交变流动中压力速度之间相位差对突变截面损失的影响分析

从弱非线性热声理论出发,给出交变流动中突变截面阻力系数的定义以及考察方法。通过PIV(粒子成像测速仪)测量与CFD计算结果的对比,验证了CFD计算结果的可靠性。进而利用CFD模拟考察了交变流动中压力与速度之间相位差对突变截面局部损失的影响,观察到产生这种影响的流场内部流动机制。分析表明,阻力特性确实对声场压力与速度之间的相位差存在依赖性,但这种依赖性会随着非线性的增强而减少。     

脉冲管制冷机变截面交变流动特性CFD研究

采用计算流体力学(CFD)方法,对小型脉冲管制冷机进行了二维数值模拟,研究了脉冲管制冷机部件变截面处的结构非对称性对流场的影响。数值模拟结果观测到由非对称结构所引起的非对称流动,揭示了第三直流效应的产生机理,这种非对称流动以周期性演变的涡量环流的形式进行。涡量环流的演变是一个能量的耗散过程,文中还对比了不同输入功率和运行频率对涡量耗散的影响。此外,将数值模拟结果与实验实测结果进行对比,验证了数值模拟的有效性,并从涡量耗散的观点出发对小型脉冲管制冷机输入功率增加到一定程度后制冷温度升高的反常现象进行了解释。     

惯性项对回热器交变流动阻力特性影响分析

基于流体动量方程从机理上分析了交变流动和稳定流动存在差别的根本原因。以动态参数测量为基础,在运行频率30～60 Hz,最大热端压比1.3,充气压力1.0～3.0 MPa,等温条件下,首次定量化研究了惯性项对小管径(φ8 mm)、高目数丝网(300～500目)填充回热器交变流动阻力特性的影响。综合频率和压比对交变流动回热器阻力特性的影响,可以得出结论:在本实验条件下,回热器交变流动系统中的惯性力与压力相比始终是个小量,从流动角度来说,可以对回热器中气体交变流动作准稳态处理。     

热声交变流动中浮力效应理论分析

热声交变流动是热声热机的工作基础,研究交变流动机理有助于人们认识热声热机的工作过程。鉴于前人的理论分析一般没有考虑浮力效应的影响,本文从流体热动力学的角度研究了浮力对流与热声交变流动的耦合规律。基于线性理论方法,给出了考虑浮力项和热对流Rayleigh数的热声线性理论模型,分析了浮力效应对平行交变流动的影响,发现热对流...     

芯片微通道沸腾相变过程中流动交变现象探析

亚微米芯片通道中的沸腾相变极不稳定,在某些条件下,在芯片微通道的同一位置处会出现不同相态流体的交变现象,并伴随有剧烈的热力参数波动。本文通过显微观测和高速摄影技术,对芯片微通道沸腾相变过程中不同相态流体交变现象的成因及特点进行了揭示和分析,这对认识高热流密度条件下芯片微热沉中的流动非稳定性问题具有重要意义。     

交变流动下间隙密封耦合气体轴承的特性研究

气体轴承是回热式热机的一项关键技术,它是利用气体代替润滑油作为润滑剂,在轴与轴承套之间构成气膜,是避免运动面与静止面直接接触的较为理想支撑元件.将间隙密封与气体轴承相结合,可以在实现密封的同时消除接触磨损.本文利用ANSYS Fluent对具有77 kW(声功)设计输出能力的活塞进行其气体轴承与间隙密封耦合特性的数值模...     

细小圆管内液体流动特性实验研究

本文实验研究了去离子水在直径为 1.0～2.0 mm 的细小圆管中的流动阻力特性.通过比较相同直径、不同管长的压差,获得了摩擦因子及局部损失系数随 Re 数变化关系.本文实验条件下,对于不同直径的细小圆管,沿程压降及局部压降随流速变化趋势一致;随着管径减小,摩擦因子也减小,且在层流区和湍流区内均要比常规尺度条件下的小;对于不同直径的细小圆管,局部损失系数随 Re 数变化趋势基本一致,当 Re 数相同时,管径越小,对应的局部损失系数越大;对于直径为 1.0～2.0 mm 的细小圆管,临界雷诺数 Rec=2050～2300.     

结构参数对波纹管内液氮流动与能量损失的影响

高温超导电缆通常浸泡在采用真空多层绝热保护的双层波纹管内程管的液氮中。液氮在超导电缆内流动的压力损失和冷却效果是其运行系统设计的重要参数。对不同直径的波纹管进行了不同流量下的CFD仿真计算,结果表明流量越大、直径越小,压降越大;波高直径比与波高波距比不变时,波纹管的达西流动阻力系数与波纹管的直径基本无关;波纹管直径对超导电缆的沿程温升几乎没有影响;增大波纹管的直径能够大幅降低超导电缆的沿程能量损耗。该文结果为超导电缆设计过程中波纹管的选取提供了理论依据。     

变截面微石英管内流动特性分析

以去离子水作为工质,流经内径分别为304.13 μm和192.87 μm的石英管所连接而成的变径微管道,根据压降与流量的变化关系,研究微管道内过流截面突然扩大和缩小时微管内阻力特性.利用常规管路阻力损失计算方法对管路的阻力进行计算,并与实验值相比较.研究表明,当雷诺数Re(大直径微管)低于500时,微尺度变截面管路流阻的实验值近似等于常规管路阻力计算公式的计算值;当Re数大于500时,实验值与理论值产生偏差,并且随着雷诺数的进一步增大两者偏差越来越大.     

轴类转静间隙内CO2流动特性及摩擦损失研究

采用数值方法研究了CO2在轴类间隙内的摩擦损失和流动特性,分析了转子转速、CO2状态及几何尺寸对流动特性和损失的影响,并在Bilgen模型的基础上修正了摩擦损失模型.结果表明,数值计算结果与Bilgen模型预测结果之间的最大相对偏差为14.65％,与Vrancik、Yamada模型之间的最大相对偏差分别为219.37％...     

基于VLES模型的振动圆柱数值模拟

本文将一种VLES(Very Large Eddy Simulation)模型引入到动网格数值计算中,并验证了VLES模型用于模拟类似振动圆柱绕流的动边界问题的有效性.数值求解了不同振幅和频率下非稳态振动圆柱绕流问题.研究表明:随着振幅和激励频率的增加,绕圆柱流动涡脱离形式从2S模式转换到2P0模式,再到P+S模式.在...     

Internal Flow Patterns on Heat Transfer Performance of a Closed-Loop Oscillating Heat Pipe with Check Valves

This article presents the experimental results of an evaluation of the influence of internal flow patterns on the heat transfer performance of a closed-loop oscillating heat pipe with check valves. It was found that the internal flow patterns could be classified according to four flow patterns: dispersed bubble flow, bubble flow, slug flow, and annular flow, respectively. The main regime of each flow pattern can be determined from a flow pattern map. The map can be used to predict the trend of the heat transfer rate in the closed-loop oscillating heat pipe with check valves.     

多孔介质内交变流动与换热的格子Boltzmann研究

针对制约脉冲管制冷机效率提高的蓄冷器内交变流动与换热问题,本文使用格子Boltzmann方法计算并分析了多孔介质内交变流动与换热特性。结果表明,交变流动压力波振幅对速度与压力和温度间的相位差的影响很小;通道界面处速度与压力的相位差在某一孔隙率下有一极小值;多孔介质内最大阻力系数与雷诺数的关系可以为设计蓄冷器时填料结构的...     

飞秒钛宝石激光器腔内双色镜反射相移的突变现象

研究了钛宝石激光器增益介质两端的两块双色镜的相移色散，发现反射相移在中心波长附近发生了突变，由此而造成反射相移色散在此点是不连续的，并对影响反射相移突变点的因素进行了详细的研究。     

超临界二氧化碳在突扩管中对流换热的流动特性研究

对流动分岔后的超临界二氧化碳在平面对称突扩管中进行强迫对流换热进行了数值模拟,研究了热流密度在流体发生流动分岔现象后流动特性的影响。计算结果表明:随着热流密度的增加,临界雷诺数和转换雷诺数减小,流动稳定性遭到削弱;对应于相同的雷诺数,由于流动分岔引起的不对称压力分布随着热流密度的增加对应于突扩管上、下半部有不同变化规律,这使得对应回流区的大小分别减小和增大。     

Flow structure of the entrance of a T-junction duct without/with a circular cylinder

The flow characteristics of the trailing edge of vertical vanes installed at the intersection of a T-junction duct were experimentally investigated using particle image velocimetry. The measured velocity field in the branch duct with/without single circular cylinder was studied under different cross velocities and velocity ratios. Additionally, the effect of the locations of cylinder on the flow field was discussed. The positive velocity region, the unsteady flow region and the trailing edge flow region of the vane, have been observed. The positive velocity region existed in almost one half of the measured area. As for the unsteady flow region, the unstable double-vortex structure transformed into a single-vortex structure as the velocity ratio increased. As for the trailing edge flow region of the vanes, the vortex streets could be visualised. Furthermore, the location of cylinder has revealed significant influence on the flow distributions in the trailing edge flow regions of the vanes. The flow structure without cylinder in the measured area is dependent on combinations of the cross velocity and velocity ratio, whereas that with cylinder is dependent on the velocity ratio. The vorticity fields were analysed in each region, and the velocity components revealed the cause of airflow trajectory.     

Experimental Study of Flow Through a Blade Trailing Edge with a Wavy Partition

Abstract

Flow through a blade trailing edge passage has been experimentally investigated in this article. This rectangular passage is divided into two channels by either a straight or a 120° wavy partition. Fluid in the first channel was injected into the second channel via 14 openings (holes) distributed uniformly and in the crests and troughs for the wavy configuration. Particle image velocimetry and a charge coupled device camera were used in experiment, with Reynolds number varying from 1,800 to 6,700. Experimental results show that the wavy configuration produces an oscillation flow in the second channel. The cause for the oscillation may due to the 120° wavy partition causing shear-layer instabilities and the formation of spanwise eddies by the wavy board. Pictures from the charge coupled device camera revealed strong mixing in the trailing edge, and this mixing could enhance heat transfer, which was confirmed in previous research. The amplitude of oscillation depends on Reynolds number and hole positions. It was observed that the injection flow was not symmetric to the openings, and it was skewed to the direction of the first channel main flow. The ratio of flow rate through the outlet and the bleeding holes was from 1:1 to 1:3.     

气固两相槽道湍流拟序结构变动的PIV测量

运用粒子成像测速仪(PIV)对壁面雷诺数为Re_τ=430、质量载荷为0.25×10~(-3)～5×10~(-3)的110μm聚乙烯颗粒加入前后的水平槽道湍流变动进行了研究。实验结果表明低载荷下气相湍流变动源于颗粒对湍流拟序结构的作用。颗粒的存在抑制了湍流拟序结构的发展,使得湍流准流向结构长度减小、猝发频率降低、猝发强度减弱;另外,颗粒尾涡脱落还导致了壁面附近的气相剪切雷诺应力增强。