基于环形旋转射流的预掺混扩散器水力特性试验研究

预掺混扩散器在污水出流前掺入其周围的水进行预先稀释,可增强初始稀释度,减小混合区范围。为进一步提高扩散器的稀释水平,本文提出了一种基于环形旋转射流的新型预掺混扩散器,在进流方式以及排放形式方面另辟蹊径,并系统地研究了该扩散器射流的温度场、流场和内部压力分布。研究结果表明:该预掺混扩散器稀释性能稳定,流量放大倍比约为2.5,排口处温升极值可降低约50%,1.2倍排口直径处可降低约80%;排口后环形旋转射流无速度核心区,存在内掺混机制,极值温升及流速沿喷距呈幂函数衰减规律,具有更短的射程和更强的掺混稀释能力,对迅速缩减污染带十分有利;水头损失系数较小,约为2.4。采用该预掺混扩散器,可在离岸较近的浅水区域获得较常规扩散器深排的稀释效果,进而缩短排污输水管道、降低工程投资。     

弱环境流速水域内陆核电厂液态流出物排放设计优化研究

理论和实践经验均表明,内陆核电厂采用多孔扩散器有利于加快近排放口区域液态流出物的掺混稀释。基于美国环保署推荐的近区模拟工具——CORMIX专家系统,对低环境流速水文条件下的内陆核电厂的多孔扩散器开展了研究。分析表明:对于近岸布置的多孔扩散器,在低环境流速、相对较强射流以及水深较深条件下,(1)扩散器主管长度Ln与排放口下游断面的最小相对稀释比例H呈正相关,喷口直径D与H呈负相关,喷口水深HD与H呈正相关;在排热量相同的情况下,流量Q与H呈正相关。(2)对于排放口下游1 000 m断面处的最小相对稀释比例H1 000 m,各几何参数灵敏度由高到低排序为,喷口直径D、喷口数量n、主管长度Ln。研究结论可供内陆核电厂液态流出物排放工程的设计及优化参考。     

Mixing characteristics of 45° inclined duckbill dense jets in co-flowing currents

The use of duckbill valves in submerged outfalls for dense effluents is now prevalent to prevent the intrusion of ambient water into the outfall pipe during periods of low production of the facility. In the present study, an experimental investigation was conducted using the technique of Planar Laser Induced Fluorescence (PLIF) to examine the mixing characteristics of 45° inclined dense jets from a duckbill shape nozzle in co-flowing currents. The measured characteristics included the jet trajectory, concentration decay, centreline peak dilution and cross-sectional concentration distribution. The Froude number ranged from 10 to 25, and the nominal Froude number from 0.2 to 3.0. Two mounting orientations of the duckbill nozzle, namely vertical and horizontal, were also investigated. The experimental results showed that two regimes, namely dense-jet- and co-flow-dominated, can be clearly observed. When the co-flow velocity increases, the centreline peak height and dilution of the inclined dense jet decrease. Comparing to the available results in the literature for inclined circular dense jets, the centreline peak dilution for inclined duckbill dense jets is generally higher. In other words, the installation of the duckbill valve also contributes to the mixing of the dense effluent with surrounding ambient waters, in addition to preventing the ambient intrusion. With respect to the mounting orientation, the horizontal induces a relatively higher dilution but also a larger centreline peak height. Thus, the horizontal orientation would be preferable when the cover water depth is sufficient, while the vertical orientation can be considered in shallow waters for full submergence.     

基于环型射流抽吸原理的新型预掺混扩散器稀释特性初探

预掺混扩散器区别于常规扩散器,在污水自扩散器出流前提前掺入环境水进行预稀释,可有效提高污水射流初始稀释度、减小混合区范围。本文通过调研分析,总结归纳了管壁开孔式、套管式及终端式这三类已有预掺混扩散器的工作原理,提出制约预掺混扩散器应用推广的主要因素是稀释效果欠佳、水头损失过大。在此基础上,提出基于环形射流抽吸原理的预掺混扩散器,并采用模型试验与三维数值模拟方法初步研究了污水径向进流与切向进流两种结构型式扩散器的流量放大倍比及紊动掺混效果。研究结果表明,这两类进流方式的预掺混扩散器均可有效实现环境水对污水的提前掺混,其中切向径流效果更优。     

Two-phase velocity measurement in a particle-laden jet

A horizontally discharging jet laden with solid sediment particles is investigated experimentally. The submerged jet discharges water with an initially horizontal direction into stagnant water of the same density but the presence of sediment particles produces jet effluent having a combined density greater than that of the ambient water. A modified particle-imaging velocimetry (PIV) technique is applied to estimate the velocity fields of the solid particle phase and the jet fluid liquid phase. Phase separation is achieved optically between the scattered light signals from the particles and the laser-induced fluorescence signal from the jet fluid dozed with a fluorescent dye. It is found that initial sediment concentrations below 0.1% volume fraction do not cause significant changes to the global properties of the jet flow. In jets of higher initial sediment concentrations, settling of sand particles are observed to drag the jet to spread with a downward-bending mean trajectory. Intensive particle–flow interaction is also observed in jets of high sediment concentrations.     

PARAMETRIC STUDY ON THE THRUST OF BUBBLY WATER RAMJET WITH A CONVERGING-DIVERGING NOZZLE

To predict the thrust of bubbly water ramjet with a converging-diverging nozzle, the physical processes occurring in the diffuser, mixing chamber and nozzle were analyzed. The mathematical models were constructed separately under the restrictions of certain assumptions. The bubbly nozzle flow was examined using a two-fluid model and accomplished by specifying the water velocity distribution in the nozzle. The numerical analysis of flow field in the nozzle shows that the Mach number at the throat is 1.009, near unity, and supersonic bubble flow appears behind the throat. There is greater thrust produced by bubbly water ramjet, compared with single-phase air ramjets. Subsequently, the influences of vessel velocity, air mass flow rate, inlet area A_m, area ratio (i.e., mixing chamber to inlet area A_m/A_i), and initial bubble radius on the thrust were emphatically investigated. Results indicate that the thrust increases with the increase of air mass flow rate, inlet area and the area ratio, and the decrease of initial bubble radius. However, the thrust weakly depends on the vessel velocity. These analytical and numerical results are useful for further investigation of bubbly water ramjet engine.     

NUMERICAL SIMULATION OF HORIZONTAL BUOYANT WALL JET

This article applies the realizable k-ε model to simulate the buoyant wall jet and gives the results of cling length,centerline trajectory and temperature dilutions at certain sections.The comparison between the numerical results and Sharp's experimental data indicates that the model is effective in estimating velocity distribution and temperature dilutions.The velocity profiles at the cental plane and z-plane both show a strong similarity at certain distance from the nozzle,and the distributions of velocity and temperature dilutions also exhibit a similarity along the axial direction at centerline in the near-field.Based on the results,the article gives the corresponding relationships between the distance and the dilutions of velocity and temperature,which is useful in predicting the behavior of the wall buoyant jet.     

THEORETICAL AND EXPERIMENTAL STUDY ON THE CONICAL SWIRLING WATER JET FLOW

This paper is concerned with theoretical and experimental study on theconical swirling water jet flow.Based upon the theoretical analysis,the experiment on thestructural characteristics of swirling water jet flow including the velocity and pressure dis-tribution laws,on which the parameters of the jet,nozzle and directional blades havemore or less influence,was carried out in CSSRC by using a 3-D LDV in order to optimizea new high-efficiency jet instead of swirling drilling bit for rock-breaking and continuouslydrilling,and to meet the demand of radial horizontal drilling technology.Meanwhile basedon the experimental results,the numerical simulation was conducted for the conicalswirling water jet in the immersed well-bottom flow by solving the RANS equations in the3-D body-fitted coordinate system with the k-ε turbulence model.The numerical resultsare consistent with the experimental data,and lead to some conclusions which are impor-tant for applying the conical swirling water jet to the petroleum drill     

Dilution characteristics of dual buoyant jets in wavy cross-flow environment

Due to the difference in density between the discharge effluent and coastal water, partially treated wastewater is often discharged into the marine environment as a buoyant jet via submarine outfalls with multiport diffusers. The dilution characteristics of effluent discharge (dual buoyant jets) in a wavy cross-flow environment were studied in a laboratory. The planar laser-induced fluorescence technique was used to obtain the concentration data of the jets. The effects of different environmental variables on the diffusion and dilution characteristics of the jets were examined through physical experiments, dimensional analysis, and empirical formulations. It was found that the dilution process of the dual jets could be divided into two components: the original jet component and the effluent cloud component. The jet-to-current velocity ratio was the main parameter affecting the concentration levels of the effluent cloud. The merging of the two jets increased the jet concentration in the flow field. When the jets traveled further downstream, the axial dilution increased gradually and then increased significantly along the axis. Under the effects of strong waves, the concentration contours branched into two peaks, and the mean dilution became more significant than under the effects of weak waves. Therefore, the dilution of the effluent discharge was expected to be significant under strong wave effects because the hydrodynamic force increased. A dilution equation was derived to improve our understanding of the dilution process of buoyant jets in a wavy cross-flow environment. This equation was used to determine the influences of the jet-to-current velocity ratio, wave-to-current velocity ratio, and Strouhal number on the minimum jet dilution. It revealed that the wave and buoyancy effects in effluent discharges were significant.     

STABILITY AND MIXING CHARACTER FOR BUOYANT JETS IN QUIESCENT SHALLOW WATER

BRIEFINTRODUCTIONOFTHEPAPER:Inthe firstpart,thecharactersforthe3Dthermalbuoy antjetsintheflowingenvironmentareanalyzed experimentally.UsingtheMicroADVandtem peraturemeasuringsystem,thevelocityfieldand temperaturefieldoftheheatedbuoyantjetsatdif ferentcross to jetvelocityratiosaremeasured.Thetestdatarevealedthecharacteristicsofthose meanflowparametersandturbulentflowparame tersaregaveout.Furthermore,theexperimental runsarenumericallysimulatedusingthebuoyancy extendedkεturbulencemo…     

Mixing of inclined dense jets in stationary ambient

This paper reports results of a comprehensive experimental investigation of inclined round dense jets in an otherwise stagnant fluid. The tracer concentration field is measured for six jet discharge angles: θ_o = (15°, 30°, 38°, 45°, 52°, & 60°) and jet densimetric Froude number of Fr = 10–40 using the planar laser-induced fluorescence (LIF) technique; selected jet velocity measurements are made using Particle Image Velocimetry (PIV). The detailed jet mixing characteristics and turbulence properties are presented. The direct velocity measurement reveals that the mixing is jet-like until the maximum rise. Empirical correlations for the maximum jet rise height, jet dilution at maximum rise, and impact dilution are presented. Both the time-mean concentration and intermittency show that the upper jet edge spreading is similar to a positively buoyant jet; at the lower edge the buoyant instability induces significant detrainment and mass outflux for θ_o > 15°. The dimensionless maximum rise height Z_max/(FrD) is independent of source conditions for Fr ≥ 25, and varies from 0.44 for θ_o = 15° to 2.08 for θ_o = 60°. Dilution measurements at terminal rise show the difference in dilution is small for θ_o = 38°–60° and the asymptotic dilution constant is S_t/Fr = 0.45. The impact dilution S_i is also not sensitive to jet angle for θ_o = 38°–60° and can be expressed as S_i/Fr = 1.06 for Fr ≥ 20.The Lagrangian jet model VISJET is used to interpret the experimental results. A detailed derivation for a general formulation of the entrainment coefficient is presented. Despite the observed detrainment, the trajectory and dilution are reasonably predicted; the maximum jet rise is generally under-predicted by 10–15% and associated dilution by 30%. However, the predicted variation of jet behavior with discharge angle is in good agreement with measurements. The experimental data is also compared with predictions of alternative models that employ an ad hoc entrainment hypothesis.     

双射流流动结构实验研究

应用PIV实验方法对由直射流和同心的环状旋转射流组成的双射流流场进行了测量，并分析研究了流场的速度和旋度变化规律。分析表明，双射流等速核长度较小，仪约为5倍喷距；随喷距的增加其多股射流特性逐渐减弱，其主要原因为直射流和旋转射流在交界面上很强的剪切作用；旋转射流的径向发展因受直射流吸附作用的影响而减小，相应直射流速度在喷嘴轴线上的衰减则增加。在4-6倍喷距间的旋转射流速度突然下降和相应位置处旋度场的涡环都显示该处可能存在较强的空化现象，而大大提升双射流的能力。     

孟加拉湾巴瑞萨河口温排放初始稀释特性研究

为提高温排放的初始稀释度、减小排口近区超标区域,扩散器常被用于电厂排海工程。本文采用CORMIX经验模型与Realizable k-ε紊流模型相结合的方法,开展了孟加拉湾河口水域燃煤电厂排水扩散器的参数优化及温排水稀释特性研究。首先分析了扩散器长度、出流角度、出流流速等参数对初始稀释的影响,并对扩散器型式进行了比选,提出潮汐水域采用交错型扩散器有利于增大近区稀释度。针对推荐扩散器,研究依据准恒定假设,模拟了涨潮、高平、落潮、低平四个特征潮态的温排水稀释扩散过程。结果表明:不同潮态的温度场空间结构、温升分布及稀释效果具有显著差异,低平潮对温排水掺混稀释最为不利;涨潮与落潮时顺流向与逆流向的喷口射流结构也不尽相同,顺流向射流更加细长。研究成果可为电厂排放口工程设计与环境影响评价提供技术支撑,也可为浅水型海域扩散器选型提供参考。     

斜向进水消力井水力特性模拟研究

水利水电工程中的泄水建筑物出口往往正冲河道,圆形消力井可以很好地适应山区峡谷地形条件的变化,使下泄水流平顺归河。针对一定纵坡条件下,尾水出口与泄槽轴线呈非对称正交的圆形消力井内复杂的水力特性问题,采用有限域数值模拟计算的方法对比验证并补充了物理模型试验成果,进一步开展了沿空间射流方向的相关水力要素机理分析。研究表明:消力井内水流流态依次呈平面横向紊动扩散自由射流、主流动力自相似淹没射流和冲击射流、近壁面附着扩散旋滚水跃3个临界雷诺数分区演变过程;沿程最大流速变化符合试验半经验公式拟合规律且近似呈平面扩散分布;水体压强结构特征可分解为水平轴对称及竖直变幅下的叠加分布。     

内陆核电液态流出物排放口型式优化研究

液态流出物排放方式优化是内陆核电重点关注的问题之一,本文针对国内某内陆核电厂址液态流出物排放口型式进行优化研究,以提高初始稀释度,降低液态流出物排放对环境水体的影响。选取CORMIX软件作为优化工具,采用河道实体模型试验近区稀释度测量结果对CORMIX断面概化合理性进行了验证分析,在此基础上对单喷口和多喷口排放的出流水平方位角、垂向仰角、出流流速,多喷口间距等参数进行了优化,提出了各参数适宜的取值范围。研究表明,本厂址水深有限,采用水平深层排放加强垂向掺混能获得更好稀释效果,同等环境流速、水深,采用相同的排放仰角、排放流速和排放位置等设计参数,多喷口排放型式稀释效果优于单喷口。本文结果可供工程设计和相关研究参考。     

不同动力环境下孔间距对双孔射流特性的影响

为研究孔间距对双孔射流运动和稀释特性的影响,采用粒子图像测速技术(PIV)和激光诱导荧光技术(PLIF)分别对静水、横流和波浪环境下双孔射流的速度场和浓度场进行测量,对比分析了孔间距为5倍、10倍和15倍射流孔直径时双孔射流的轴向速度、横断面垂向速度、轨迹线及浓度场分布情况。结果表明:在静水环境下,孔间距较小时双孔射流的轴向速度衰减较单孔射流慢,随着孔间距的增大双孔射流轴向速度衰减的程度逐渐趋近于单孔射流。在横流环境下,随着孔间距的增大,前方射流对后方射流的遮掩作用不断减小,而后方对前方射流的卷吸作用也有所减弱,导致前方射流弯曲程度的增大和后方射流上升高度的降低。在波浪环境下,孔间距较小时,两孔中间存在一个独立的高浓度区;孔间距增大后,浓度等值线逐渐呈"凸"形分布。为降低双孔射流相互作用对射流初始稀释的影响,建议在波浪和横流环境下双孔射流的孔间距不宜小于射流孔直径的10倍。     

竖管式扩散器排放近区数值模拟研究

结合我国排放口设计的发展方向，通过数值模拟方法研究了竖管式多孔扩散器排放近区的稀释特性和数值预报模型。针对前人二维当量长孔浮射流理论不能考虑扩散器附近单个浮射流的混合特征的不足之处，提出了多孔浮射流混合前后的耦合模拟方法，建立了竖管式扩散器排放近区单侧混合的数值模型，并通过模型试验加以验证。结果表明，数值计算成果与模型试验成果基本一致，可以直接用于竖管式扩散器表层初始稀释度的预报。     

多孔射流扩散器在宽浅型江河中排放特性研究

多孔射流扩散器排放城市污水是充分利用天然水体环境容量和自净能力的有效途径，本文以水槽试验资料为基础，分析了流动水体中多孔射流扩散器排污下游流场和浓度场的主要影响参数，根据多孔射流与环境水体的掺混稀释特性，采用虚拟扰动源的处理方法，给出了描述扩散器排放下游流速与浓度的分布公式，该公布公式的计算结果与实测值吻合较好。     

Numerical simulation of the abrasive supercritical carbon dioxide jet: The flow field and the influencing factors

The supercritical carbon dioxide(SC-CO_2) jet can break rocks at higher penetration rates and lower threshold pressures than the water jet. The abrasive SC-CO_2 jet, formed by adding solid particles into the SC-CO_2 jet, is expected to achieve higher operation efficiency in eroding hard rocks and cutting metals. With the computational fluid dynamics numerical simulation method, the characteristics of the flow field of the abrasive SC-CO_2 jet are analyzed, as well as the main influencing factors. Results show that the two-phase axial velocities of the abrasive SC-CO_2 jet is much higher than those of the abrasive water jet, when the pressure difference across the jet nozzle is held constant at 20 MPa, the optimal standoff distance for the largest particle impact velocity is approximately 5 times of the jet nozzle diameter; the fluid temperature and the volume concentration of the abrasive particles have modest influences on the two-phase velocities, the ambient pressure has a negligible influence when the pressure difference is held constant. Therefore the abrasive SC-CO_2 jet is expected to assure more effective erosion and cutting performance. This work can provide guidance for subsequent lab experiments and promote practical applications.     

利用数字图像处理技术测量浓度场的实验研究

利用数字图像处理技术是当前研究环境污染物扩散机理的重要手段。该文通过水槽实验,分析了污染物图像的灰度与污染物的浓度、光源的距离以及排放口所在水深的关系,并建立了污染物浓度与图像灰度关系的方程。利用该方程对射流在横流中测量的图像进行了浓度场计算,得到的结果与实际情况吻合较好,因此,该方法能广泛应用于物质扩散机理的研究。