拦污栅栅条流场特征和共振分析

更新时间:2023-05-30 12:49:45 阅读: 评论:0

楼月汤蓉摘要
孕妇能吃酒酿吗拦污栅是布置在水电站、泵站和船闸输水廊道等水工建筑物进水口处不可或缺的重要设施,用以截留水流中所挟带的漂浮物和悬浮物,保护发电机组、闸门、管道等相关设施不受损害。拦污栅运行条件复杂,例如抽水蓄能电站拦污栅需要承受双向水流作用,不同运行工况下的水流方向频繁变化导致的拦污栅前流速较高、流速分布不均匀、栅面与来流冲角较大等问题都使拦污栅受流激振动而导致的破坏几率增加。拦污栅如果发生破坏,不仅维修困难,而且会影响电站运行效率。更严重的,其一旦发生松动脱落并被吸入水轮机,会导致水轮机毁坏,电站将停产检修,将产生巨大的经济损失。因此,拦污栅的科学设计、合理装配、安全使用对电站的安全稳定运行,提高水利经济与社会效益意义重大。马蹄怎么做好吃
以往针对拦污栅的研究,大多从优化结构体型、提高承载力的角度出发,而对拦污栅受湍流作用导致振动破坏的研究较少。拦污栅的流激振动问题是典型的流固耦合问题,针对该问题的模拟,由于涉及水流条件、边界条件以及拦污栅自身结构动力特性等方面特点,其建模与计算一直是工程研究中的一大难点。本文基于前人研究经验,从栅条截面形状这一重要影响因素出发,采用数值模拟与理论分析相结合的方法对圆形、正方形、长矩形、前缘半圆矩形以及两缘半圆矩形五种截面栅条的受力特征、压力分布、流速分布及涡脱频率进行研究,研究内容及所得结论如下:
(1)总结拦污栅破坏的原因,并从振动发生机理、振动破坏特征与振动研究方法三方面对拦污栅流激振动破坏这一问题的研究现状进行了回顾。
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(2)为准确模拟栅条周围流场结构并精确捕捉栅条周围漩涡脱落,本文选择k-ωSST湍流模型进行模拟,模型离散格式在时间上采用一阶隐式格式,空间上对流项采用三阶QUICK格式、扩散项采用二阶CDS格式,选取PISO算法进行压强速度解耦,使用混合网格划分计算域,针对拦污栅工程运行中的两个典型工况,即入口流速分别为
1m/s(Re=2×104)与3m/s(Re=6×104)进行数值建模。
(3)分析了不同形状截面栅条在不同流速作用下的流速场分布结果,分别从轴线流速分布、回流区形态及断面流速分布三方面对比讨论各栅条流速场特征。结果表明:两缘半圆矩形截面栅条栅后流场流速分布最为均匀,此截面形式的拦污栅在进水口处可减少或避免吸气漩涡的产生,保护发电机组,在出水口处可有效避免局部冲刷等不利因素,可减少过栅后不良流态造成的相关危害。
(4)从流场压强与壁面压强两方面入手,分析了不同形状截面栅条在不同来流流速下的压力场分布结果。由阻力系数C d最大值计算栅条壁面合力,简化栅条结构及受力,计算栅条最大挠度ωmax,对栅条的抗弯承载力进行校核。结果表明:圆截面与正方形截面栅条不满足工程所需的刚度条件要求,其余三种矩形截面栅条满足刚度条件,并且拥有较大的富裕度,即其刚度条件可以承受更大流速的水流过栅。
(5)统计栅条附近采样点瞬时速度值,通过计算得到栅条不同部位流场漩涡脱落频率,并与栅条在
水中的固有频率进行比较,计算各形状栅条发生共振的安全阈值。结果表明:两缘半圆矩形截面栅条拥有最大的避免共振的安全阈值。随着过栅流速的增加,此形状栅条最不容易产生共振。
本文所得结果不仅对优化设计拦污栅、合理选择其运行条件、采取措施避免拦污栅因流激振动而遭受破坏等工程实践具有重要指导价值,而且可对类似流固耦合问题的研究提供借鉴。
关键词:拦污栅栅条;数值模拟;刚度校核;流场特征;漩涡脱落;共振频率
- II -
The Flow Field Characteristics and Resonance Analysis of Trash-rack Bars
Abstract
侍御The trash-rack is an indispensable and important facility in the water inlet of hydraulic structures such as hydro-power station, pumping station and ship lock, and it is ud to intercept the floating objects and suspended objects carried in the flow and protect the generator t, gate, pipeline and other related facilities from damage.The operation conditions of the trash-rack are extremely complicated. For example, trash rack need to withstand two-way water in pumped storage power station,and the problems of high flow velocity, uneven flow velocity distribution and large impact angl
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e of trash-rack surface caud by the frequent change of flow direction under different operating conditions increa the flow induced vibration damage. If the trash-rack is damaged, it will not only be difficult to maintain, but also affect the efficiency of power station operation. More riously, once it loons and is sucked into the turbine, it will cau the turbine to be destroyed, and the power station will be shut down for maintenance, resulting in huge economic loss. Therefore, the scientific design, reasonable asmbly, and safe u of trash-rack are of great significance to the safe and stable operation of power stations, and to improve the economic and social benefits of power stations.
In the past, most of the rearches on trash-rack were from the perspective of optimizing the structure and improving the bearing capacity. However, there have been few studies on the vibration damage of trash-rack caud by turbulence. The flow-induced vibration problem of the trash-rack is a typical fluid-structure interaction problem. For the simulation of this problem, due to the characteristics of water flow conditions, boundary conditions and dynamic characteristics of the trash-rack itlf, its numerical modeling and accurate simulation have always been a major difficulty in engineering rearch.In this paper, bad on previous rearch experience, starting from the important influence factor of the cross-ctional shape of the grid-bar, combined numerical simulatio
n and theoretical analysis to study the stress characteristics, pressure distribution, flow velocity distribution and vortex off frequency of five kinds of ction grids of circle, square, long rectangle, leading-edge micircular rectangle and two-edge micircular rectangles. The rearch content and conclusions are as follows:
(1)Summarize the caus of trash rack damage, and review the rearch status of flow-induced vibration damage for trash-rack from three aspects: vibration generation mechanism, vibration damage characteristics and vibration rearch methods.
(2)In order to accurately simulate the flow field structure around the grid bars and accurately capture the vortex shedding around the grid-bars, this paper lects the k-ωSST turbulence model for simulation. The discrete format of the model adopts the first-order implicit format in time, the spatial convection term adopts the third-order QUICK format, and the diffusion term adopts the cond-order CDS format. The PISO algorithm is ud for pressure velocity decoupling, finally, the calculation domain is divided using a hybrid grid. Aiming at two typical working conditions in the operation of trash rack project, the inlet velocity is 1m/s(Re=2×104) and 3m/s(Re=2×104), a numerical model is established.
(3)The velocity field distribution results of grid bars with different ctions under different velocity are analyzed, and the velocity field characteristics of each grid-bar are compared and discusd from the three aspects of axial velocity distribution, reflux zone shape and cross-ctional velocity distribution. The results show that the flow field velocity distribution is the most uniform after the grid-bar with two edges mi-circular rectangular ction. The type of trash-rack with this ction can reduce or avoid the generation of suction vortex at the water inlet, protect the generator t, effectively avoid local scouring and other adver factors at the water outlet, and reduce the related hazards caud by the bad flow pattern after the trash-rack .
(4)Starting from the two aspects of flow field pressure and wall pressure, the pressure field distribution results of grid bars with different cross-ctions under different Reynolds numbers are analyzed. This paper calculates the total force of the grid bars’wall with the maximum value of the drag coefficient C d, and simplify the structure and stress of the grid bars, calculate the maximum deflection ωmax of the grid bars, finally check the bending capacity of the grid bars. The results show that the grid bars with circular ction and square ction do not meet the stiffness conditions required by the project. The remaining three grid bars with long rectangular ction, leading-edge micircular rectangle, and two-edge micircular rectangle meet the stiffness conditions and have g
reater affluence, that is, their stiffness conditions can withstand higher velocity water flow Cross fence.
(5)This paper monitors the instantaneous velocity value of the sampling point near the grid bars, calculates the vortex shedding frequency of the flow field in different parts from the grid bars, and compares it with the natural frequency of the grid bars in the water to calculate the safety threshold for the resonance of grid bars. The results show that the grid bars with two-edge mi-circular rectangular ction has the largest safety threshold for avoiding resonance. As the flow rate increas, the grid bars with this ction are the least prone to resonance.
- IV -qq消息提示音
The results obtained in this paper not only have important guiding value for engineering practice such as trash-rack’s design , rational lection of operating conditions, and measures to avoid flow-induced vibration damage to the trash-rack, but also can provide reference for the study of similar fluid-structure interaction problems.
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Key Words:Trash-Rack Bars; Numerical Simulation; Stiffness check; Flow Field Characteristics; Vortex Shedding; Resonance Frequency

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