整体涡旋流畸变对轴流-离心组合式压气机喘振特性影响的数值研究

为研究整体涡旋流畸变对轴流-离心组合式压气机喘振特性的影响，本文采用气腔模型来研究压气机出口的容腔效应，分别模拟了均匀进气以及不同旋流强度的正向及负向整体涡旋流畸变作用下，组合式压气机的喘振过程。研究发现，正向整体涡旋流畸变作用下，离心叶轮进口截面近盘侧存在强度较大、范围较广的正向旋流，一定程度上抑制了叶轮内的流动分离；相反地，负向整体涡旋流畸变作用下，离心叶轮进口截面近盘侧存在强度较大、范围较广的负向旋流，使叶轮内的流动分离加剧甚至引发回流，使得压气机系统进入深度喘振工况。正向整体涡旋流畸变的旋流强度越大，组合式压气机的喘振圈及喘振频率越小；负向整体涡旋流畸变作用下，旋流强度越大，喘振圈越大、喘振频率越高。     

粉煤气化炉喷嘴旋流数对炉内流场及燃烧特性的影响

对带旋流单喷嘴粉煤加压气化炉内多相燃烧流场,建立二维旋流对称模型进行数值模拟。计算采用涡耗散概念模型,同时考虑体积反应和焦炭表面反应,模拟多机理的湍流燃烧。通过改变喷嘴内部旋流数进行平行模拟,研究不同旋流数下炉内流场的回流分布特性以及火焰的形态和分布等燃烧特性。结果表明:带有旋流喷嘴的气化炉,炉内流场分布主要由中心回流区和外回流区的旋流涡构成;旋流数增大导致轴向速度衰减加快,延长了粉煤颗粒在炉内停留时间,但旋流过大会导致颗粒在炉顶聚集形成"死区";旋流数S≤1.2时,火焰为锥子状,炉内整体高温不利于气化反应;旋流数S≥1.6时,炉内高温区上移至炉顶,火焰呈扁平花瓣状,扩散角过大容易形成回火;通过拟合高斯曲线得到本气化炉最佳旋流数为1.4。     

液压油箱用固液旋流分离器分离效率影响规律

颗粒物污染是影响移动装备液压元件及系统性能的主要原因之一,液压油箱考虑去除杂质功能会增加其设计容积,不利于液压系统轻量化设计。应用离心分离的原理,使不同密度的介质在高速旋转的流场中进行分级筛选,可快速去除液压油中大颗粒污染物,提高液压系统可靠性,提升过滤器使用寿命。由于旋流分离器中流场的流动形式复杂,预测旋流分离器内部的流场特性、颗粒运动轨迹十分困难。因此,研究旋流分离器流场流动规律和污染物旋流分离机理,可以为液压系统污染物分离和去除提供理论基础。针对固液旋流分离器的流场分布规律和污染物分离效率的影响规律展开研究。根据旋流分离理论设计了固液旋流分离器结构,分析旋流分离器不同直径和长度下,固液旋流分离器轴向速度、切向速度的分布规律,通过粒子图像测速法对仿真结果进行试验验证,得到结构参数对分离效率的影响规律。结果表明,当中心的轴向速度为负值、壁面附近的轴向速度为正值时,切向速度越大,越有利于分离液压油中的颗粒。该研究结果可对液压油箱用固液旋流分离器的结构设计提供理论指导。     

进口旋流条件下径流涡轮性能异化机制研究

可调两级增压系统中的低压级涡轮受高压级涡轮及上游管道的影响，其进口流场存在较强的旋流，进而该涡轮性能较均匀直流进气条件时呈显著异化现象。针对该问题，本文基于旋流发生器手段，开展进口旋流条件对径流涡轮性能影响的机制研究。结果表明，旋流改变了涡轮进口处的流场分布形态，并在蜗壳通道内产生周向畸变，从而改变周向上各叶轮进口的气流分布，造成蜗壳和叶轮内的显著流动损失异化。随着旋流强度的增大，涡轮效率的下降幅度越大，最大下降约4.1%。该研究探明了不同进口旋流条件下径流涡轮性能的异化机制，为两级可调增压系统高效涡轮设计提供了理论参考。     

中心给粉旋流燃烧器气固两相流动的数值模拟

电厂采用的煤粉燃烧技术应达到稳燃、低污染、防结渣及防高温腐蚀的要求。中国电厂燃用煤的煤质偏差,煤种多变。在燃用这些煤的时候,锅炉的稳燃能力较低。针对这些问题,提出中心给粉旋流煤粉燃烧技术。由于燃烧器的气固流动特性对燃烧器的性能有很大的影响,利用可实现的k-ε和Lagrangian随机轨道模型对中心给粉旋流燃烧器的气固两相流动进行数值模拟,并将计算结果和三维相位多普勒测速技术(Phase-Doppler anemometry,PDA)试验结果进行详细比较,计算值和试验值速度分布的趋势基本相同。计算和试验结果表明,在轴向方向产生了回流区,切向速度分布出现典型的Rankine涡结构,中心线附近区域的径向速度小。当颗粒的轴向速度衰减为0之后,颗粒的运动方向发生偏转,开始向后上方运动。颗粒迂回型运动轨迹延长了煤粉在回流区中的停留时间。     

叶片式旋流发生器的设计与数值计算

应用NACA65系列叶型,设计了一套叶片式旋流发生器.利用CFD计算,对旋流发生器进行了各种可调参数组合的数值计算,分析了可调参数对旋流发生结果的影响.数值计算结果表明:所设计的旋流发生器能够产生整体涡强度达(8～22).的旋流;叶片数对旋流整体涡强度的影响最为显著.     

基于CFD的轴向柱塞泵腔道设计优化

该文以XB01VSO轴向柱塞泵腔道为研究对象,分析轴向柱塞泵腔道内的压力分布、速度特性等。轴向柱塞泵的腔道形状和方向变化决定了油液的流动状态,腔道的设计不合理会产生旋涡,造成油液回流,产生振动和噪声~[1]。通过应用ANSYS CFX软件仿真分析结果,对轴向柱塞泵腔道进行优化改进,为轴向柱塞泵腔道的设计提供参考。     

混流泵启动过程进口流动特性的数值模拟

通过建立包括叶轮、导叶、蜗壳、阀门、稳压罐及管路在内的全三维闭合回路模型对混流泵启动过程进行数值模拟,分析了启动过程进口回流的形态及形成原因,研究了回流的轴向长度、轴向速度和圆周速度的分布以及轴向截面回流量、回流面积的变化。研究结果表明,数值模拟与试验结果基本一致,数值计算方法较为可靠。叶片吸力面的流动分离和叶顶间隙泄漏是造成进口回流的主要因素。启动过程中的回流参数均随时间呈现先增大后减小的趋势,主流与回流轴向速度在启动初期呈现对称分布,0.8 s后的回流轴向速度出现非对称分布且离叶轮进口越远非对称分布越明显;受回流排挤,主流轴向速度分布在不同截面呈现不同变化趋势,圆周速度逐渐呈非对称分布,进口管圆截面处平面速度方向逐渐偏离圆周切向,各轴向截面处回流量、回流面积的变化趋势基本一致,每个截面相继出现一个回流面积极大值。     

流场转速对旋流分离性能影响研究

应用欧拉-拉格朗日方法,对双锥型液-液分离旋流器内不同入口速度条件下的分离性能进行数值模拟及试验,得出随着旋流场转速的逐渐增大,旋流分离效率逐渐升高。为研究旋流分离过程中不同流场转速对分离性能的影响因素,采用粒子成像测速技术(PIV)对旋流样机内部速度场进行测量试验,并采用高速摄像技术记录了变转速旋流场内离散相分离过程。结果表明:流场转速对旋流分离性能的影响除离心力外,还受到轴向截面上二次衍生涡流数量及分离过程中油核摆动幅度的影响;本文研究的旋流结构内随着流场雷诺数的增加,轴向截面上二次衍生涡流数量逐渐减少。当雷诺数Re≥2.51×10~5时,可以忽略轴向截面上二次衍生涡流对分离性能产生的不利影响;旋流分离过程中流场低转速旋转时油核摆动幅度较大,使离散相分离轨迹发生偏移,使旋流分离性能降低。测量范围内油核摆动最大幅值像素坐标差为100,在t=5.2 s后油核摆动幅值为0,此时可以忽略油核摆动对旋流分离性能的不利影响。     

旋流风口的数值模拟与试验研究

旋流风口的形状较为复杂,其建模情况影响着室内流场和室内自净时间。为了研究旋流风口的入流条件对室内流场的影响,对真实和简化的旋流风口物理模型进行数值模拟,并对采用旋流风口送风时的室内温度分布和CO2浓度进行试验测试,从而验证旋流风口物理模型建模方法的正确性。研究结果表明,合理给出轴向速度和切向速度的简化物理模型,可以准确的模拟旋流风口的室内流场,这样就不用花费大量的计算资源去计算真实的物理模型。     

An investigation into the performance and diagnostics from different chordal integration schemes in asymmetric flow

The purpose of the work is firstly to explore the proposal from a previous North Sea Flow Measurement Workshop paper that increasing the number of chordal locations above 4 yields little improvement in the performance of ultrasonic flow meters. Secondly the work examines the relationship between profile factor and symmetry on theoretical velocity profiles and how that changes with an increased number of chordal locations. Finally, the benefits of more paths for the purposes of swirl cancellation are reviewed, particularly when axial asymmetry and swirl are present concurrently.It is found that in the presence of axial asymmetry there is a significant performance improvement to be had with an increased number of chordal locations.A relationship between profile factor and error is also apparent. The interpolation polynomial and weight function are used to visualise the quadrature and explain the correlation. The theory that more chordal locations will improve the correlation between error and profile factor is investigated, however initial results suggest this is not true.The theory behind swirl cancellation is explained and the velocity profile diagnostics of common designs in the presence of swirl and axial asymmetry are shown. Examples of how the user can be fooled into thinking all is well in the presence of both axial asymmetry and swirl are also shown. The sensitivity of some designs to swirl is also examined.The modelling suggests that in cases where swirl and axial asymmetry are present together and non-axial velocity components are not removed by swirl cancellation or flow conditioners, a change in traditional velocity profile diagnostics cannot be used to indicate the magnitude of the error.     

涡轮流量传感器在旋转来流中的特性研究

本文对涡轮流量传感器在旋转来流中的特性进行了理论和实验研究。利用涡轮流量传感器的数学模型,给出了涡轮转速、仪表常数与来流旋转角之间的理论关系式。计算了来流旋转强度及上游直管段长度变化时,仪表常数的变化情况。设计了能获得不同来流旋转强度的旋转发生器,并获得了大量的实验数据。实验结果与理论计算值在较大的流量范围内甚为吻合。     

Investigation of the three-dimensional turbulent flow fields of the gas swirl burner with a cone type baffle plate (I)

This paper presents vector fields, three dimensional mean velocities, turbulent intensities, turbulent kinetic energy and Reynolds shear stresses measured in the X-Y plane of the gas swirl burner with a cone type baffle plate by using an X-type hot-wire probe. This experiment is carried out at the flow rates of 350 and 450 ℓ/min which are equivalent to the combustion air flow rate necessary to release 15,000 kcal/hr in a gas furnace. The results show that the maximum axial mean velocity component exists around the narrow slits situated radially on the edge of a burner. Therefore, there is some entrainment of ambient air in the outer region of a burner. The maximum values of turbulent intensities occur around the narrow slits and in front of a burner up to X/R=1.5. Moreover, the turbulent intensity components show a relatively large value in the inner region due to the flow diffusion and mixing processes between the inclined baffle plate and the swirl vane. Consequently, the combustion reaction is expected to occur actively near these regions.     

径向水平井自进式旋转射流钻头流场特性分析

为解决径向水平井钻进过程中破岩效率和自进能力的问题,设计了一种自进式旋转射流钻头。运用数值模拟方法,采用RNG k-ε湍流模型对所设计射流钻头的内外流场进行了三维流动特性分析,并分析了射流钻头结构参数对喷嘴流场特性的影响规律,进一步优化了自进式旋转射流钻头。结果表明,自进式旋转射流喷嘴外流场的轴心速度在喷嘴中心线上的速度最大,随着径向半径的增大,轴向速度迅速减小;切向速度沿喷嘴径向呈现出经典的"N"形分布,有利于增大射流破碎岩石的深度和破碎面积;径向速度呈轴对称分布,存在明显的漫流层,有助于岩屑的脱离;自进式旋转射流钻头导向叶轮的螺距和导叶数量,对射流速度有着重要的影响;喷嘴直径对射流流场特性的影响较大。经过优化,得到射流钻头的叶轮螺距16mm,导叶数为2,喷嘴直径为1mm。     

Measurements of Non-reacting and Reacting Flow Fields of a Liquid Swirl Flame Burner

The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device.Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a2-D particle imaging velocimetry(PIV)system.The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions,i.e.,with and without the combustor wall.The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions.The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume.The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow.Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet,where the radial velocity components increase for both open and confined environment.Under reacting condition,the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity.The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants.The flow field data can be used as validation target for swirl combustion modelling.     

管内螺旋导流板引发的气液两相旋流场

用数值模拟的方法研究某种螺旋导流板结构引发的管内气液两相旋流的流动特点。空气为主相,水为次相,入口为雾状流。研究旋转给流型转变、气液相分布、速度分布及旋流衰减带来的影响。发现雾状流在螺旋导流板的作用下,转变为环状流。螺旋导流板内有二次涡的生成,且二次涡结构不断发展变化,离心力分布不均匀而形成沿管壁周向不连续的液膜;流出螺旋导流板后,二次涡会衰减消失,流体做螺旋向前运动,液膜沿圆管周向逐渐分布均匀。管中心处气相切向速度小,气相切向速度较大的区域远离旋流中心区,旋流中心与圆管中心存在小的偏心距;与直管及螺旋纽带相比,螺旋导流板引发的气液两相旋流在圆管中心的气相轴向流速远高于光管和螺旋纽带;与螺旋纽带相比,螺旋导流板引发的旋流强度更大且衰减减慢。     

An investigation of swirling flow in a cylindrical tube

An experimental study was performed for measuring velocity and turbulence intensity in a circular tube for Re=10,000, 15,000 and 20,000, with swirl and without swirling flow. The velocity fields were measured using PIV techniques and swirl motion was produced by a tangential inlet condition. Some preliminary measurements indicated that over the first 4 diameter, two regions of flow reversal were set up (the so called 2-cell structure). At the highest Reynolds numbers, the maximum values of the measured axial velocity components had moved toward the test tube wall and produce more flow reversal at the corner of the tube. As the Reynolds number increased, the turbulence intensity of swirling flow at the tube inlet also increased.     

化工轴流泵的非均匀导叶布置

化工轴流泵的工作介质特性使其不便设置导轴承,导致泵转轴缩短,叶轮出口至弯管进口之间只有一段很短的垂直空间,在该空间采用常规导叶布置会恶化水力性能,而化工泵中通常不设置导叶的做法又会使叶轮出口圆周速度分量对应的能量在流道中逐渐损耗。为提高机组效率,采用计算流体力学(CFD)方法分析了均匀布置导叶时的流场特点,发现导致水力性能恶化的原因,提出非均匀导叶布置方案,并进行了数值模拟及对比。结果表明,合理的非均匀导叶布置方案能有效改善装置水力性能。     

An experimental study on swirling flow behind a round cylinder in the horizontal circular tube

An experimental study is performed for turbulent swirling flow behind a circular cylinder using 2-D PIV technique. The Reynolds number investigated are 10,000, 15,000, 20,000 and 25,000. The mean velocity vector, time mean axial velocity, turbulence intensity, kinetic energy and Reynolds shear stress behind the cylinder are measured before and behind the round cylinder along the test tube. A comparison is included with non swirl flow behind a circular and square cylinder. The recirculation zones are showed asymmetric profiles.