煤液化调节阀流场演变特性的测试与分析

利用粒子图像测速技术（particle image velocimetry,简称PIV）和涡量分析原理对调节阀不同工况下的流场信息进行测量,研究了进口压力对液压调节阀速度场、涡量场及湍动能的影响。结果表明：调节阀节流口处有对冲射流,其在阀芯头部下游汇合后形成向下游的整体喷射;节流口下游的油液轴向速度先减小后增大,在喉部末尾处附近趋于稳定;在靠近壁面区域油液径向流动速度都较低,在流道中心区域流动速度较高;阀芯头部和下游流道存在由速度梯度引起的介质回流旋涡,高涡量区域主要分布在阀芯头部和壁面处,强的正涡与负涡呈2条斜形宽带分布;阀芯头部为高涡量区且具有贴壁特征,壁面附近高涡量区向下游延展;随着调节阀进口压力的增大,阀口流量、流场高速分布区域、旋涡的强度和尺度以及湍动能均随之增大。     

车载高压气动减压阀压力场与速度场研究

分析了氢能源汽车输氢系统的70 MPa两级气动减压过程,取得了两级减压阀各阀腔内部的压力场和速度场分布规律.研究结果表明:两级气动减压阀组的阀腔压力分布可分为上游压力区、中间压力区和下游压力区;第一级减压阀和第二级减压阀的阀口处气体均为超音速流动状态,2个减压阀出口的封闭直角区域均存在低速涡流现象.可以通过计算流体动力学(CFD)方法得到流场分布的数据,为车载减压阀组和锥形阀芯的形状与结构设计提供理论依据.     

煤液化热高分液控阀空蚀磨损耦合研究

采用煤液化热高分液控阀的实际操作条件、工艺介质和结构特性,基于两相空化流动方程、Lagrangian固体颗粒控制方程和RNG k-ε湍流模型,开展空蚀和磨损的耦合计算。计算结果表明:在阀芯的出口处,由于流速降低导致的分离现象,会出现回流区和空化带;在阀芯和阀座的间隙处,由于局部压力降低至液相的饱和蒸汽压以下,阀芯壁面存在明显的空化区域,易发生空蚀;阀座的近壁面存在高速固体颗粒的团聚现象,易发生磨损。实际失效案例与数值计算的结果基本一致,验证了数值计算的可靠性。     

锥形节流阀中背压对空化流场的影响

对锥形节流阀进行了流场模拟及其特性研究,分析了流道背压对锥形节流阀流道内压力、速度和空化区域分布的影响。研究结果表明:锥形节流阀阀腔内节流口后部区域,流体流速增高、压力降低,是空化发生的主要区域。随着背压的减小,空化区域不断增大,空化强度增强。背压越小,空化区域越靠近阀座壁面,空化强度越大。研究结论可为工程人员设计高性能液压阀提供了理论依据。     

倒角阀座式水压锥阀空化射流动态行为数值模拟

使用可压缩的VOF空化两相流算法对倒角型阀座水压锥阀的空化射流进行了三维瞬态流场仿真。模拟结果揭示,空化结构首先在狭窄的倒角阀座流道内以附着空化的形式出现;在压差为4.4 MPa的工况条件下,空化分布集中在3个区域,阀座流道内及阀芯后沿的附着型空化,阀座流道至阀芯后沿的漩涡空化。射流势核在阀座流道入口及阀芯后沿均有分离流现象,从而诱发附着型空化;而大尺寸漩涡结构主要分布于射流势核的自由剪切层侧,漩涡空化亦相应地集中在自由剪切层侧,壁面侧偶发性形成薄层型漩涡空化。由于整体的空化行为涉及多个不同类型空化的耦合,其动态演变的周期特性受到干扰。阀座流道后部的脱落空化伴有明显的三维漩涡结构,阀芯后沿的漩涡空化与附着空化通过耦合作用形成大尺寸汽泡结构,揭示了后沿下游稀疏分布的大尺寸空化结构的产生过程。通过开展三维瞬态模拟,结合流场结构探索了空化射流的动态特性,从流体力学的层面解释了实验观测到的空化形态及分布规律。     

煤液化调节阀湍流特性及稳定性研究

针对湍流流动对煤液化调节阀内部流场稳定性影响,基于粒子图像测速技术(Particle Image Velocimetry, PIV)和能量梯度理论对煤液化调节阀的脉动流场信息进行测量和表征。采用数值模拟和实验相结合的方法,探究了1.2,1.4,1.6,1.8 MPa 4种进口压力条件下(出口压力固定为1 MPa、开度固定为60%)脉动速度均方根、湍流动能等湍流特性参数的变化规律,并结合能量梯度理论对调节阀内流动稳定性展开分析。结果表明,脉动速度均方根的分布与湍流动能的分布具有相似性,高速主流区域位于阀芯头部低速流体的交界处,脉动速度均方根及湍动能值随流速增大而升高,并在轴向位置x为29.73 mm处达到峰值;高速主流与周围低速流体自身剪切产生的速度梯度是造成流场失稳的主要因素;整个流场最不稳定的位置分布在节流口下方阀芯和阀座壁面位置以及高速主流核心区外的剪切层内,进一步揭示了煤液化调节阀失稳机理。     

双阀座止动式旋塞阀设计及接触应力分析

针对目前常用的旋塞阀容易发生转动失效的问题设计了一种双阀座止动式旋塞阀。该旋塞阀在发生井喷关闭后,可有效减小旋塞阀球形阀芯和阀座之间的接触应力,减少球形阀芯的变形,从而使旋塞阀开启转动力矩变小,并能保证其密封的可靠性,有效解决了旋塞阀容易发生转动失效的问题;另外还通过建立球形阀芯和阀座接触的力学模型和ansys有限元分析软件分别对旋塞阀工作时球形阀芯和阀座的接触应力进行了理论计算和有限元分析。     

稳压器喷雾阀阀芯倒角尺寸对流动的影响

V型旋转式阀芯具有流阻小,切断性能好,调节精度较高的特点。为了减小阀芯旋转时流体在阀芯和阀座棱边上剪切力以及阀门形阻系数,通常在阀芯的棱边上加工倒角来达到此目的,研究稳压器喷雾阀V型阀芯棱边不同倒角尺寸时,阀内流体流动时在阀芯与阀座上的产生的剪切力大小,以及阀芯棱边取不同倒角尺寸时对流动的各参数的影响。采用CFD软件fluent,基于RANS方程,采用有限体积法进行空间离散,使用K-ε湍流模型和SIMPLE算法,针对阀芯不同的倒角尺寸,计算稳压器喷雾阀V型阀芯在关闭时阀门的体积流量,湍流参数,壁面剪切力,形阻系数等各种参数。得到阀芯倒角对流动参数的影响规律。     

非全周开口的液压滑阀内部流场的CFD解析

对非全周开口滑阀内部流道进行了三维建模,并用CFD软件fluent对模型进行计算分析。研究发现滑阀阀腔内的流场在节流口前后变化较大,在阀腔和阀座的拐角处存在涡流,而增大阀腔内的压力可以减小涡流的形成。阀芯受到的稳态液动力随着流量的增大而增大,随着阀口开度的增大而减小。滑阀进出口的压力损失主要是由于油液在节流口处的节流特性引起的,而阀腔内部的涡流和油液的黏性摩擦引起的压力损失只占很小一部分。     

进口小型电磁阀检测与维修一例

图1所示为一台国外引进气动设备上的一个小型电磁阀的结构原理图。这是一个先导式二位三通截止阀。主阀由阀体、阀座、阀芯(由阀芯杆、小密封垫、大密封垫组成)和端盖构成。旋出端盖,可将阀座连同阀芯一起从阀体中取出。阀的工作原理是:电磁先导阀的线圈断电时,在弹簧的作用下,动铁芯下部的胶垫堵住喷口a,切断气源通往主阀芯右端的气路,主阀阀芯右端腔室与先导阀排气口b相通,大密封垫8的右侧无气压作用,而主阀阀座内腔与气源P相通,压缩空气同时作用在大密封垫8的左侧与小密封垫4的右侧,但由于它们的受压面积不等,     

正反接方式下角座阀内介质的流动特性分析

针对不同连接方式下角座阀内介质的流动特性开展数值模拟和实验研究。采用RNG k-ε湍流模型, 结合标准壁面函数法, 计算阀内流场。通过流量系数的实验数据和计算结果对比, 验证了数学模型和计算方法的准确性。在此基础上, 对正接和反接方式下角座阀内的流动核心区域、速度场和压力场进行对比分析。结果表明:正接方式下, 角座阀具较高的流通能力, 阀芯附近流动核心区域的面积更大, 并且在阀门出口下侧存在较大的漩涡, 会导致流阻增加。两种连接方式下, 阀芯中央截面处均出现二次流, 其中正接方式具有更高的流动不稳定性。     

液压锥阀内部流场的可视化分析

利用Fluent计算流体软件对液压锥阀的内部流场进行分析,经对阀芯不同开口量的可视化分析,采用标;住紊流模型模拟了内部流体的流动状态及漩涡的产生区域,并对其稳态液动力进行了分析,可为阀的整体性能和结构优化提供参考依据：     

联体泵-马达壳体内流场功率损失特性

联体泵-马达工作过程中由于流场功率损失过大,造成摩擦副磨损、压力供给不足、旋转部件发热等问题,降低整机的可靠性和寿命。采用了Mixture多相流模型及自编程的网格变形运动控制程序,建立了联体泵-马达壳体内部流场功率损失特性数值仿真模型。通过分析连体泵-马达壳体内油-空气两相流场中涡结构和湍流参数,揭示了壳体内流场功率损失产生机理及分布特性,并研究了转速和泵斜盘倾角对功率损失的影响规律。结果表明:流场涡结构及湍动能较高区域均集中在柱塞及缸体转动区域,该区域的搅拌损失占比为98.91%,湍流耗散损失占比为60.66%,是壳体内流场功率损失主要来源区。转速的增加导致流场湍动能升高,流场总损失增加;转速从955 r/min增大至3000 r/min后,流场总损失增加了1441.36 W。泵斜盘倾角的变大,使马达侧转速增加,流场更紊乱,流场总损失增加;泵斜盘倾角从0°增大至17.5°,流场总损失增加了1077.04 W。     

Two-phase non-linear model for the flow through stenosed blood vessels

Pulsatile flow of a two-phase model for blood flow through arterial stenosis is analyzed through a mathematical analysis. The effects of pulsatility, stenosis, peripheral layer and non-Newtonian behavior of blood, assuming the blood in the core region as a Herschel-Bulkley fluid and the plasma in the peripheral layer as a Newtonian fluid, are discussed. A perturbation method is used to solve the resulting system of non-linear quasi-steady differential equations. The expressions for velocity, wall shear stress, plug core radius, flow rate and resistance to flow are obtained. It is noticed that the plug core radius and resistance to flow increase as the stenosis size increases while all other parameters held constant The wall shear stress increases with the increase of yield stress while keeping other parameters as invariables. It is observed that the velocity increases with the axial distance in the stenosed region of the tube upto the maximum projection of the stenosis. Currently on leave from Department of Mathematics, Crescent Engineering College Vandalur, Chennai-600 048, Tamil Nadu, India.     

Numerical simulation of cavitation surge and vortical flows in a diffuser with swirling flow

The strong swirling flow at the exit of the runner of a Francis turbine at part load causes flow instabilities and cavitation surges in the draft tube, deteriorating the performance of the hydraulic power system. The unsteady cavitating turbulent flow in the draft tube is simplified and modeled by a diffuser with swirling flow using the Scale-adaptive simulation method. Unsteady characteristics of the vortex rope structure and the underlying mechanisms for the interactions between the cavitation and the vortices are both revealed. The generation and evolution of the vortex rope structures are demonstrated with the help of the iso-surfaces of the vapor volume fraction and the Qcriterion. Analysis based on the vorticity transport equation suggests that the vortex dilatation term is much larger along the cavity interface in the diffuser inlet and modifies the vorticity field in regions with high density and pressure gradients. The present work is validated by comparing two types of cavitation surges observed experimentally in the literature with further interpretations based on simulations.     

A study on the characteristics of in-cylinder intake flow in spark ignition engine using the PIV

In this study, to investigate m-cyhnder tumble or swirl intake flow of a gasoline engine, the flow characteristics were examined with opening control valve (OCV) and several swirl control valves (SCV) which intensify intake flow through steady flow experiment, and also turbulent characteristics of m-cyhnder flow field were investigated by 2-frame cross-correlation particle image velocimetry (PIV) method In the investigation of intake turbulent characteristics using PIV method, the different flow characteristics were showed according to OCV or SCV figures The OCV or SCV installed engine had higher vorticity and turbulent kinetic energy than a baseline engine, especially around the wall and lower part of the cylinder Above all, SCV B type was superior to the others About energy dissipation and reynolds shear stress distribution, a baseline engine had larger loss than OCV or SCV installed one because flow impinged on the cylinder wall It should be concluded, from what has been said above, as swirl component was added to existing tumble flow adequately, it was confirmed that turbulent intenstty was enlarged, flow energy was conserved effectively through the experiment In other words, there is a suggestion that flow characteristics as these affected to m-cyhnder combustion positively     

Measurements of wall shear stress in horizontal air–water bubbly flows

The mean and time-varying fluctuation property of local wall shear stress of horizontal air–water bubbly flows in a circular pipe of 35 mm I.D. is measured using a TSI-1268W hot film probe. Data are collected in both entrance and developed regions of the flows. The variation of wall shear stress with L/D is analyzed, and the entrance length is determined to be 52–65 D at present studies. It is found that the wall shear stress is not uniform around the pipe circumference due to the asymmetrical phase distribution in the flows. The mean shear stress tends to decrease circumferentially from the pipe bottom to top. An increase of air flow rate at a constant water flow rate would further lower the wall shear stress at the upper part of the pipe and at the same time raise the wall shear stress at lower part of the pipe in both entrance and developed regions. An increase of water flow rate at a constant air flow rate would result in an increase of wall shear stress at all circumferential positions. The statistical property of wall shear stress is also discussed.     

磁力搅拌湍流场的PIV测量及流场演变的POD分析

为了解磁力搅拌过程湍流特性,对其开展了激光粒子图像测速(PIV)试验,并进行了本征正交分解(POD)分析.分析表明,在测量平面转子外部区域,除平均流动,含能量较高的流动结构为循环剪切流和转子旋转的尾涡结构.在搅拌槽底部具有较高的旋涡强度,有利于固体颗粒悬浮.流体与转子之间的流-固耦合作用使转子产生振荡,随转速升高,系统...