双柱双锥形液—流旋流分离管内流场的LDV诊断

本文采用ＴＳＩ二维ＬＤＶ系统,对一种双锥双柱形液－液旋流分离管内流场进行了全场范围的精细ＬＤＶ诊断,先后考试了处理量、压差比、溢流比和气芯等因素对旋流分离管内流场的影响,结果表明：该旋流分离管中下游区的切向速度呈较为明显的Ｒａｎｋｉｎｅ双涡结构,在上游位涡区中发现有未曾报道过的双峰分布现象;轴向速度由近轴处的上行流、近壁处的下行流以及介于两者之间的零速区组成,其中该零速区随旋流分离管截面的收缩而减     

双柱单锥型液-液旋流管内流场的激光诊断

应用激光测速仪，对一种双柱单锥型液 液旋流管内的流动结构，进行了全场范围内的多工况流动诊断研究．揭示出其切向速度由内旋流区和外旋流区构成，其中内旋流区中的速度分布符合准强制涡关系，外旋流区中的速度分布符合准自由涡关系；轴向速度由上行流动区和下行流动区构成，两者之间在直管段以零速点作分界，在锥体段则以零速区作过渡并伴随有一定的回流出现，且该过渡区或回流区的大小随锥体截面的收缩而减小，直到进入直管段后消失；各湍流量的分布以管芯处最大向外逐渐减小，沿轴向是直管段中的湍流度大于锥体段中的湍流度，而且湍流度在旋流管内具有各向异性的特性．     

液—液旋流分离管中强旋湍流的K—ε …

采用标准ｋ－ε湍流模型,对一种典型液－液旋流分离管中的强旋湍流进行了数值模拟研究。结果表明：该模型对切向速度的数值预报夸大了Ｒａｎｋｉｎｅ涡中的似固核范围。抹煞了似固核外的位涡区;对轴向速度的数值预报未给出心回流区;对其它流场参数的预报结果也都存在有明显的不合理之处。由此证明这种基于Ｂｏｕｓｓｉｎｅｓｑ假设的各向同性湍流模型,虽然在管道流、平面射流和无旋流等简单流动问题中经受住了大量计算实践的检验     

用LDV系统测量转盘萃取塔内流场

本文应用激光多普勒测速仪对二种转盘萃取塔模型进行切向速度、轴向速度和湍流度测量。实验结果表明，在ＲＤＣ是切向速度比较大，因而有较大的搅拌效果，它的内部流场比较均匀稳定，有利于传质，所以ＲＤＣ是广泛应用于化学工业中的一种液－液萃取设备。     

液-液旋流分离管中强旋湍流的k-ε数值模拟

采用标准k-ε湍流模型,对一种典型液-液旋流分离管中的强旋湍流进行了数值模拟研究.结果表明:该模型对切向速度的数值预报夸大了Rankine涡中的似固核范围,抹煞了似固核外的位涡区;对轴向速度的数值预报未给出中心回流区;对其它流场参数的预报结果也都存在有明显的不合理之处.由此证明这种基于Boussinesq假设的各向同性湍流模型,虽然在管道流、平面射流和无旋流等简单流动问题中经受住了大量计算实践的检验,但在强旋湍流的数值预报方面的确存在有较大缺陷.此问题的解决有赖于对该模型进行必要的修正或转而采用更加高级的各向异性模型.     

疏液壁面上亲液杂质对滑移特性的影响

纳米流动系统具有高效、经济等优势,在众多领域具有广泛的应用前景.因该类系统具有极高的表面积体积比,致使界面滑移效应对流动具有显著影响.论文采用非平衡分子动力学模拟方法,研究了疏液壁面表层混入少量亲液原子时纳米通道内液体的滑移特性,并基于分子动理论解释了其影响机制.研究发现,亲液杂质(均布或集中)对液体法向密度振荡程度影响较弱,但会显著改变壁面附近类固体层的分布和液体滑移规律;随亲液杂质占比增加,液体类固体现象更趋明显,壁面处液体接触密度也线性增大,但通道内液体平均速度逐渐降低,滑移长度也迅速减小;相比于集中的亲液杂质,均匀分布亲液杂质对滑移的弱化效应更强.如当亲液杂质占比为28%时,其滑移长度比单纯疏液表面的降低率从50%扩大至56%.基于分子动理论的分析发现,亲液杂质会导致杂质原子附近第一液体层内的原子发生跃迁的能垒加大,即弱化了液体原子的流向跃迁行为,从而降低了滑移量;相比于集中杂质,均匀分布的杂质还会降低固液间的非公度性,致使滑移特性破坏更严重.     

充液管道系统的模态分析

考虑管道与液体之间的泊松耦合与连接耦合,推导了低频情况下的充液直管轴向、横向振动传递矩阵与弯管单元的传递矩阵,引入了弯管弯曲因子,对－“L”形充液管系进行了研究,使用ANSYS有限元分析软件与传递矩阵法计算了两种边界条件下充液、充所管系的模态频率与模态振型,结果表明,气体与管道之间的耦合作用对管系模态的影响可忽略;而对充液管系而言,因液耦合作用不能忽略。     

不等径颗粒间液桥力学参数及形态的试验研究

作为一种自然界中广泛存在的力, 液桥力的研究对制药、重金属回收、颗粒分离等领域具有十分重要的意义. 利用纳米多功能拉伸试验机测量不等径颗粒间液桥拉伸过程中的液桥力?位移曲线, 同时配合CCD工业相机记录拉伸全过程液桥形态的变化. 首先分析了液桥力?位移曲线形态、最大液桥力、断裂距离随粒径比及液桥体积的变化规律, 其次基于圆环假设及Y-L方程对本文试验结果的合理性进行验算, 最后针对圆环假设在液桥力计算中存在的不足分析了其原因, 并结合重力对液桥形态的影响对液桥拉伸全过程的形态变化进行了具体分析. 结果表明: 最大液桥力受粒径比的影响较大而受液桥体积的影响较小, 与最大液桥力相反, 断裂距离受液桥体积的影响较大而受粒径比的影响较小; 圆环假设可以较好地预测最大液桥力大小但对拉伸过程中的液桥力预测不准, 这是由于当液桥力达到最大值后液桥的外轮廓已不能用圆环表示; 根据重力对液桥形态的影响, 将拉伸过程液桥外轮廓的变化简化为重力影响可以忽略时的圆环形?抛物线形, 重力影响处于过渡阶段或影响较小时的长轴与短轴之比不断增大的椭圆形, 以及重力影响不可忽略时的“冷却塔形”?双曲线形.      

二维激光多普勒测速仪用于测量旋转机械的内部流动

本文介绍了用二维激光多普勒测速仪测量离心式风机的叶轮和蜗壳的旋转流场的原理和实际过程,得到了径向速度、切向速度和湍流度等流体力学参数沿径向和轴向的分布曲线并对实验方法和实验结果进行了讨论。     

液粘离合器摩擦特性及热负荷特性研究

本文针对新型液粘离合器的摩擦系数和热负荷进行试验研究,其中摩擦系数是液粘离合器特性的核心衡量指标,通过摩擦学理论研究,确定液粘离合器的摩擦状态,找到适用的试验方法对其进行了测试计算,根据结果进行分析,得出液粘离合器在不同转速差、不同入口油温以及不同正压力的摩滑状态时摩擦系数的变化趋势,并得到不同转速差对摩擦系数的影响公式;应用润滑油流量和摩擦功率损失计算液粘离合器的热平衡温度,并通过试验对摩擦片的热负荷进行了研究,对比分析液粘离合器热量散失的方式,发现液粘离合器摩擦片摩滑状态的热负荷计算公式有待改进;针对摩擦片轴向温度分布不平衡,制定了润滑流量的匹配结构优化方案.     

Velocity distributions in a hydrocyclone separator

 The internal three-dimensional flow field in a hydrocyclone was studied using laser velocimetry. Seven axial planes were investigated for three different inlet flow rates and three independent and different rejects rates. Results at each measurement plane showed that the measured tangential velocity profile behaves like a forced vortex at the region near the air core, and like a free vortex in the outer portion of the flow. The peak nondimensional tangential velocity decreases as the distance from the inlet region increases, however, the peak dimensional tangential velocity increases as the distance from the inlet region increases. The nondimensional peak tangential velocities are approximately equal for all of the flow rates. The magnitude of the tangential velocity increased in the inner forced vortex region as the rejects rate was increased. Backflows exist in the axial velocity profile near the inlet region, but these reversed flows disappear in the exit region. The dimensional vorticity is proportional to inlet flow rate and decreases with increasing rejects flow rates. Received: 27 February 2001/Accepted: 19 June 2001     

Theoretical study of the flow field inside a hydrocyclone with vortex finder diameter greater than that of apex opening—I. Laminar case

The axi-symmetric laminar boundary layers, formed on the conical surface and under the cyclone roof, have been calculated by Pohlhausen's method assuming that the tangential velocity outside boundary layers varies as r ^?n up to the point where boundary layers meet solid body rotating liquid column and thereafter as r—as found in experiments—where r is the distance from the axis of the cone and n is flow pattern constant. Point of interaction of the boundary layers with solid body rotating liquid column has been taken from experimental results obtained with a hydrocyclone having vortex finder diameter greater than that of apex opening. Results show that there is no possibility of separation of boundary layers from cyclone wall.     

Influence of mass-flow ratio of inner to outer secondary air on gas–particle flow near a swirl burner

The influence of mass-flow-rate ratio of inner to outer secondary air on gas–particle flow characteristics was determined in the near-burner region of a centrally fuel-rich swirl coal combustion burner. Velocity and particle volume flux profiles and normalized particle number concentrations were obtained. Peaks in tangential mean velocity and three-dimensional root-mean-square fluctuation velocities were found to decrease as the mass-flow-rate ratio increased. Moreover, the peaks in the mean axial velocities and particle volume flux near the wall increased, whereas those near the chamber axis decreased. Simultaneously, both recirculation zone and swirl number decreased as the mass-flow-rate ratio increased.     

Dynamics of heavy particles in two swirling jets

We report flow visualisations and laser Doppler anemometry (LDA) velocity measurements in the near field of two swirling jets. The Reynolds number based on jet diameter and bulk velocity at the nozzle exit is 1.4 × 10⁵. In the first jet, a small recirculation region is formed around the jet axis, while, in the second, the streamwise velocity remains positive and overshoots near the jet centre. In both cases, flow visualisations show that the vortex core of the jets is depleted of seeding particles. By using time-averaged distributions of the streamwise and tangential velocities measured at the nozzle outlet, the dynamics of the particles is simulated, by integrating their simplified equations of motion. The particles trajectory thus computed agrees well with that observed in the flow visualisations. Although the turbulence intensity is substantially different in the core of the two jets, its effect on the seeding concentration is localised near the edge of the core.     

An experimental investigation of pneumatic swirl flow induced by a three lobed helical pipe

This paper presents a discussion of the results and conclusions drawn from a series of experiments conducted to investigate the swirl flow that are generated by a three lobed helical pipe mounted within a laboratory scale pneumatic conveying rig. The experiments employed Laser Doppler Anemometry (LDA) to quantify the strength of the induced vortex formations and the decay rates of the observed downstream swirl flows over a range of Reynolds number in the turbulent regime. Instantaneous point velocity measurements were resolved in three directions across regular measurement grids transcribed across parallel planes located at four distances downstream of the swirl inducing pipe section. The equivalent axial, radial and tangential velocities were subsequently computed at these grids points. The degree of swirl measured across each measurement plane was expressed in terms of a defined swirl number.It was concluded that the three lobed helical pipe gave rise to a wall jet type of swirl whose rate of observed downstream decay is related to the Reynolds number of the upstream flow and the distance downstream of the swirl pipe. The decay rates for the swirl flows were found to be inversely proportional to the Reynolds number of the upstream flow. The swirl pipe was observed to create a redistribution of the downstream velocity field from axial to tangential, accompanied by a transfer of axial to angular momentum. The findings of this paper are believed to improve understanding to assist the selective use of swirl flow within lean phase particles pneumatic transport systems.     

Stereo particle image velocimetry applied to a vortex pipe flow

Stereo particle image velocimetry (PIV) has been employed to study a vortex generated via tangential injection of water in a 2.25 inch (57 mm) diameter pipe for Reynolds numbers ranging from 1,118 to 63,367. Methods of decreasing pipe-induced optical distortion and the PIV calibration technique are addressed. The mean velocity field analyses have shown spatial similarity and revealed four distinct flow regions starting from the central axis of rotation to the pipe wall in the vortex flows. Turbulence statistical data and vortex core location data suggest that velocity fluctuations are due to the axis of the in-line vortex distorting in the shape of a spiral.     

Effect of bubbles on the turbulence near the exit of a liquid jet

The objective of this paper is to examine the effect of bubbles on the turbulence levels of a water jet. Simultaneous measurements of the axial and radial velocity components were taken in a bubbly jet with a Laser Doppler Velocimeter (LDV) and then compared to the velocities of a single phase jet at the same liquid flow rate. Mean bubble diameters ranged from 0.6 to 2 mm and the void fractions were up to about 20%. The liquid Reynolds numbers were from 5,000 to 10,000 approximately. The measurements extended to from an axial distance of 4–12 cm. It was observed that bubbles did not affect significantly the average velocity profiles in the jet. However bubbles increased the turbulence intensities in the core of the jet near the jet exit. The increase in turbulence intensities was more pronounced at lower Reynolds numbers and at higher void fractions.     

不同参数下环形通道内湍流旋流流动的模拟

应用一种合理考虑湍流一旋流相互作用及湍流脉动各向异性的新的代数ＲｅｙｎｏｌｄＳ应力模型,对环形通道内的湍流旋流流动进行了数值模拟．研究了旋流数、进口轴向速度和内外半径比等参数对环形通道内湍流旋流流动的影响,以及由此产生的流场变化对强化环形通道内传热的作用．