Flow choking over weir flow slit-type flip buckets

The flow choking may occur for weir flow slit-type flip buckets trader common operation conditions. An estimation method is developed through introducing a comprehensive coefficient to determine the approach flow Froude number for the flow choking to occur in those flip buckets. The error of the present method relative to the experimental data is less than 5%. The results show that, the Froude number for the flow choking to occur is related to the contraction ratio and the contraction angle of the flip buckets. When the flow choking occurs, the upper jet trajectory decreases and the lower one is almost not affected, and the dynamic pressures on the bottom and the sidewalls increase due to the flow profile rising on the flip buckets.

Fluid Flow in Tundish Due to Different Type Arrangement of Weir and Dam

Tundish is an important metallurgical reactor in the continuous castingprocess. In order to control the fluid flow in tundish and thus take full advantage of the residencetime available for the removal of inclusions from molten steel, the effect of weir and dam on thefluid flow has been studied in a water model based on the characteristic number Froude and Reynoldnumber similarity criteria. The residence time distribution curves of the flow were measured bySG800. The optimum arrangement of darn and weir and the nonstationary flow in tundish werediscussed. The results show that the combination of weir and dam is benefit for the flow pattern intundish, weir can prevent the upper recirculating flow, dam can cut off the bottom flow and turn toupwards, it is advantageous to separate the nonmetallic inclusions. Furthermore, it is important toexceed the critical depth of bath during exchange ladles, not only for the inclusion floatation butalso for avoiding tundish slag drainage earlier.

NUMERICAL AND EXPERIMENTAL INVESTIGATION OF FLOW OVER A SEMICIRCULAR WEIR

The water flow over a semicircular weir is investigated numerically and experimentally in this paper. The numerical model solves the Reynolds equation for a mean flow field with thek-ε-turbulent model. To trace the motion of the free surface, the COF method with geometric reconstruction is employed. The velocity of the flow is measured by means of LDV technique. Four types of flow patterns, the position of the separation and reattachment point, the distribution of shear stress on the bed at downstream of the weir are presented and discussed. The numerical results agree well with the experiment data.

Numerical Study on Hydraulic Characteristics and Discharge Capacity of Modified Piano Key Weir with Various Inlet/Outlet Width Ratio

A modified piano key weir with a rounded nose and a parapet wall (MPKW) can improve the discharge capacity significantly compared to a standard piano key weir. However, the optimum of the inlet/outlet width ratio (Wi/Wo) on the discharge efficiency of MPKW is still not investigated numerically. The present work utilized the numerical modeling to investigate and analyze the effects of the inlet/outlet key width ratios on the hydraulic characteristics and discharge capacity of the MPKW. To validate the numerical model with the experimental data, the results indicate that the average relative error is 2.96%, which confirms that the numerical model is fairly well to predictthe specifications of flow over on the MPKW. Numerical simulation results indicated that the discharge capacity of the MPKW can be improved up to 8.5% by optimizing the Wi/Wo ratio ranging from 1.53 to 1.67 even if the other parameters of the MPKW keep unchanged. A big Wi/Wo ratio generally leads to an increase in discharge capacity at low heads and a little effect on the discharge efficiency at high heads. The discharge efficiency of the inlet and outlet crests increases up to 9.6% for high heads, while discharge efficiency of the lateral crest decreases up to 23.5% compared with the reference model. The findings of the study revealed that the intrinsic influencing mechanism of the Wi/Wo ratio on the discharge performance of MPKWs.

龙游灵山港姜席堰河段水动力特性计算分析

为量化姜席堰河段水动力机制,结合步坑口水文站的水文资料与实际调查情况,运用现代水力学原理及数值模拟方法对姜席堰河段的水动力学机理进行推演,比较了上游不同来流量情况下,内外江的分流比、沿程流速、水位和流场变化,确定了姜席堰河段具体的分流机制以及可能产生冲刷与淤积的工程隐患点。基于模拟结果,推求了姜堰和席堰的流量系数,得出了姜堰与席堰的堰流公式,为姜席堰河段治理与防护提供了理论依据。

建筑屋面方形溢流口溢流量计算公式分析及探究

建筑屋面溢流口的设计计算关系到屋面结构安全,对现有国家规范中墙体方形溢流口溢流量计算公式进行了分析对比,通过对水力学不同堰流形式、宽顶堰基本计算公式、流量系数及侧收缩系数等方面的分析推导,得出按现有规范公式计算出的溢流口几何尺寸偏小。结合屋面不同雨水斗对斗前水深的要求及建筑屋面的不同排水形式,提出了墙体方形溢流口属于宽顶堰,明确了溢流口的溢流水位高度和上游坎高度的取值范围,进而采用数学工具推出了屋面方形溢流口溢流量新的计算公式,并从水力学和数学角度对新公式进行了合理性分析,可供设计同行参考。

实用堰法在郝家店水文站流量自动推求中的应用研究

本文以郝家店水文站为实例,采用实用堰流公式计算实用堰流量系数,建立水位~堰流量系数曲线,并通过水位遥测数据来实现流量自动推求。结果表明,通过实用堰流公式推求的郝家店水文站流量的系统误差为-0.30%,可满足误差允许要求。该研究成果对于水文站流量自动推求方式具有参考价值。

Design optimization of flow control device for multi-strand tundish

The fluid flow phenomena in tundish have a strong influence not only on theuniform of composition and temperature of bath, but also on the separation of non-metallicinclusions, especially for the multi-strand tundish. A water model of a multi-strand tundish hasbeen set up based on the Froude number and Reynold number similarity criteria. The effect ofdam+weir and baffle on the uniform of composition and temperature of bath for different nozzles hasbeen studied. The residence time distribution curves of the fluid flow were measured by SG800.Comparing the photos of the flow pattern in tundish, the optimum arrangement of baffle+dam wasobtained. This new structure is benefit not only to uniform the temperature among different SENs(submerge entry nozzles) but also to separate the non-inclusions from the liquid steel, it can bewidely used in multi-strand tundish.

Water Modeling of Optimizing Tundish Flow Field

In the water modeling experiments, three cases were considered, i. e, , a bare tundish, a tundish equipped with a turbulence inhibitor, and a rectangular tundish equipped with weirs （dams） and a turbulence inhibitor. Comparing the RTD curves, inclusion separation, and the result of the streamline experiment, it can be found that the tundish equipped with weirs （dams） and a turbulence inhibitor has a great effect on the flow field and the inclusion separation when compared with the sole use or no use of the turbulent inhibitor or weirs （dams）. In addition, the enlargement of the distance between the weir and dam will result in a better effect when the tundish equipped with weirs （dam） and a turbulence inhibitor was used.

An Experimental Study on the Dissipation Effect of a Baffle Downstream of a Weir

This study is an experimental study to analyze the dissipation effect of a baffle shape installed to reduce the scour problem downstream of a weir. The hydraulic experiment on the flow dissipation effect created by baffle installation was an experiment under a fixed bed condition to investigate the flow dissipation effect based on changes in flow in the apron downstream caused by?changes in baffle shape. The experimental analysis was conducted by measuring the flow rate at the apron downstream with and without the installation of a baffle on the basis of the flow dissipation effect. This experiment compared the flow dissipation effect achieved with five baffle shapes to analyze the effect of the baffle shape. Two conditions of flow rate were considered: when a water level in the area of super-critical flow was lower than the baffle height, and when it?flowed over the baffle. Overall, the flow dissipation effect was found to be?good when a square baffle with a large flow blocking area was used. The analysis also found that hydraulic jump was facilitated when the front part of the baffle was inclined, as flow was induced to the upper direction. The result of the experiment showed that when performing flow dissipation through the use of a baffle, the effect of flow blocking and flow duration alteration should be considered.

低水头拦河水闸折线型实用堰流计算分析

低水头拦河水闸闸室堰型一般可分为宽顶堰和实用堰2种,而其实用堰主要为折线型的低堰。目前,拦河水闸闸室宽顶堰堰流的水力计算方法较完善,折线型实用堰堰流水力计算方法尚不够成熟和完善。在综合分析拦河水闸折线型实用堰的低堰、工程布置、工程运行实际状况等特点和因素的基础上,取得主要成果为:满足该文工程所述特点(低堰、设置上游铺盖和闸墩等)的水闸折线型实用堰的堰流呈现为宽顶堰堰流,其淹没界限判别和淹没系数计算可采用宽顶堰流相同的方法。研究成果得到了相关工程水力模型试验成果的验证,可供类似工程设计和运行参考。

琴键堰增设护墙对泄流能力影响的模型试验研究

为探究在堰顶增设护墙以及护墙高度对琴键堰泄流能力的影响,通过模型试验对比分析了8种不同高度护墙琴键堰的泄流能力,并通过数值模拟对5种不同高度护墙琴键堰各溢流前缘的泄流量、水面形态以及流速分布等特征进行了分析。结果表明:相较于基础体型,增设护墙提高了进口和出口宫室的泄流效率和泄流量占比,提高了侧堰泄流量,减少了侧堰溢流碰撞,提高了水流下泄流速,从而提升了琴键堰的泄流能力;增设护墙高度为堰高的13%时,泄流能力提升最大,当相对水头H/P<0.20、0.20<H/P<0.40时泄流能力可分别提升8%~15%和10%~12%。

臂坡对堰槽组合设施紊流结构影响试验研究

堰槽组合设施在山区河流流量监测中具有很大优势,臂坡作为其关键形状参数,可以调节堰槽组合设施内水动力特性,改变堰后泥沙沉积分布和下游冲刷形态。为进一步探索臂坡对堰槽组合设施水流紊动特性的影响,通过室内试验,分析不同臂坡、来流强度及底坡因素影响下的底层水流特性变化,探究流速、紊动能、床面切应力等参数分布规律,揭示堰槽组合设施运行过程中水流能量耗散及冲刷机理。研究结果表明:臂坡影响流量的横向分布,臂坡增大加剧水流聚中,使两侧堰后水流下切回流增强,增加溯源冲刷风险;臂坡和底坡增大导致堰后两侧紊动强度及紊动能增大,加剧了堰下水流能量耗散,有效提高了设施的消能率;相比雷诺切应力法,设施后床面剪切应力计算更适合采用修正紊动能法且床面剪切应力较大值主要集中在两侧堰后区域;大尺度涡结构主要集中在排淤量水槽出口两侧,而其他涡区分布在两侧堰后区域。

量水槽出口宽度对堰槽组合量水设施过流能力的影响

【目的】研究量水槽出口宽度对堰槽组合量水设施水力性能及对测流的影响,为扩大堰槽组合量水设施的适用性提供参考。【方法】对3种量水槽出口宽度(b=25,35和45 cm)在不同流量(5~71 L/s)下的35种工况进行水力性能试验,通过中垂面30个测点的水深及垂线平均流速变化,分析出口宽度对设施中垂面水面线和佛汝德数(Fr)沿程变化的影响,明确槽内流和堰槽流的流量阈值;根据流量(Q)与量水槽内测点水深的相关性,分析量水槽出口宽度对流量系数的影响,并建立不同量水槽出口宽度下的流量公式。【结果】3种量水槽出口宽度条件下,中垂面水深和Fr的沿程变化均表现出相似的规律,即中垂面水深在上游段表现稳定,进入量水槽后逐渐下降至出口后的薄水层区域;Fr值在上游段相对平稳,保持在0.1~0.2,进入量水槽后逐渐增大至最大值1.2~1.5,且增大速率沿程变大。上游段的水深和量水槽内的水深均随量水槽出口宽度的增加而减小,出口段、薄水层区域和下游壅水区域的水深受量水槽出口宽度影响不大。上游段至量水槽内部过渡扭面段的Fr值随量水槽出口宽度的增加而增大,量水槽内部梯形窄段的Fr值随着出口宽度的增加而减小。同一量水槽出口宽度下,槽内流的流量系数随流量的增加而增大,堰槽流的流量系数随流量的增加而减小。同一相对作用水头下,槽内流的流量系数随量水槽出口宽度的增加而减小,堰槽流的流量系数随出口宽度的增加而增大。基于建立的3种量水槽出口宽度下的流量公式,得到的流量计算值与实测值的相对误差均在2%以内,使堰槽组合量水设施的适用范围进一步扩大。【结论】量水槽出口宽度对上游和量水槽内的水深有明显影响,出口宽度的增加能够增大堰槽组合量水设施的流量阈值及过流能力,并使临界水深的断面位置向下游推移。

淤地坝泥沙淤积高度对宽顶堰水力特性的影响

为解决淤地坝长期运行,泥沙不断沉积超出设计库容,漫延至溢洪道内并在宽顶堰前堆积从而影响泄流的问题,该研究通过物理模型试验的方法,对不同淤积高度下溢洪道内宽顶堰的水流流态、水面线、流速分布、流量系数等特性进行对比分析。结果表明,随着淤积高度的增加,堰流在保持宽顶堰原有的过流形态同时壅水程度逐渐降低;淤积高度的不同会影响堰前及堰上区域的水面高程和断面流速,堰前水位随着淤积高度的增加略微下降,过流断面逐渐减小,水流流速增大;随着淤积高度的增加,流量系数逐渐增大,即宽顶堰的泄流能力有所增强。因此引入参数相对淤积高度(淤积高度S与堰高P之比),根据试验数据拟合得到了淤积工况下宽顶堰流量系数经验公式,计算流量与实测流量的平均相对误差为2.7%,满足精度要求,可为淤地坝除险加固工程的相关工作提供参考。

高原环境下WES剖面实用堰流量系数分析

本文依托西藏农牧学院-多功能变坡水槽,以WES剖面型实用堰为模型开展堰流流量系数测定实验,改变流量测得相应的堰顶水头H和断面流速v0,计算出堰顶全水头H0和相应流量系数m值,并对海拔3000 m地区WES剖面型实用堰流量系数经验公式进行拟合。结果表明:当上游堰高P1/设计水头Hd=1时,在海拔3000 m时WES剖面型实用堰流量系数m随堰顶全水头H_(0)与设计水头Hd比值的增大而增大,与海拔30 m相比,二者变化趋势大致相同,但是同一比值情况下,海拔在3000 m时流量系数要大于海拔30 m时的流量系数,最大差值可达4.60%;海拔3000 m地区WES剖面型实用堰流量系数经验公式为m=0.03963(H_(0)/H_(d))^(3)-0.17984(H_(0)/H_(d))^(2)+0.29027(H_(0)/H_(d))+0.34957,经验公式计算流量与实测流量之间最大绝对百分误差为3.32%。

堰槽组合量水设施水力性能数值模拟研究

【目的】堰槽组合量水设施适用于流量变幅较大的山区溪流流量测量,以数值模拟的手段全面分析其流场分布规律和水力特性,以期为堰槽组合量水设施的结构优化提供理论依据。【方法】在模型试验的基础上,采用FLOW-3D软件对10.13~200.00 L/s(试验最大流量的2.8倍)范围内的17种流量工况下该设施的水力性能进行数值模拟,分析了槽内流和堰槽流的沿程水深、佛汝德数(Fr)及流速的变化规律。【结果】所有流量工况下堰槽组合量水设施中心纵剖面Fr和流速均沿程先增大后减小,呈单峰分布;设施上游水流平稳,Fr为0.1~0.3,流速为0.08~0.5 m/s,随流量的增加逐渐加大;水流进入该设施后,Fr和流速急剧增大;设施下游出现较大范围的薄水层区域,Fr最大值达到3.0~4.6,流速最大值为1.05~2.06m/s;槽内流时下游产生弱水跃,堰槽流时下游均为急流(Fr>1),同时扩散水流在侧岸处发生折冲,产生菱形波;流量小于100 L/s时,模型试验建立的测流公式最大相对误差为6.11%,流量超过100L/s时,相对误差逐渐增大。对流量大于100L/s的模拟结果进行分析,建立了流量大于100L/s时的测流公式,该公式相对误差小于0.87%,满足河流量水要求。【结论】基于FLOW-3D软件对堰槽组合量水设施进行的水力性能数值模拟与模型试验有着较好的一致性,建立了大流量下的测流公式,扩充了堰槽组合量水设施的测量范围。

肯尼亚某迷宫堰溢洪道水力特性

受泄洪要求、地质条件、用地规模、供电水平、运行管理等条件约束,肯尼亚某大坝供水项目溢洪道控制段设计拟由有闸控制的宽顶堰方案调整为无人值守的迷宫堰方案。为确保泄洪能力满足原设计要求,尽可能减少工程投资,并降低溢洪道方案的修改对大坝工程的影响,按现有工程经验初拟迷宫堰设计堰高、堰宽、展长等参数,采用Flow-3D软件模拟分析溢洪道泄流工况,根据数值模拟结果最终确定设计参数后,进行模型试验加以验证。数值模拟成果及模型试验结果表明:在堰上水头小于堰高时,迷宫堰综合流量系数随堰上水头的增加呈现先增后减的趋势;迷宫堰溢洪道泄流时无明显不良流态,且具有很高的过流能力,满足特殊要求下工程应用要求。

保水堰体型参数对过流能力影响的数值模拟

保水堰是一种新型溢流堰结构形式,为提升保水堰在大型调水工程中的输水能力,利用实测数据进行模型验证,在确保模拟保水堰堰内水流流态规律准确性的前提下,探究工程中保水堰体型参数对输水系统过流能力的影响。研究揭示了堰井段环状旋涡区的产生与发展机理,并对11种降低堰高方案进行数值计算,分析堰井段流速矢量分布和环状旋涡区范围及能量耗散的变化,发现使输水系统过流能力增加的最佳堰高区间为[1.0 P_(1)≥P≥0.7P_(1)](P为保水堰堰高;P_(1)为堰前堰高)。当堰高在此区间内,通过降低P使堰前流速矢量仰角和堰后环状旋涡区变小,能量耗散显著降低,降低0.1P_(1),流量平均增加2.1%。考虑到工程改造成本和过流能力提升效果,故在本研究提出最佳堰高区间内修改保水堰的结构,为输水系统过流能力提升提供参考。