THREE-DIMENSIONAL NUMERICAL SIMULATION OF AERATED FLOWS DOWNSTREAM SUDDEN FALL AERATOR EXPANSION-IN A TUNNEL

Air entrainment is known to be one of efficient and inexpensive methods to prevent cavitation damages in hydropower projects.The shape of sudden expansion-fall is used as a common device for mitigating cavitation erosions.The complex flow patterns with cavitation are numerically simulated by using the realizable k-εturbulence model and the air-water mixture model.The calculated results are compared well with the experimental results as well as those obtained with the k-εturbulence model with the Volume Of Fluid(VOF)Model.The calculated results agree well with the experimental data for the aeration cavity and wall pressure.Moreover,the air concentration near sidewall is simulated by a mixture model.It is found that the mixture turbulence model is superior to the VOF turbulence model.     

扩散段长度对侧式进/出水口水力特性的影响

以某上水库无调整段侧式进/出水口为研究对象,采用雷诺应力湍流模型探究了扩散段长度对进/出水口水力特性的影响规律,并从水力学的角度给出了扩散段长度建议值。结果表明：扩散段长度对侧式进/出水口水流运动存在显著影响,扩散段不宜过长或过短;对于进/出水口沿程流速分布,只有在抽水工况下扩散段长度才会对其产生影响,发电工况下基本不存在影响;对于水头损失、各孔口流量配比等其他水力指标,扩散段长度在双向过流时均会对其产生较大影响,随着扩散段长度的增加,各水力指标均先变好再变差;对于无调整段侧式进/出水口体型,当扩散段长度为隧洞直径的5.7～6.0倍时,各水力指标满足规范要求;当扩散段长度为隧洞直径的5.8倍时,进/出水口水力特性得到较大改善,且具有较好的水流流态。     

抽水蓄能电站侧式进/出水口隔墩布置对水力特性的影响

运用标准k-ε湍流模型和VOF两相流模型,对抽水蓄能电站侧式进/出水口、输水管道和部分上库进行了数值计算,分析了死水位条件下抽水和发电工况的进/出水口隔墩位置对进/出水口流速分布、流道分流系数、水头损失、墩头附近流速分布等水力特性的影响。结果表明:中隔墩后移对发电工况下各流道流速分布、分流系数、进/出口的水头损失几乎无影响;中隔墩后移可改善抽水工况下中隔墩两侧流道的过流流速均匀性和各流道流量分配的均匀性,降低进/出水口的水头损失,但中隔墩后移距离超过进/出水口扩散段起始断面宽度的0.3倍时,改善效果不明显;中隔墩后移进/出水口扩散段起始断面宽度的0.44～0.52倍,边隔墩后移进/出水口扩散段起始断面宽度的0.1倍,可实现墩头附近局部流速的相对均匀化;中隔墩后移扩散段起始断面宽度的0.5倍,边隔墩后移扩散段起始断面宽度的0.1倍,可实现抽水蓄能电站进/出水口水力特性的最优化目标。     

A NUMERICAL METHOD FOR CALCULATING THE EFFECTS OF INLET FLOW ON HYDRODYNAMIC CHARACTERISTICS OF A HYDROFOIL-STRUT-POD CONFIGURATION

A numerical method based on the doublet distribution for calculating theeffects of inlet flow on hydrodynamic characteristics of a hydrofoil-strut-pod configurationunder the linearized free water surface condition is presented in this paper.Inlet flow con-dition is represented by a control section S,in the inlet tube on which the axial velocity is u-niform and determined by a given flowrate.The numerical results for some typical casesare compared with corresponding experimental data.It is found that good agreement be-tween computational and experimental results can be achieved.This numerical methodmay be applied to the prediction of foilborne performance characteristics of a waterjet pro-pelled hydrofoil craft and to optimization of integrated hydrofoil waterjet propulsion sys-tem.     

侧式进/出水口顶板扩张角对拦污栅断面流速分布影响规律研究

抽水蓄能电站侧式进/出水口双向过流,其顶板扩张角的大小将直接影响拦污栅断面流速分布是否均匀,甚至出现反向流速。抽水蓄能电站设计规范将3°~5°作为侧式进/出水口顶板扩张角的推荐范围,其依据是矩形渐扩管阻力系数最小的扩张角度,但侧式进/出水口体型较之复杂很多,因此有必要进一步探讨。本文以某侧式进/出水口体型为研究对象,采用数值模拟方法,研究了11种角度的顶板扩张角对出流工况和进流工况拦污栅断面流速分布的影响。结果表明：在出流工况下,随着顶板扩张角的增大,中孔拦污栅断面的主流位置由居中部逐渐向底部降低,断面流速分布由上下基本对称趋于底部大上部小的上下不对称,当顶板扩张角较大时中孔拦污栅断面上部出现反向流速;随着顶板扩张角的增大,边孔拦污栅断面流速分布由基本均匀逐渐变为底部大上部小的不均匀分布;随着顶板扩张角的增大,中、边孔孔口流速不均匀系数均逐渐增大,但中孔拦污栅断面流速分布受顶板扩张角影响更大。在进流工况下,随着顶板扩张角的增大,中、边孔拦污栅断面流速分布及孔口流速不均匀系数均无明显影响。研究成果可为优化侧式进/出水口设计提供指导。     

荒沟抽水蓄能电站上池侧式进口和出口水力学试验研究

影响抽水蓄能电站进、出水口水流特性的主要因素之一是进口水流的波涡问题，故侧式进、出水口上方常采用矩形或百叶窗式斜染进行防涡．但就荒沟抽水蓄能电站上池而言，采用这种消涡措施，经试验测得进水目前平均流速达1．60m／s左右，在各级发电工况运行时，防涡梁上方均产生吸气漩涡．依此对原防涡方案进行了修改和研究，提出了阶梯立式防涡梁防涡和消涡方案，取得了较好的防涡和消涡效果，从而为防涡工程提供了一种新的措施．     

NUMERICAL SIMULATION OF THE ENERGY DISSIPATION CHARACTERISTICS IN STILLING BASIN OF MULTI-HORIZONTAL SUBMERGED JETS

3-D numerical simulation was carried out for the water flow in a stilling basin with multi-horizontal submerged jets by using two different turbulence models, namely, the VOF RNG k - ? and Mixture RNG k - ? turbulence models. The calculated water depth, velocity profile and pressure distribution are in good agreement with the data obtained in experiments. It indicates that the numerical simulation can effectively be used to study the water flow movement and the energy dissipation mechanism. The numerical simulation results show that the turbulent kinetic energy distribution obtained by using the Mixture turbulence model covers a region about 18% larger than that calculated by using the VOF turbulence model, and is in better agreement with the actual situation. Furthermore, the Mixture turbulence model is better than the VOF turbulence model in calculating the air entrainment.     

抽水蓄能电站进/出水口体型优化数值模拟

利用三维紊流数学模型,对某抽水蓄能电站上水库进/出水口原方案及其优化方案抽水和发电工况进行数值模拟,分析了进/出水口段的水头损失、进/出水口段的流态和流速分布等。原方案在抽水工况下,存在扩散段及调整段顶盖板下部产生水流分离区、拦污栅断面有反向流速、各孔口流速不均匀系数偏大等不利水力学现象。考虑以上不利因素,需对原方案进行优化。优化方案计算结果表明,在扩散段和防涡梁段之间增加调整段、压低扩散段盖板扩散角以及增加扩散段长度等措施均能改善水流流态。     

Theoretical and numerical study of hydraulic characteristics of orifice energy dissipator

Different factors affecting the efficiency of the orifice energy dissipator were investigated based on a series of theoretical analyses and numerical simulations.The main factors investigated by dimension analysis were identified,including the Reynolds number(Re),the ratio of the orifice diameter to the inner diameter of the pipe(d/D),and the ratio of distances between orifices to the inner diameter of the pipe(L/D).Then,numerical simulations were conducted with a k-ε two-equation turbulence model.The calculation results show the following:Hydraulic characteristics change dramatically as flow passes through the orifice,with abruptly increasing velocity and turbulent energy,and decreasing pressure.The turbulent energy appears to be low in the middle and high near the pipe wall.For the energy dissipation setup with only one orifice,when Re is smaller than 105,the orifice energy dissipation coefficient K increases rapidly with the increase of Re.When Re is larger than 105,K gradually stabilizes.As d/D increases,K and the length of the recirculation region L1 show similar variation patterns,which inversely vary with d/D.The function curves can be approximated as straight lines.For the energy dissipation model with two orifices,because of different incoming flows at different orifices,the energy dissipation coefficient of the second orifice(K2)is smaller than that of the first.If L/D is less than 5,the K value of the L/D model,depending on the variation of K2,increases with the spacing between two orifices L,and an orifice cannot fulfill its energy dissipation function.If L/D is greater than 5,K2 tends to be steady; thus,the K value of the L/D model gradually stabilizes.Then,the flow fully develops,and L has almost no impact on the value of K.     

某抽水蓄能电站下库侧式进/出水口数值模拟

抽水蓄能电站进/出水口有进流和出流两种工况,进/出水口水流呈双向流动,水力条件较复杂,对水流流态要求较高。因此,为观测各工况水流流态和水头损失大小,进一步完善进/出水口的结构布置和尺寸,对下库进/出水口进行了数值模拟计算。根据隧洞中水流的运动为有压流这一特点,建立了隧洞压力驱动三维水动力模型,考虑了进/出水口上游一定长度隧洞在内的三维空间计算域,采用k-ε紊流模型,通过对隧洞内压力流的数值模拟,分析研究了各工况下流道分离比、流速、流态及水头损失等水力特性。研究表明:将中边孔导流隔墩尾部位置进行调整能有效改善中、边孔分流比,流速不均匀系数也有所改善,水头损失无明显变化。     

输水隧洞坡角对侧式进/出水口水力特性影响研究

抽水蓄能电站侧式进/出水口具有双向过流的特点,进/出水口自身体型参数对其水力特性具有很大的影响,但连接的输水隧洞布置型式也同样会影响进/出水口水力特性,若输水隧洞布置不恰当,将可能导致进/出水口出现不利的水力特性。利用RSM紊流模型,以某侧式进/出水口为研究对象,在进/出水口体型不变的前提下,研究出流工况不同隧洞坡角对进/出水口内部流态、拦污栅断面流速不均匀系数、水头损失系数及流量分配等水力特性的影响。结果表明,当隧洞坡角等于扩散段垂向扩散角时,进/出水口内部流态较好,反向流速区的沿程范围、拦污栅断面流速不均匀系数及水头损失系数均最小。因此,当进/出水口扩散段垂向扩散角不大且各隧洞坡角均满足地形、地质条件的情况下,隧洞坡角等于扩散段垂向扩散角时,可获得较优的水力特性。