANG Xie-kang WANG Bing-jie LIU Xing-nian Zhang Li-qiong State Key laboratory of hydraulics and Mountain River Engineering Sichuan University Hydrology and hydraulics Section South Florida Water Management District

The rapid changes in flow pattern due to varying channel widths will make significantly impact on the hydraulic structures and evolutions of open channel. To better understand the impact of varying width, a flume experiment with adjustable width and a depth-averaged two-dimension numerical model were used to analyze the variations of flow parameters. Our experimental results showed that flow velocity gradually increased with decreasing water depth in converging region, and decreased with increasing water depth in diverging zones. It was also found that the turbulence intensity laws in three directions were not agreed with the theoretical relationships proposed by Nezu and Nakagawa in 1993 in straight open channel flows. The flow in the channel with varying width may change from the supercritical flow to the subcritical flow as a function of Froude number. Our numerical simulations with different flow rates showed that most of the hydraulic jumps in diverging region were submerged jump and the degree of submergence increased with increasing flow rate in gradual channel transition. When the flow rate increased, the range of supercritical flow rapidly decreased and the flow changed from the supercritieal condition to the subcritical condition in diverging sections.

关键词： Gradual channel transition Flow pattern Experimental study Numerical simulation

Effects of Roughness Elements Distribution on Overland Flow Resistance

在线全文

学校读者我要写书评

暂无评论

Journal of Mountain Science 2015年第5期12卷 1145-1156页

作者： YE Chen LIU Xing-nian WANG Xie-kang State Key laboratory of hydraulics and Mountain River Engineering Sichuan University

Roughness elements are various in a mountain area; they include gravel and ground surface vegetation that often result in surface friction drag to resist overland flows. The variation and characteristics of flow resistance strongly impact the overland flow process and watershed floods. In view of the universal existence of natural vegetation, such as Chlorophytum malayense(CM) or Ophiopogon bodinieri(OB), and the sand-gravel bed of the river channel, it is important to understand the role of different types of roughness elements in flow resistance. This study was performed to investigate and compare through flume experiments the behaviors of overland flow resistance by the reaction of multi-scale configuration of different roughness elements. The result showed that the resistance coefficient gradually reduced versus the increase of flow rate in unit width and tended to be a constant when q = 3.0 l/s.m, Fr = 1.0, and Re = 4000 for slopes of 6 to 10 degrees. The gap of the vegetated rough bed and the gravel rough bed is limited to the same as the gap of the two types of vegetation, CM and OB. It was noted that the vegetation contributed to the increase in form resistance negatively and may lead to the mean resistance on decrease. To classify the flow pattern, the laminar flows were described by DarcyWeisbach's equation. In the study the f-Re equation of vegetated bed was developed with f ?5000 *** friction coefficient for laminar flows can be regarded as the critical value for identifying the transformation point of the flow pattern.

关键词： Overland flow Roughness element Flowresistance Reynolds number Chlorophytummalayense Ophiopogon bodinieri

Flow variability along a vegetated natural stream under various sediment transport rates

在线全文

学校读者我要写书评

暂无评论

Journal of Mountain Science 2018年第11期15卷 2347-2364页

作者： WANG Hai-zhou Xu Ze-xing Yu Hai-ti WANG Xie-kang State Key laboratory of hydraulics and Mountain River Engineering Sichuan University

The influence of vegetation and sediment on flow characteristics in open channels cannot be neglected. To study the flow variability under the effects of the instream natural vegetation and sediment supply, experiments were conducted with varied water and sediment supply in a movable bed of a river prototype. The instantaneous threedimensional velocities near two types of vegetation patches(the shrub and the weed) and along the centerline of the main channel with vegetation belts were measured using a 3-D side-looking acoustic Doppler velocimetry. The experimental results show that both the instream vegetation and sediment supply strongly affect the flow and turbulence characteristics. In the case of vegetation patches, both the shrub and weed have a considerable influence on the distribution of the streamwise velocity and turbulence intensity of their surrounding water. The streamwise velocity distribution followed as J-shape and linear shape around the weed and shrub under different experimental conditions. The turbulence intensity was large at the top of the weed and shrub;the shrub had its greatest influence on the downstream water flow. In the case of vegetation belts,the streamwise velocity along the centerline of the main channel exhibited an S-shape, J-shape and linear shape at different locations under varied water,vegetation structures and riverbed *** turbulence intensity along the centerline of the main channel ranged from 0.0 to 0.1. The upstream turbulence intensity was affected considerably by a sediment supply, while the downstream turbulence intensity changed with the varied vegetation characteristics and riverbed topography. The second flow coefficient M-value increased longitudinally and was almost positive along the centerline of the main channel, implying that the rotational direction of the secondary current cell was clockwise.

关键词： Natural vegetation Sediment supply Velocity profile Turbulence intensity Secondary flow Movable bed

Dynamics of loose granular flow and its subsequent deposition in a narrow mountainous river

在线全文

学校读者我要写书评

暂无评论

Journal of Mountain Science 2019年第6期16卷 1367-1380页

作者： LEI Ming XU Ze-xing ZHAO Tao WANG Xie-kang State Key laboratory of hydraulics and Mountain River Engineering Sichuan University

A large amount of loose debris materials were deposited on the slope of mountainous areas after the 2008 Ms 8.0 Wenchuan earthquake. During and after the earthquake, these loose debris deposits collapsed and slide into valleys or rivers, changing river sediment supply condition and channel morphology. To investigate the mechanisms of granular flow and deposition, the dynamics of slope failure and sediment transportation in typical mountainous rivers of different intersection angles were analyzed with a coupling model of Computational Fluid Dynamics and Discrete Element Method(CFD-DEM). The numerical results show that the change of intersection angle between the granular flow flume and the river channel can affect the deposit geometry and the fluid flow field significantly. As the intersection angle increases, the granular velocity perpendicular to the river channel increases, while the granular velocity parallel to the river channel decreases gradually. Compared to the test of dry granular flow, the CFD-DEM coupling tests show much higher granular velocity and larger volume of sediments entrained in the river. Due to the river flow, particles located at the edge of the deposition will move downstream gradually and the main section of sediments deposition moves from the center to the edge of the river channel. As a result, sediment supply in the downstream river will distribute unevenly. Under the erosion of fluid flow, the proportion of fine particles increases, while the proportion of coarse particles decreases gradually in the sediment deposition. The build-up of accumulated sediment mass will cause a significant increase in water level in the river channel, thus creating serious flooding hazard in mountainous rivers.

关键词： Loose debris materials Sediment supply CFD-DEM coupling method Numerical simulations

Evaluation of drag force on a nonuniform particle distribution with a meshless method

在线全文

学校读者我要写书评

暂无评论

Particuology 2011年第3期9卷 288-297页

作者： Xi Wang Changfu You Key laboratory for thermal Science and Power Engineering of Ministry of Education Department of Thermal Engineering Tsinghua University Beijing 100084 China

A meshless Element-Free Galerkin （EFG） method was used to directly simulate the fluidization process in two dimensions. The drag force on particles was obtained by integrating the stress and shear forces on the particle surfaces. The results show that meshless methods are capable of dealing with real particle collisions, thus are superior to most mesh-based methods in reflecting the fluidization process with frequent particle collisions and suitable void fractions. Particle distribution greatly influences the drag coefficients even for the same voidage, that is, there are large differences in the average drag coefficients between nonuniform and uniform particle distributions. Different compacting directions also have different regu- larities, so conventional formulas such as ＇Wen and Yu＇ and ＇Felice＇ models have some deviations in such nonuniform distributions. To evaluate the influence of the nonuniformity, the drag force in multiple particle systems was simulated by using nonuniformity coefficients, Cvx and Cvy, to quantitatively describe the nonuniform distribution in different directions. Drag force during fluidization can be successfully evaluated by the use of Cvx alone.

关键词： Meshless method Drag force Nonuniform particle distribution Nonuniformity coefficient

Adjoint-Based Geometrically Constrained Aerodynamic Optimization of a Transonic Compressor Stage

在线全文

学校读者我要写书评

暂无评论

Journal of thermal Science 2019年第5期28卷 850-861页

作者： SU Xinrong MA Can YUAN Xin Key laboratory for thermal Science and Power Engineering of Ministry of Education Tsinghua University Beijing 100084 China Science and Technology on thermal Energy and Power laboratory Wuhan 430205 China

Efficient method to handle the geometric constraints in the optimization of turbomachinery blade profile is required. Without constraints on the blade thickness, optimal designs typically yield thinner blade to reduce the friction loss, however, at the risk of degraded strength and stiffness. This issue is seldom discussed and existing literature always treat the blade thickness constraint in an indirect manner. In this work, two different geometric constraints on the blade thickness are proposed and applied in the adjoint optimization: one is on the maximum blade thickness and the other is on the blade area. Methods to compute sensitivities of both constraints are proposed and they are integrated into an optimization system based on a finite volume code and a solver for the discrete adjoint equation. Adjoint optimization is conducted to minimize the entropy production in a transonic compressor stage. Results for the adjoint optimization without geometry constraint and two comparative cases are detailed. It is indicated that three cases yield similar performance improvement;however, if geometry constraints are properly handled, the optimal designs have almost the same maximum thickness as the original design, compared to a thinner blade profile with 14% reduction of maximum thickness in the case without geometry constraint. The cases considering geometry constraints also consume slightly reduced Central Processing Unit(CPU) cost. Result of this work verifies the effectiveness of the proposed method to treat geometric constraints in adjoint optimization.

关键词： aerodynamic optimization compressor stage discrete adjoint method geometric constraint

Free-surface air entrainment in open-channel flows

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2017年第6期60卷 893-901页

作者： WEI WangRu XU WeiLin DENG Jun TIAN Zhong ZHANG FaXing State Key laboratory of hydraulics and Mountain River Engineering Sichuan University Chengdu 610065 China

In hydraulic engineering,free-surface aeration is a natural phenomenon occurring in smooth channel *** self-aerated flows,a key aspect that has not yet been well understood is the formation mechanism of free-surface air *** this research,the process of free-surface entrapped deformation is analyzed theoretically and the critical radius of curvature for air entrainment is obtained,affected by flow mean velocity and *** the severity of local free-surface deformation exceeds the critical condition,the entrapped free surface encounters closure in the unstable deformation movement process,resulting in air *** inference agrees well with observed experimental results that are obtained from the processes of surface entrapped deformation and air entrainment captured by a high-speed camera-based data acquisition *** agreement indicates that self-aeration occurs in low-velocity open-channel *** is also confirmed that free-surface turbulent deformation provides a mechanism for air entrainment.

关键词： hydraulic engineering self-aeration turbulence free surface open-channel flows

A HYBRID MODEL FOR SIMULATING VELOCITY FIELD OF A RIVER WITH COMPLEX GEOMETRY PLUNGED BY MULTIPLE JETS

在线全文

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2006年第6期18卷 752-759页

作者： LI Lian-xia LIAO Hua-sheng LI Tian-xiang State Key laboratory of hydraulics and Mountain River Engineering Sichuan University Chengdu 610065China

A hybrid model that combines both physical and numerical models was employed to simulate the velocity field in a river area in complex geometry with multiple plunging jets. The simulation was based on experiments concerning energy dissipation and scour prevention at the Xiluodu Hydropower Station on the Yangtze River. The calculated results indicate that the complex geometry of the river area has a significant influence on the velocity field, especially on the circulation flow pattern at upstream and downstream of the plunging area and on the asymmetric characteristics of the spiral flow near both banks. The scour characteristics of the downstream river bed caused by the multiple jets were also predicted and analyzed according to the characteristics of the calculated velocity field. The good agreement between the simulated and experimental results indicates that the hybrid model can be used to effectively solve complicated 3-D problems with complex geometric and inlet conditions. Such problems may not easily be solved by using either a physical or a numerical model alone, and therefore the method presented in this article is considered to be a practical and effective way of dealing with this kind of problems.

关键词： hybrid models turbulence model scour multiple jets