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.

Initial Dilution of A Vertical Round Non-Buoyant Jet in Wavy Cross-Flow Environment

The phenomenon of wastewater discharged into coastal waters can be simplified as a turbulent jet under the effect of waves and currents. Previous studies have been carried out to investigate the jet behaviors under the current only or the wave only environment. To obtain better understanding of the jet behaviors in a realistic situation, a series of physical experiments on the initial dilution of a vertical round jet in the wavy cross-flow environment are conducted. The diluted processes of the jet are recorded by a high-resolution camcorder and the concentration fields of the jet are measured with a peristaltic suction pumping system. When the jet is discharged into the wavy cross-flow environment, a distinctive phenomenon, namely ＂effluent clouds＂, is observed. According to the quantitative measurements, the jet width in the wavy cross-flow environment increases more significantly than that does in the cross-flow only environment, indicating that the waves impose a positive effect on the enhancement of jet initial dilution. In order to generalize the experimental findings, a comprehensive velocity scale ua and a characteristic length scale l are introduced. Through dimensional analysis, it is found that the dimensionless centerline concentration trajectories cy/l is in proportion to 1/3 power of the dimensionless downstream distance x/l, and the dimensionless centerline dilution 2c aS Q/（u l） is proportional to the square of the dimensionless centerline trajectory cy/l. Several empirical equations are then derived by using the Froude number of cross-flow Frc as a reference coefficient. This paper provides a better understanding and new estimations of the jet initial dilution under the combined effect of waves and cross-flow current.

Experimental and numerical investigations on micromixing performance of multi-orifice cross-flow jet mixers

Multi-orifice cross-flow jet mixers(MOCJMs)are used in various industrial applications due to their excellent mixing efficiency,but few studies have focused on the micromixing performance of MOCJMs.Herein,the flow characteristics and micromixing performance inside the MOCJM were investigated using experiments and computational fluid dynamics(CFD)simulations based on the Villermaux/Dushman system and the finite-rate/modified eddy-dissipation model.The optimal A value was correlated with the characteristic parameters of MOCJMs to develop a CFD calculation method applicable to the study of the micromixing performance of the MOCJMs.Then the micromixing efficiency was evaluated using the segregation index XS,and the effects of operational and geometric parameters such as mixing flow Reynolds number(ReM),flow ratio(RF),total jet area(ST),the number of jet orifices(n),and outlet configuration on the micromixing efficiency were investigated.It was found that the intensive turbulent region generated by interactions between jets,as well as between jets and crossflows,facilitated rapid reactions.XS decreased with increasing ReM and decreasing RF.Furthermore,MOCJMs with lower ST,four jet orifices,and the narrower outlet configuration demonstrated a better micromixing efficiency.This study contributes to a deeper understanding of the micromixing performance of MOCJMs and provides valuable guidance for their design,optimization,and industrial application.

Finite Element Analysis for Magneto-Convection Heat Transfer Performance in Vertical Wavy Surface Enclosure:Fin Size Impact

The goal of this paper is to represent a numerical study of magnetohydrodynamic mixed convection heat transfer in a lid-driven vertical wavy enclosure with a fin attached to the bottomwall.We use a finite elementmethod based on Galerkin weighted residual(GWR)techniques to set up the appropriate governing equations for the present flow model.We have conducted a parametric investigation to examine the impact of Hartmann and Richardson numbers on the flow pattern and heat transmission features inside a wavy cavity.We graphically represent the numerical results,such as isotherms,streamlines,velocity profiles,local and mean Nusselt numbers,and average surface temperature.Comparisons between the results of this work and previously published work in a literature review have been produced to examine the reliability and consistency of the data.The different sizes of the fin surface significantly impact flow creation and temperature fields.Additionally,the long fin size is necessary to enhance the heat transfer rate on the right surface at large Richardson numbers and low Hartmann numbers.Fin surfaces can significantly increase the mixing of fluid inside the enclosure,which can mean reductions in reaction times and operating costs,along with increases in heat transfer and efficiency.

Research on the Influence of Raceway Waviness on the Vibration Characteristics of Deep Groove Ball Bearings

The dynamics model of a 2-degree-of-freedom deep groove ball bearing is established by incorporating the raceway surface waviness model comprising multiple sinusoidal functions superposition.The model is solved using the fourth-order Runge-Kutta method to obtain the vibration characteristics including displacement,velocity,acceleration,and frequency of the bearing.Validation of the model is accomplished through comparison with theoretical vibration frequencies.The influence of the amplitude of waviness of the inner and outer ring raceway surfaces of deep groove ball bearings on the vibration displacement,peak-to-peak vibration displacement and root-mean-square vibration acceleration is analyzed,and the results show that as the amplitude of the inner and outer ring raceway surfaces waviness increases,all the vibration characteristic indexes increase,indicating that the vibration amplitude of the bearings as well as the energy of the waviness-induced shock waveforms increase with the increase of the amplitude of the waviness.

Modeling of Mixed Convection in a Lid Driven Wavy Enclosure with Two Square Blocks Placed at Different Positions

The purpose of this paper is to investigate the simulation of mixed convection in a lid-driven wavy enclosure with blocks positioned at various positions. This study also examined the impact of the longitudinal position of the heated block on heat transfer enhancement. The Galerkin weighted residual finite element method is employed to computationally solve the governing equations of Navier-Stokes, thermal energy, and mass conservation. The enclosure consists of two square heated blocks strategically placed at different heights—firstly, one set is closer to the bottom surface;secondly, one set is nearer to the middle area and finally, one set is closer to the upper undulating surface of the enclosure. The wavy top wall’s thermal insulation, along with active heating of the bottom wall and blocks, generates a dynamic convective atmosphere. In addition, the left wall ascends as the right wall falls, causing the flow formed by the lid. The study investigates the impact of the Richardson number on many factors, such as streamlines, isotherms, dimensionless temperature, velocity profiles, and average Nusselt numbers. These impacts are depicted through graphical illustrations. In all instances, two counter-rotating eddies were generated within the cage. Higher rotating speed consistently leads to improved performance, irrespective of other characteristics. Furthermore, an ideal amalgamation of the regulating factors would lead to increased heat transmission.

Fluid Flow and Mixed Heat Transfer in a Horizontal Channel with an Open Cavity and Wavy Wall

Heat exchangers are utilized extensively in different industries and technologies.Consequently,optimizing heat exchangers has been a major concern among researchers.Although various studies have been conducted to improve the heat transfer rate,the use of a wavy wall in the presence of different types of heat transfer mechanisms has not been investigated.This study thus investigates the mixed heat transmission behavior of fluid in a horizontal channel with a cavity and a hot,wavy wall.The fluid flow in the channel is considered laminar,and the governing equations including continuity,momentum,and energy are all solved numerically.The numerical solution is stabilized by using a first-order multi-dimensional characteristic-based scheme in combination with a fifth-order Runge-Kutta method.The flow and heat transfer effects of varying Richardson numbers,Reynolds numbers,wave amplitude,wavelength,channel height,and cavity width are examined.The results indicate that the mean Nusselt number increases with an increase in Reynolds number,wave amplitude,and cavity width,while it decreases with an increase in Richardson number,wavelength,and channel height.The minimum Nusselt number is calculated to be 0.7,whereas the maximum Nusselt number is 27.09.The Nusselt number has only increased by 40%in the higher depths of the cavity,despite the Richardson number being 10,000 times larger.But this figure increases to 130%at lower depths.The mean Nusselt number is thus significantly influenced by channel height and cavity width.The influence of wave amplitude on the mean Nusselt number is twice that of wavelength.

Simulation of Natural Convection Flow with Magneto-Hydrodynamics in a Wavy Top Enclosure with a Semi-Circular Heater

Natural convection flow in enclosure has different applications such as room ventilation, heat exchangers, the cooling system of a building etc. The Finite-Element method based on the Galerkin weighted residual approach is used to solve two-dimensional governing mass, momentum and energy-equations for natural convection flow in the presence of a magnetic field on a roof top with semi-circular heater. In the enclosure the horizontal lower wall was heated, the vertical two walls were adiabatic, inside the semi-circular heater, the wavy top wall cooled. The parameters Rayleigh number, Hartmann number and Prandtl number are considered. The effects of the Hartmann number and Rayleigh number on the streamlines, isotherms, velocity profiles and average Nusselt number are examined graphically. The local Nusselt number and the average Nusselt number of the heated portion of the enclosure with the semi-circular heater are presented in this paper. Finally, for the validation of the existing work, the current results are compared with published results and the auspicious agreement is achieved.

黄土堆填场地转化为泥石流物质过程--以兰州市碱水沟为例

黄土地区人工堆填场地是近几年兰州市拓展城市用地空间的一个新举措,在场地边缘形成较多堆填边坡,成为参与泥石流的潜在物质。以兰州市碱水沟“4•19”泥石流灾害为例,结合粒径分析试验、扫描电镜图像及野外入渗试验,探讨其特征及运行模式,并提出相应的治理建议。结果表明:1)黄土地区人工堆填体颗粒粒径<1.000 mm的物质约占11.4%~55.2%,有利于泥石流启动;2)以2个相距170 m的泥位调查断面做比较,下游断面流量增加2.5倍,说明入渗引起的黄土湿陷能促进泥石流物质的转化率;3)入渗试验表明:黄土堆填场地渗透性强,低水头条件下8 min左右达到稳定入渗状态,高水头条件下12 min左右达到稳定入渗状态,能在较短的时间内使土壤软化,影响人工堆填场边坡稳定,提高泥石流物质转化速度;4)黄土地区人工堆积体场地诱发的泥石流流动模式复杂、多变,兼具波状流和间歇流的特点。在此基础上,笔者提出过程管理和重点防护相结合的防治模式。

爆炸焊接铜/钢复合管界面组织表征与性能研究

为了研究应用于压力容器的管道或承压部件的铜/钢双金属复合管材料中晶粒存在形式和力学性能之间的关系,通过爆炸焊技术获得了T2铜/316L不锈钢复合管,并对其界面形貌与微观组织进行分析。结果表明,T2铜/316L不锈钢复合管结合界面处呈现平直界面和周期性波状界面,波形结合区域的平均波长203μm、波高58μm。复合管结合界面两侧的元素发生互扩散,扩散层厚度为1μm。界面处Fe侧晶粒尺寸较小,随着结合界面距离的增加晶粒尺寸逐渐变大。通过纳米压痕试验发现,波峰处界面的纳米压痕结果达到了3.16 GPa,波谷处的纳米压痕结果达到了2.44 GPa,同时波峰处界面附近区域的纳米压痕结果均高于波谷处,Fe侧纳米压痕结果均高于Cu侧。纳米压痕试验获得的力学性能分布规律和微观组织的分布规律相一致。

定常吸吹气作用下波浪圆柱主动减阻机制

针对圆柱绕流减阻抑振问题,对波浪圆柱采用定常吸吹气主动控制手段,在雷诺数Re=3000情况下,利用大涡模拟数值方法,研究吸吹气方式、方位角(吹吸气装置与来流反方向夹角)、动量系数对波浪圆柱的升阻力特性、时均压力、速度分布、近尾迹流动结构发展及其减阻抑振的影响规律。结果表明:定常吸气控制比吹气控制对波浪圆柱减阻抑振效果更好;定常吸气方位角位于迎风面时波浪圆柱的升阻力系数随动量系数的增大而减小,位于背风面时则呈先减小后增大再减小趋势,这主要归因于定常吸气通过吸收低速度流体延缓流动分离,削弱了尾流的顺流向雷诺应力和横流向雷诺应力,降低了柱体前后表面的压差,波浪圆柱的近尾迹宽度在横向上显著变窄;在适当的吸气动量系数及方位角工况下,Saddle截面近尾迹回流区基本被消除,下游出现“带状涡”,升阻力波动得到了显著控制,平均阻力系数较未受控制波浪圆柱减少83.84%。

三角形排列波浪锥柱绕流流动特性数值分析

采用大涡模拟方法,分析了亚临界雷诺数为3 900时三角形排列波浪锥柱的横流向间距比和顺流向间距比对其升阻力特性、尾流干涉效应及三维流动结构等的影响.结果表明,上游2个波浪锥柱的升阻力特性受下游波浪锥柱影响较小,下游波浪锥柱处于上游双波浪锥柱尾流中,其升阻力特性受横流向间距比和顺流向间距比影响更为显著.3个波浪锥柱间的流动状态可分为邻近干扰、漩涡撞击和涡相互作用状态.在漩涡撞击状态下,上游波浪锥柱尾涡得以发展充分,周期性撞击在下游波浪锥柱表面,从而产生较大的脉动升力.横流向间距比、顺流向间距比分别为3和6时,下游波浪锥柱脉动升力系数较单直圆柱提升了20.93倍.

聚丙烯纤维混凝土力学性能试验

为了探究不同类型、不同掺量的聚丙烯纤维对混凝土力学性能的作用效果,在混凝土材料中加入3种不同类型的聚丙烯纤维(波浪型聚丙烯纤维、压花型聚丙烯纤维、单丝型聚丙烯纤维),并分别使用不同掺量(0、0.08%、0.11%、0.14%、0.17%、0.20%)作为水平变量,对聚丙烯纤维试块进行抗压强度试验、劈裂抗拉强度试验、轴心抗压强度试验.研究发现:波浪型聚丙烯纤维掺量为0.17%时,混凝土抗压强度最佳;单丝型聚丙烯纤维掺量为0.20%时,混凝土的劈裂抗拉强度最佳;单丝型聚丙烯纤维掺量为0.17%时,对于混凝土的抗折强度有较好作用效果.

亚临界雷诺数下串列双波浪锥柱绕流数值模拟

针对风力俘能结构布局问题,基于大涡模拟(LES)方法,在亚临界雷诺数下(Re=3900)研究有限长串列双波浪锥柱的升阻力特性及其流动结构随间距比的变化规律。结果表明:由于上游波浪锥柱的影响,下游波浪锥柱的脉动升力系数大幅增大,当间距比为3时,表面时均压力系数分布形式呈反向分布;随间距比增加,上游波浪锥柱尾流充分发展,并产生大量肋状涡撞击在下游波浪锥柱表面,下游波浪锥柱产生大的脉动升力,相较于单直圆柱提升约15.3倍,阻力系数降低约0.172。所得结果可为风力俘能结构布局提供有益参考。

含沙条件下泵站进水池控涡技术研究

含沙水流会对沿黄泵站造成严重的磨损破坏。泵站进水池漩涡的存在将会加重水泵磨损,严重影响水泵的运行寿命。为探究含沙条件下泵站进水池控涡技术,基于仿生学原理研发了一种带波状前缘翼型喇叭口的消涡装置,并通过模型试验,在清水和含沙水两种环境下,研究波状前缘翼型喇叭口对进水池内漩涡的影响特性。结果表明:无论在清水还是含沙水条件下,波状前缘翼型喇叭口均能有效抑制附底涡的产生、降低附底涡的出现频率、减小进水管内水流的预旋强度,有利于改善水泵的进水流态,防止泥沙磨损的进一步加剧。

基于圆台波浪形换热管的潜热储热单元性能分析

为提高潜热储热单元(latent heat storage unit,LHSU)的储热性能,提出了三种优化换热管结构的新型LHSU,分别为圆台形换热管潜热储热单元、波浪形换热管潜热储热单元和圆台波浪形换热管潜热储热单元(frustum wavy heat transfer tube latent heat storage unit,FW-LHSU)。基于数值模拟方法,比较了传统圆柱形换热管潜热储热单元(cylindrical heat transfer tube latent heat storage unit,C-LHSU)和三种新型LHSU的储热性能。此外,针对FW-LHSU研究了换热管壁面倾斜角度对储热性能的影响。结果发现,所提出的三种新型换热管结构均能增强储热性能,其中FW-LHSU储热效果最好,与C-LHSU相比,FW-LHSU的熔化时间缩短了32.64%,储热速率密度提高了48.1%。当增加FW-LHSU的换热管壁面倾斜角度时,其储热性能可进一步提高。当换热管倾斜角度从2°增加到8°时,FW-LHSU的储热时间可缩短37.00%、储热速率密度可提高48.44%。

考虑波纹度激励的齿轮系统动态特性研究

波纹度是一种偏向于微观的位移缺陷,对系统动力学响应具有一定影响。该文考虑波纹度激励对齿轮系统产生的影响,采用集中参数法建立了多自由度斜齿轮-轴承平移扭转耦合动力学模型,应用Runge-kutta算法对系统微分方程进行求解处理,通过分析对比该文提出的模型响应与忽略波纹度的斜齿轮-轴承模型响应的幅频响应、瀑布图、时域图以及频谱,揭示了波纹度对系统动态特性的影响规律。仿真结果表明:低转速时,波纹度对系统响应的影响不明显,两种模型均出现明显的周期性和幅值调制现象,滚动体通过频率和齿轮啮合频率为系统的主要特征频率;随着转速增大,1/2啮合频率成分为两种模型响应的主要频率成分,两种模型均出现分频共振现象;随着转速进一步增大,忽略波纹度模型响应的主要频率依旧为啮合频率和轴承滚动体通过频率,该文所提出模型的响应中出现明显的从动齿轮波纹度激励频率成分,波纹度对系统高转速下的动力学响应有明显的影响。

滚动轴承波纹度对齿轮动态传递误差的影响

为了研究轴承波纹度制造误差对轴承-齿轮传动系统中齿轮动态传递误差的影响,构建了轴承滚道表面时变波纹度误差表征模型,建立了考虑轴承内外圈滚道表面波纹度幅值、波数以及时变齿轮啮合刚度的轴承-轴-齿轮系统耦合动力学模型,研究了齿轮传动系统支撑轴承内外圈滚道表面波纹度幅值和波数对齿轮动态传递误差的影响规律。仿真结果表明:输入轴支撑轴承存在波纹度误差时,其外圈滚道波纹度对齿轮动态传递误差的影响大于内圈滚道;输出轴非负载端支撑轴承存在波纹度误差时,其内外圈滚道波纹度对齿轮动态传递误差的影响相似;输出轴负载端支撑轴承存在波纹度误差时,其外圈滚道波纹度对齿轮动态传递误差的影响大于内圈滚道。

零质量射流下波浪前缘叶片气动性能数值研究

针对垂直轴风机叶片大攻角工况下因流动分离导致的失速及颤振抖振问题,引入零质量射流激励对波浪型前缘叶片进行流动分离控制.采用大涡模拟方法建立了波浪前缘叶片绕流数值模型,探究了主/被动耦合控制下叶片升阻力特性及其流动分离机理,分析了射流参数(射流位置、动量系数)对波浪前缘叶片气动性能及失速特性的影响机制,研究发现:受控前后大攻角下波浪型前缘能诱导产生较小尺度流向涡,降低后方大分离涡尺度,波浪前缘与零质量射流耦合控制对于大攻角下流动分离抑制较单一控制更优;零质量射流吹气时使前缘流向涡有更高的动能抵抗逆压梯度从而延迟流动分离,吸气时会吸走流向涡的低动量流体,抑制流向涡发展成大分离涡;射流布置在距基准前缘0.033c处,即位于前缘流向涡最前端,能最大程度地参与前缘流向涡的生成,升阻比的提升效果最好;且升阻比提升量随着动量系数增大而增大,但控制经济性在动量系数0.018时最优,研究结果为垂直轴风力机失速控制提供了有益参考.

表面波度对液体椭圆孔端面密封上游泵送特性的影响

表面波度与端面几何型槽的耦合影响使得密封性能的变化规律更为复杂。基于粗糙和波度表面假设,建立空化效应下端面椭圆孔液体上游泵送密封的理论分析模型,对上游泵送端面密封的压力分布和泄漏率进行数值求解计算,分析周向表面波度幅值、数量等几何参数和转速、密封压力等操作参数对开启力和泄漏率的影响规律。结果显示:表面波度使得密封端面产生更高的流体动压效果,并减弱上游泵送效果,容易导致密封介质的泄漏;随着波高和周向波数的增加,开启力略有增加;泄漏率随着波高的增加呈现正向增强趋势,但波数对泄漏率没有明显影响;在空化效应和表面波度的影响下,速度剪切产生的密封端面开启力可增加50%以上,并形成流体的完全上游泵送;密封压力和膜厚的增加,使得流体的上游泵送性能和密封性下降。