水工隧洞阶梯消能机理及水力特性研究

发布时间：2018-07-05 09:44

本文选题：无压隧洞 + 阶梯式消能工　；参考：《武汉大学》2014年博士论文

【摘要】：隧洞作为水利枢纽泄洪的主要建筑物之一,在泄洪中发挥着重要的作用,但很多无压隧洞受到地形和地质因素的影响,不仅底坡较大,而且洞身较长,隧洞进出口水头差较大,水流入洞后流速很快超过16m/s,属于高流速隧洞[7],因此需要设置消能工进行能量控制。传统的消能方式只能在隧洞进口之前和出口之后发挥作用,对洞身不能起到保护作用。另外部分工程由于地形限制,下游没有足够空间修筑底流消能工,且不具备挑流消能条件,如果能在洞内采用阶梯消能工,将隧洞中将大量能量消杀掉,就可以为工程带来巨大的效益。本文通过模型试验结合数值模拟的研究方法,从水流流况、流态、水面线、阶梯水平面和阶梯竖直面的时均压力和脉动压力、断面水深方向以及沿程阶梯掺气特性、绝对消能效果等方面对水工隧洞阶梯消能机理及水力特性进行较为系统的研究,论文主要内容如下： 1.水工隧洞阶梯消能的流况研究。本文提出水工隧洞阶梯消能水流可分为跌落水流、过渡水流、滑行水流三种流况,水工隧洞中水流弗氏数的变化范围较溢洪道要广泛许多,试验中观察到在单宽流量相同的条件下,泄槽首部弗氏数不同,沿程阶梯会出现不同的流况,指出流况界限与泄槽首部水流弗氏数有密切联系,提出跌落水流和滑行水流界限的经验公式。 2.隧洞阶梯消能工首部设置较小的楔形阶梯对水流影响的研究。在首部设置较小的楔形阶梯,如前3级阶梯高度h=0.5m,3-10级阶梯h=0.5-1.0m,10级以后h=1.0-2.0m,同时将首部阶梯水平面设置为向下游倾斜的楔形阶梯,然后渐变为水平阶梯。这样一方面可以降低发生滑行水流的单宽流量,使水流容易发生滑行水流；另一方面,楔形阶梯减小跌落水舌与阶梯水平面的夹角,从而减小水舌与底板之间的冲击力,使得水面较平稳,从而改善了挑射水流等不利流态。 3.连续坎后设置圆弧形底坡或者渥奇曲线底坡解决掺气坎后积水问题的研究。缓底坡低Fr数水流很容易出现掺气坎积水问题,研究发现挑射水舌需落在弧形底坡或者渥奇曲线底坡的中部偏尾部,否则曲线形底坡不能起到抑制水流回溯的作用。圆弧型底坡或者渥奇曲线底坡体型,在相同水平长度下,曲线的高差越大,越有利消除积水。渥奇曲线相对圆弧曲线底坡,首部坡度小、中后部坡度大,比圆弧曲线更能抑制水流的回溯,完全消除空腔内的积水,提高掺气槽的掺气效率。 4.掺气坎通气量qs与单宽流量q以及水流弗氏数Fr三者之间关联规律的研究。通过系统的研究,提出相应的经验公式。工程设计中,根据工程运行时最大的流量,以及水流运行时可能出现的最大弗氏数,计算出掺气坎通气量,确定掺气槽尺寸。 5.掺气均匀点位置以及隧洞阶梯消能工掺气特性研究。研究发现,掺气均匀点距离掺气坎的距离Ls/h与掺气坎上游处水流的流能比F之间具有一定的函数关系,作者提出自己的经验公式。单个阶梯沿水深方向的掺气规律为：掺气浓度从底板至水面的规律为0.1-0.3倍水深区间先缓慢增大,在0.4-0.6倍水深区间,掺气浓度有较大幅度的减小,在0.8倍水深至水面处时,掺气浓度逐渐增加。随着单宽流量的增加,水深方向整体掺气浓度减小,随着水流弗氏数、底坡坡度、阶梯高度的增大整体掺气浓度增加。其中弗氏数的变化,对上游阶梯中部水深掺气浓度影响较显著,底坡坡度和阶梯高度对同一断面沿水深方向的掺气浓度分布规律基本无影响,底坡坡度对水流表面和中部的掺气浓度影响较底部要大。 6.沿程阶梯水流弗氏数变化规律的研究。研究发现水流平均弗氏数在阶梯首部波动较大,沿程会逐渐趋于稳定。单宽流量越大,沿程阶梯弗氏数越早趋于稳定,且稳定后相对弗氏数f2/Fr1越大。随着泄槽首部弗氏数的提升,沿程阶梯相对弗氏数显著降低,沿程阶梯弗氏数越较早的达到稳定值。随着底坡和阶梯高度的增加,沿程阶梯相对弗氏数逐渐增大,沿程波动性越大,弗氏数达到稳定的位置相应滞后。下游水流相对弗氏数一般在10级左右阶梯处达到稳定值。 7.水工隧洞阶梯消能率计算公式的研究。从阶梯消能工绝对消能率的公式出发,在泄槽首部水流条件一定的条件下,等价的推导出沿程阶梯的绝对消能率为下游阶梯水流断面平均弗氏数Fr2的函数。系统的研究单宽流量q、泄槽首部水流弗氏数Fr1、底坡坡度i、阶梯高度h对沿程阶梯处水流弗氏数Fr2的影响,从而推导出绝对消能率的计算公式,计算公式与实测数据吻合,从本质上指出阶梯消能过程就是减小沿程水流弗氏数。 8.水工隧洞阶梯消能率影响因素的研究。从阶梯布置长度、单宽流量、水流弗氏数、底坡坡度、阶梯高度等影响因素进行研究。随着阶梯布置长度的增加,沿程消能率呈现非线性的增大,增长速度逐渐变慢。在沿程阶梯的同一部位,随着流量的增大,消能率逐渐减小,随着泄槽底坡的增大,消能率基本呈现线性减小,随着泄槽首部水流弗氏数的增大,同一部位的消能率呈现先降低后有所回升,弗氏数的改变显著的影响上游阶梯的消能率,对尾部阶梯消能率影响不明显。当沿程阶梯水流弗氏数达到稳定值后,同一部位的消能率基本与阶梯高度无关。同时研究结果表明不能明确的判别跌落水流和滑行水流的消能率何者更优,三种流况的消能率大小要根据引起流况改变的因素来判别。 9.水工隧洞阶梯消能工设计中合适的阶梯布置长度和阶梯体型的研究。从函数的增减性可以推断,消能率η是相对断面高差△H1-2/y1的单调递增凹函数。在阶梯长度布置达到一定长度后,继续增加阶梯长度来提高消能率是不经济的。阶梯高度较大时,沿程阶梯水流波动性较大,沿程阶梯弗氏数达到稳定所需要的阶梯数量较多,考虑到弗氏数达到稳定值后,阶梯高度对消能率基本无影响,因而在设计阶梯消能工时,首部阶梯采用较小楔形阶梯。坡度较陡且单宽流量较大时,要达到较高的消能率,需要布置较多的阶梯,约50-130级阶梯,在实际工程中施工的工程量较多,这类工程基本不适合采用阶梯消能工。 10.水工隧洞阶梯消能工空蚀、冲刷、振动等安全性问题的研究。时均压力和脉动压力是引起以上安全性问题关键因素。本文系统从单宽流量、水流弗氏数、底坡坡度、阶梯高度四个主要影响因素对阶梯水平面和竖直面的时均压力、脉动压强强度、脉动压强最大及最小瞬时值、脉动功率谱等水力参数进行研究。研究结果表明：阶梯水平面最大值时均压强p/h=3.5,最大瞬时压强p/h=9.5。第一级阶梯凸角最大负压p/h=-0.8,沿程阶梯最大负压p/h=-0.6,沿程阶梯凸角区域脉动压强最小瞬时值p/h=-2.5m。在水流掺气充分的情况下,阶梯水平面最大正压及阶梯竖直面最大负压均在混凝土的安全承受能力范围内,基本不会出现空蚀冲刷破坏。阶梯消能工上水流的脉动主频与阶梯边壁、底板固有频率相差较大,不会引起阶梯消能工的强烈振动。实际水工隧洞中设计阶梯阶梯消能工时,阶梯体型和阶梯布置长度要综合考虑流态、掺气特性、消能效果,单方面的追求高消能率会增加不必要的成本。如果水工隧洞空间充足,应尽量使水流形成滑行水流,中部及下游阶梯水流进入充分掺气区,同时控制水工隧洞出口的消能率,使其在与下游水流衔接时不对下游河床和岸坡造成冲刷破坏。如果水工隧洞空间受到限制,首先考虑消能效果和水流流态,其次考虑能否使水流均匀掺气。
[Abstract]:As one of the main buildings in flood discharge, the tunnel plays an important role in flood discharge. However, many non pressure tunnels are affected by terrain and geological factors, not only the bottom slope is larger, but also the hole is long, and the head of the tunnel has a long head difference. The flow velocity of the tunnel is faster than 16m/s, and it belongs to the high velocity tunnel [7]. Therefore, it is necessary to set up a high velocity tunnel. The traditional energy dissipation method can only play the role before and after the entrance and exit of the tunnel, and can not protect the hole. In the other part of the project, there is not enough space to build the bottom flow energy dissipator in the downstream, and the downstream energy dissipation conditions are not enough, and if the stair energy dissipator can be used in the tunnel, the energy dissipator can be used in the tunnel. A large amount of energy will be killed in the tunnel, which will bring great benefits to the project.
In this paper, through the method of model test and numerical simulation, the time average pressure and pulsation pressure of water flow state, flow state, water surface line, step horizontal plane and staircase vertical face, the direction of the depth of section water, the aeration characteristics along the ladder and the absolute energy dissipation effect on the energy dissipation mechanism and hydraulic characteristics of the staircase of hydraulic tunnel are comparatively systematic. The main contents of the thesis are as follows:
Study on the flow of staircase energy dissipation in 1. hydraulic tunnels. This paper proposes that the staircase energy dissipation flow of the hydraulic tunnel can be divided into three kinds of flow conditions, such as falling water, transition flow, and gliding flow. The variation range of the number of Freudian flow in the hydraulic tunnel is much wider than that in the spillway. There will be different flow conditions along the staircase, and it is pointed out that the flow condition is closely related to the first flow of the flute, and the empirical formula of the boundary between the falling water flow and the sliding flow is put forward.
The first part of the 2. tunnel staircase energy dissipator is the first to set up a small wedge step to study the influence of the flow on the flow. In the first set of smaller wedge-shaped steps, such as the first 3 step height h=0.5m, the 3-10 step h=0.5-1.0m, and the later h=1.0-2.0m, the first step horizontal plane is set to the downstream wedge ladder and then gradually to the horizontal step. On the one hand, the single wide flow of the sliding flow can be reduced and the flow of water can easily occur. On the other hand, the wedge step reduces the angle between the falling water tongue and the horizontal plane, thus reducing the impact force between the water tongue and the bottom plate, making the water surface more stable, thus improving the unfavorable flow and so on.
The research on the problem of water accumulation after the aeration ridge is solved by setting the circular arc bottom slope or the bottom slope of Walch curve after 3. continuous sill. The problem of water aeration is easy to appear at low Fr number flow in slow bottom slope. It is found that the pitched water tongue should fall on the bottom of the curved bottom slope or the bottom of the bottom slope of the Walch curve, and the curve bottom slope can not be used to suppress the backtracking of the flow. In the same horizontal length, the higher the height difference of the curve, the greater the height difference of the curve, the more favorable to eliminate the water accumulation. The lower slope of the walker curve is relative to the arc curve, the lower slope of the first part, the larger slope in the middle and the rear, can restrain the backtracking of the flow more than the arc curve, completely eliminate the water accumulation in the cavity and improve the aeration efficiency of the aerated trough. Rate.
The study of the correlation between the 4. gas flow rate QS and the single wide flow Q and the flick number Fr three. Through the systematic study, the corresponding empirical formula is put forward. In the engineering design, the air volume of aeration and the size of the aeration tank are calculated according to the maximum flow rate and the maximum Freund number that may appear during the operation of the water.
It is found that there is a certain function relationship between the distance Ls/h of the air entrainment and the flow energy of the flow in the upstream of the aeration point Ls/h and the flow energy of the flow at the upper reaches of the aeration ridge. The author puts forward his own empirical formula. The air mixing law of a single step along the direction of water depth is: the concentration of aeration from the bottom to the bottom. The regularity of the plate to the water surface is a slow increase in the depth of 0.1-0.3 times, and the concentration of aeration is greatly reduced at the depth of 0.4-0.6 times. When the water depth is 0.8 times to the surface of the water, the concentration of aeration gradually increases. With the increase of the single width of the water, the concentration of the whole aeration in the direction of water depth decreases, with the increase of the number of water flow, the slope of the bottom and the step height. The change of Freund number has a significant influence on the air concentration in the upper reaches of the upper reaches of the upper reaches. The slope and step height of the bottom slope have no influence on the gas concentration distribution along the direction of water depth. The influence of the slope gradient on the air concentration in the flow surface and the middle is larger than that in the bottom.
The study of the change law of the number of Freund number in the 6. staircase flow. The study found that the average Freund number in the first part of the water flow fluctuates larger in the first part of the ladder, and gradually tends to be stable along the path. The greater the flow of the single width, the earlier the Freund number tends to be stable, and the relative Freudian number f2/Fr1 becomes larger after the stability. With the increase of the number of Freund numbers along the ladder, the number of Freund is gradually increased with the increase of the bottom slope and the ladder height, the greater the fluctuation along the path, the more stable position of the Freund number, and the relative fund number in the downstream water reaches a stable value at about 10 steps.
7. formula for calculating the staircase energy dissipation rate of hydraulic tunnel. Starting from the formula of absolute energy dissipation of staircase energy dissipator, under the condition of a certain flow condition of the first flow of the slots, the equivalent derivation of the absolute energy dissipation rate of the stepped staircase is a function of the average Freund number Fr2 of the downstream staircase flow section. The system has a single wide flow of Q and the first flute of the slots. The influence of the number of Fr1, the slope of the bottom slope I and the step height h on the number Fr2 of the flow in the staircase along the distance, thus derives the calculation formula of the absolute energy dissipation rate. The formula is in agreement with the measured data. In essence, it is pointed out that the step energy dissipation process is to reduce the number of Freund in the flow.
The study of factors affecting the staircase energy dissipation rate of 8. hydraulic tunnel. From step layout length, single width flow, flick number, bottom slope, step height and other influence factors. With the increase of the ladder length, the energy dissipation rate along the distance increases and the growth rate gradually slows down. In the same part of the ladder, with the flow rate The energy dissipation rate decreases gradually. With the increase of the bottom slope of the slots, the energy dissipation rate basically presents a linear decrease. With the increase of the first flow of the flute, the energy dissipation rate of the same part decreases first and then rises, and the change of the Freund number significantly affects the energy dissipation rate of the upper ladder, and the effect on the staircase energy dissipation rate is not obvious. At the same time, the energy dissipation rate of the same part is basically independent of the step height. At the same time, the results show that the energy dissipation rate of the falling water flow and the sliding flow can not be distinguished clearly. The energy dissipation rate of the three flow conditions should be judged according to the factors that cause the change of the flow condition.
The study of the appropriate ladder layout length and staircase shape in the design of 9. hydraulic tunnel staircase dissipator. From the increase and subtraction of the function, the energy dissipation rate is a monotonically increasing concave function of the relative height difference Delta H1-2/y1. After the ladder length is arranged to a certain length, it is not economical to continue to increase the step length to increase the energy dissipation rate. When the height is high, the fluctuation of the flow along the ladder is larger and the number of steps required to reach stability is more. Considering that the number reaches stable value, the ladder height has no effect on the energy dissipation. Therefore, the first step adopts a smaller wedge step in the design of staircase energy dissipation. When the slope is steep and the single width flow is larger, In order to achieve high energy dissipation, we need to arrange more steps, about 50-130 steps, and the amount of construction in the actual project is more. This kind of project is not suitable for the use of staircase energy dissipator.
10. research on safety problems such as cavitation, scouring and vibration of staircase energy dissipator in hydraulic tunnel. The time average pressure and pulsating pressure are the key factors to cause the above safety problems. In this paper, the time average pressure and pulsating pressure of four main influencing factors of the single wide flow, the flush number, the bottom slope and the staircase height, and the pulsating pressure Strength, pulsating pressure maximum and minimum instantaneous value, pulsating power spectrum and other hydraulic parameters are studied. The results show that the maximum value of the maximum value is p/h=3.5, the maximum instantaneous pressure is p/h=9.5. first step the maximum negative pressure p/h=-0.8, the maximum negative pressure is p/h =-0.6 along the step ladder, and the pulsating pressure in the region along the ladder is the minimum transient pressure. At the time value of p/h=-2.5m., the maximum positive pressure and the maximum negative pressure of the ladder vertical face are all within the safe bearing capacity of the concrete under the condition of full aeration of the water. The strong vibration of the working.
In the actual hydraulic tunnel, the staircase staircase energy dissipation is designed, the staircase shape and the ladder layout should take into consideration the flow state, the aeration characteristic and the energy dissipation effect. The unilateral pursuit of high energy dissipation will increase the unnecessary cost. If the hydraulic tunnel has sufficient space, the water flow should be formed into the sliding flow, and the middle and downstream staircase flows are fully entered. The aeration zone, at the same time, controls the energy dissipation rate of the outlet of the hydraulic tunnel, so that it does not destroy the downstream river bed and the bank slope when connecting with the downstream flow. If the hydraulic tunnel space is restricted, the energy dissipation effect and the flow pattern are considered first, and the flow of the flow can be evenly mixed.
【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TV672.1;TV135

【参考文献】