Modeling Study of Free Overfall in a Rectangular Channel with Strip Roughness

Results from combined laboratory experimental and turbulent numerical modeling studies are presented to investigate the effects of bed roughness (discrete square strips) and slope on the flow over a free overfall in a rectangular channel. A broad range of model parameters such as the bed roughness, channel slope, and incoming upstream Froude number is investigated. The water surface profiles upstream of the brink of the channel, the velocity fields in cavity between two strips, and end depth (water depth at the brink of the channel) are simulated, measured, and discussed for various input conditions. The results show that for a given dimension of bed roughness the relative spacing of roughness (defined as the ratio of the center to center distance to the height of the strip) has a significant effect on the flow. The computational results are in good agreement with the experimental measurements.     

End Depth in U-Shaped Channels: A Simplified Approach

This study presents a simplified approach to determine the end depth of a free overfall in horizontal U-shaped channels. The flow over the free overfall is simulated by that over a sharp-crested weir to calculate the end-depth ratio (EDR). The theoretical model is calibrated by the experimental data by considering the coefficient of velocity a free parameter. The EDR is 0.745 up to nondimensional critical depth 0.50; and then it decreases gradually as the nondimensional critical depth increases. A method to estimate discharge from the end depth is presented. The results obtained using the model agree satisfactorily with the experimental data and results obtained from the previous model of the author.     

Quasi-Theoretical End-Depth-Discharge Relationship for Rectangular Channels

End depth of a free overfall is used as a flow-measuring device in open channels. A quasi-theoretical method for predicting end-depth-ratio (EDR), i.e., ratio of the end depth to the critical depth, and end-depth-discharge (EDD) relationship in terms of pressure coefficient in subcritical and supercritical flows in rectangular channels is presented. The brink pressure distribution coefficient used in the method is evaluated from experimental data. Predicted values of EDR and EDD are compared with the available experimental data.     

Influence of Sluice Gate Contraction Coefficient on Distinguishing Condition

Sluice gates are widely used for flow control in open channels. Flow through the gate may be free or submerged depending on tailwater depth. One may determine whether the flow will be free or submerged by determining the maximum tailwater level that permits free flow. This is called the distinguishing condition. This paper derives a theoretical equation for the distinguishing condition including the contraction coefficient as a parameter, based on the basic equations for free flow and the hydraulic jump. The equation is investigated using experimental data from two different gate types. The results show that the contraction coefficient varies with gate type and that this affects the distinguishing condition. The results also show that for a given upstream depth, tainter gates (radial gates) are less likely to become submerged than vertical gates due to larger contraction coefficients. The present study results are useful in the design and operation of sluice gates.     

Overfall in U-Shaped Channels

Free overfall in U-shaped channels is theoretically analyzed, applying a momentum equation based on the Boussinesq approximation, to obtain the equation of end depth. The end-depth ratio is 0.75 up to normalized critical depth 0.50; and then it decreases gradually with an increase in normalized critical depth. A method to estimate discharge from the end depth is presented. The upstream flow profile of a free overfall is computed using the streamline curvature at the free surface. Experiments were conducted in two U-shaped channels to verify the model. The results obtained using the model agree satisfactorily with the experimental data.     

Dimensionless Stage–Discharge Relationship in Radial Gates

Dimensional analysis was used to obtain stage–discharge relationships under submerged and free flow conditions in radial gates to develop a management tool. Experimental data from a laboratory flume and the indicial method of dimensional analysis were used for this purpose. The resulting equation relates the discharge (or critical depth) to upstream and downstream water depth and gate opening. These equations were then validated by experimental data obtained from field radial gates and compared with the conventional gate equation. Results showed that there was a good agreement between dimensionless equations and field and laboratory data under submerged or free flow conditions. Dimensionless equations are more general and accurate than the conventional ones when there is not an accurate estimation of discharge coefficients.     

End Depth–Discharge Relation at Free Overfall of Trapezoidal Channels

For steady flow near the free overfall (end section) of a horizontal trapezoidal channel, the velocity distribution is nonuniform and the streamlines are curved. An accurate relation between discharge rate and end depth was formulated including these effects. To determine these effects, the streamline pattern in the vertical plane of channel symmetry was determined using measured velocity components and the water surface profile. At the end section, the streamline pattern yielded the streamline curvature, which in turn provided the curvature correction required to predict the true static pressure head profile. The measured static pressure head distribution agreed well with the predicted static pressure head distribution for the end section. The pressure force at the end section was obtained on the basis of the measured static pressure distribution at the end section, and this information yielded a reliable relation between the end depth and the channel discharge rate. Analysis of present and past experimental data indicated that, the pressure head coefficient was the dominant parameter that influences the relationship between discharge rate and end depth in trapezoidal channels. Near the end depth, in the region above the maximum velocity point, the total energy determined from the measured velocity and pressure fields was essentially constant.     

Flow through Side Sluice Gate

The hydraulic characteristics of a side sluice gate were studied experimentally. It was found that the specific energy remains constant along the side sluice gate. The coefficient of discharge for the side sluice gate is related to the main channel Froude number and the ratio of upstream depth of flow to sluice gate opening for free flow. It also depends on an additional parameter: the ratio of tailwater depth to the gate opening for submerged flow. Suitable equations for discharge coefficient are obtained.     

REDA精炼过程钢液流场及循环流量的数值模拟

基于欧拉多相流模型建立REDA精炼过程钢液流动行为的数学模型,并借助计算流体力学软件PHOE- NICS对钢液流动过程进行仿真模拟,重点分析了底吹喷嘴位置、吹氩流量、浸渍管插入深度及浸渍管内径等工艺 参数对REDA精炼过程流场及循环流量的影响。数值模拟结果表明:对于300 t REDA精炼装置底吹喷嘴位置取 1/2 R处为宜,浸渍管插入深度对循环流量影响不显著,扩大浸渍管内径可显著提高钢水循环流量,吹氩流量为1 200 L/min时,钢液循环流量约可达到210 t/min     

Self-Aeration and Friction over Rock Chutes in Uniform Flow Conditions

Interaction between the free surface and the bed material in flow over rock chutes under macroroughness conditions leads to a high air entrainment into the flow. The note reports on an experimental study about air diffusion features in the flow over a long rock chute. Air concentration profiles and water depths over a uniform bed material were measured. An empirical equation for the average air concentration in macroroughness condition for steep slopes is proposed. A new Darcy-Weisbach equivalent friction factor for long chutes as a function of the slope and the relative equivalent depth has also been found.     

Critical Depth Relationships in Developing Open-Channel Flow

Doubts have been expressed about the validity of the critical depth defined in terms of the minimum specific energy head of the free-surface streamline when dealing with developing open-channel flows. This note examines the two approaches for defining critical flow, that based on the minimum specific energy of the free-surface streamline and that based on the mean energy head of the whole flow section. Large differences for the dimensionless critical depths are obtained with the two methods due to each critical depth proving to be a different control point on the free-surface profile. It is argued that both methods are different alternatives, although the critical depth concept was different in each case. Theoretical support to critical flow computations based on the free streamline is provided. An alternative approach for computing the discharge characteristics of broad-crested weirs based on the energy loss inside the boundary layer is also proposed.     

金属粉末注射成形模具浇口对成形性能的影响规律

根据金属粉末注射成形原理，在材料、模具温度等试验条件一致的前提下，将螺旋测试模与0．5～2．1mm之间的6个不同深度尺寸的侧浇口相结合，通过改变注射料熔体温度、注射压力、注射速率等工艺参数，描绘出在不同工艺参数时的侧浇口深度尺寸与阿基米德螺旋线长度的关系曲线，从而研究得到金属粉末注射成形的浇口尺寸与注射料熔体注射成形性能的关系规律：浇口尺寸对金属粉末螺旋线流动长度的影响较大，且不成比例；浇口尺寸与螺旋线流动长度关系曲线(L—H曲线)的变化不是单调的递增或递减，曲线形状呈较为明显的“波浪”形；在一定试验条件下粉末注射成形的理想浇口尺寸值为1．8mm，要偏大于注塑成形的浇口尺寸值；相对注射压力变化时浇口尺寸对L—H曲线关系的影响而言，注射料熔体温度和注射速率的影响相对较小，波动方向一致且较平坦，曲线有微小的上升趋势；当浇口尺寸一定时，工艺参数对流动长度的影响规律与注塑成形中工艺参数的影响规律类似。     

Scour at Submerged Cylindrical Obstacles under Steady Flow

Results of an experimental study on clear-water scour at submerged cylindrical obstacles (circular cylinders) in uniform bed sediments under steady flow are presented. The scour depths at submerged circular cylinders are compared with the scour depths at corresponding unsubmerged cylinders (extended above the free surface of flow) of the same diameters under similar flow and bed sediment conditions. The scour depth decreases with an increase in submergence ratio. A submergence factor is introduced to determine the scour depth at a submerged cylinder from the information of the scour depth at an unsubmerged cylinder of the same diameter. In addition, the flow fields along the upstream vertical plane of symmetry of unsubmerged and submerged cylinders are presented through vector plots, which reveal that the dimension and strength of the horseshoe vortex decreases with an increase in submergence ratio. The horseshoe vortex circulations, which decrease with an increase in submergence ratio, are computed from the vorticity contours by using the Stokes theorem.     

1 850 mm×230 mm板坯连铸结晶器流场与温度场数值模拟

为研究连铸工艺参数对结晶器内部钢液的作用规律,对涟钢1 850 mm×230 mm板坯连铸结晶器流场和温度场进行了系统的数值模拟,研究了不同吹氩量(0～7 L/min)、不同水口浸入深度(110～150 mm)和不同拉速(0.9～1.2 m/min)对结晶器内钢液行为的综合影响。结果表明,随着吹氩量增加,自由液面的钢液流速和温度总体呈现降低的趋势;随着水口浸入深度增加,自由液面的钢液流速先降低后增加;随着拉速增加,自由液面的钢液流速增加;水口浸入深度和拉速对温度场的影响较小。当吹氩量为5 L/min、水口浸入深度为130 mm、拉速为0.9 m/min时,结晶器自由液面具有较小的钢液流速和湍动能,同时液面具有较好的温度均匀性。通过数值模拟研究,为合理选择结晶器相关工艺参数提供了理论依据。     

Minimum Specific Energy and Critical Flow Conditions in Open Channels

In open channels, the relationship between the specific energy and the flow depth exhibits a minimum, and the corresponding flow conditions are called critical flow conditions. Herein they are reanalyzed on the basis of the depth-averaged Bernoulli equation. At critical flow, there is only one possible flow depth, and a new analytical expression of that characteristic depth is developed for ideal-fluid flow situations with nonhydrostatic pressure distribution and nonuniform velocity distribution. The results are applied to relevant critical flow conditions: e.g., at the crest of a spillway. The finding may be applied to predict more accurately the discharge on weir and spillway crests.     

板坯连铸结晶器钢液流场的数值模拟

 运用Fluent软件,对断面150 mm×460 mm的板坯结晶器钢液流场进行了数值模拟,研究了不同水口侧孔面积和长宽比条件下流场的变化情况,并对倾角和插入深度等参数进行了优化。结果表明,长宽比一定时,面积比越大则液面最大速度越小,冲击深度和冲击压力也越小。面积比一定时,大的长宽比有利于减小液面最大速度、冲击压力以及流股对窄面的冲刷。确定了在不改变水口内径、底面形状和出口形状的前提下,适合该结晶器水口的侧孔断面为25 mm×40 mm,倾角为15°,插入深度为200 mm。     

Junction and Drop-Shaft Boundary Conditions for Modeling Free-Surface, Pressurized, and Mixed Free-Surface Pressurized Transient Flows

A junction and drop-shaft boundary conditions (BCs) for one-dimensional modeling of transient flows in single-phase conditions (pure liquid) are formulated, implemented and their accuracy are evaluated using two computational fluid dynamics (CFD) models. The BCs are formulated in the case when mixed flows are simulated using two sets of governing equations, the Saint-Venant equations for the free-surface regions and the compressible water hammer equations for the pressurized regions. The proposed BCs handle all possible flow regimes and their combinations. The flow in each pipe can range from free surface to pressurized flow and the water depth at the junction or drop shaft can take on all possible levels. The BCs are applied to the following three cases: (1) a three-way merging flow; (2) a three-way dividing flow; and (3) a drop shaft connected to a single-horizontal pipe subjected to a rapid variation of the water surface level in the drop shaft. The flow regime for the first two cases range from free surface to pressurized flows, while for the third case, the flow regime is pure pressurized flow. For the third case, laboratory results as well as CFD results were used for evaluating its accuracy. The results suggest that the junction and drop-shaft BCs can be used for modeling transient free-surface, pressurized, and mixed flow conditions with good accuracy.     

高炉炉缸内铁水流动特性的物理模拟

采用原型尺寸且死料柱采用冶金焦堆积而成,针对某实验高炉炉缸铁水流动特性进行水模实验,研究了出铁流量、出铁口深度以及铁水液面高度对铁水流动的影响.研究结果表明,大流量出铁时加剧了铁水对炉缸的流动冲刷,加深出铁口可以减缓这种冲刷,对高炉长寿是有益的.     

The psychophysiology of flow during piano playing.

Expert performance is commonly accompanied by a subjective state of optimal experience called flow. Previous research has shown positive correlations between flow and quality of performance and suggests that flow may function as a reward signal that promotes practice. Here, piano playing was used as a flow-inducing behavior in order to analyze the relationship between subjective flow reports and psychophysiological measures. Professional classical pianists were asked to play a musical piece and then rate state flow. The performance was repeated five times in order to induce a variation in flow, keeping other factors constant, while recording the arterial pulse pressure waveform, respiration, head movements, and activity from the corrugator supercilii and zygomaticus major facial muscles. A significant relation was found between flow and heart period, blood pressure, heart rate variability, activity of the zygomaticus major muscle, and respiratory depth. These findings are discussed in relation to current models of emotion, attention, and expertise, and flow is proposed to be a state of effortless attention, which arises through an interaction between positive affect and high attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)