挖掘机用复杂结构排气消声器的CFD仿真研究

建立了某挖掘机用复杂结构排气消声器的仿真模型,并利用CFD技术对消声器某入口流速下的流场进行了仿真,分析了该消声器内部气体的流动特性及压力分布特性,通过追踪消声器内部气体的踪迹发现内部的漩涡产生了较大噪声及压力损失,随着入口气体流速的增大,消声器出入口压力及总体压力损失都呈类 似于抛物线的规律变化.研究了试验和仿真环境中,不同工况下消声器的压力损失,各种工况中,误差率在最低速时仅为5.5%,最高速时达到了20.5%,说明入口流速对于仿真结果有很大的影响.研究表明CFD方法研究消声器压力损失的有效性.     

3D flow past transonic turbine cascade SE 1050 — Experiment and numerical simulations

This paper is concerned with experimental and numerical research on 3D flow past prismatic turbine cascade SE1050 (known in QNET network as open test case SE1050). The primary goal was to assess the influence of the inlet velocity profile on the flow structures in the interblade channel and on the flow field parameters at the cascade exit and to compare these findings to results of numerical simulations. Investigations of 3D flow past the cascade with non-uniform inlet velocity profile were carried out both experimentally and numerically at subsonic (M 2is = 0.8) and at transonic (M 2is = 1.2) regime at design angle of incidence. Experimental data was obtained using a traversing device with a five-hole conical probe. Numerically, the 3D flow was simulated by open source code OpenFOAM and in-house code. Analyses of experimental data and CFD simulations have revealed the development of distinctive vortex structures resulting from non-uniform inlet velocity profile. Origin of these structures results in increased loss of kinetic energy and spanwise shift of kinetic energy loss coefficient distribution. Differences found between the subsonic and the transonic case confirm earlier findings available in the literature. Results of CFD and experiments agree reasonably well.     

带有冷气掺混的三级透平气动性能数值研究

借助NUMECA数值仿真软件,以某型燃气轮机的三级透平作为计算模型,对其在冷却气体掺混前后的流场进行了数值模拟。考虑到工质物性的影响,采用了变比热高温燃气作为计算工质。同时,针对燃气轮机透平进口的变工况问题,选取不同的透平进口总压值进行数值计算。结果表明,冷却气体的加入使得级损失增大,每列叶片流道出口速度或相对速度减小,下游叶片进口气流角减小;在三级透平冷气掺混时改变进口总压值,每列叶片流道的进口气流角几乎不变,除第三级动叶的激波损失与尾迹损失增大外,其余叶片流道的能量损失变化不明显。     

高负荷氦气压气机平面叶栅数值试验及叶型优化

基于大转折角基元级速度三角形设计概念,使用CFD软件对3种进气马赫数、6种进气角、3种扩压因子、3种叶栅稠度、2种叶型最大厚度比的共计324个平面叶栅流场进行数值计算。为了提高新型叶栅的性能,利用人工神经网络构建基于数据库样本空间的近似函数,采用遗传算法来寻找新的设计,并对新的设计进行气动性能预测。对中弧线和厚度分布进行优化,优化后总压损失系数降低了14.48%。     

最大厚度位置对高亚音轴流压气机叶型设计的影响

为了在具有不同负荷的压气机叶栅的初始设计过程中选取最大厚度位置,采用数值方法对在不同折转角的高亚音来流条件下对扩压叶栅进行了大量的系统性研究,分析了最大厚度位置、折转角以及稠度3个叶栅几何参数对叶栅变冲角特性以及对最小损失冲角下的叶栅气动性能的影响规律.基于大量叶栅样本建立数学模型,用来定量描述最小损失冲角,以及最小损...     

湿蒸汽非均质高速凝结流动的数值研究

基于冠状成核机理,建立了湿蒸汽两相非均质凝结流动数值模型,对缩放喷管、汽轮机叶栅和汽轮机级内湿蒸汽两相非均质凝结流动进行了数值模拟．结果表明：与自发凝结相比,非均质凝结流动中杂质颗粒改变了凝结过程;杂质颗粒减小了喷管中凝结激波强度,改变了汽轮机叶栅中的压力分布,降低了蒸汽过冷度,减少了不平衡热力学损失;在汽轮机级内,非均质凝结流动的动、静叶进、出口汽流角接近过热蒸汽流动的动、静叶进、出口汽流角,其动叶前压力高于过热蒸汽的动叶前压力,但级反动度偏离过热蒸汽流动数值．     

EFFECTS OF RAREFACTION AND COMPRESSIBILITY OF GASEOUS FLOW IN MICROCHANNEL USING DSMC

The direct simulation Monte Carlo (DSMC) is performed for two-dimensional gaseous flow through a microchannel in both slip and transition regimes to understand the effects of compressibility and rarefaction. Results are presented in the form of axial pressure distribution, velocity profile, local friction coefficient, and local Mach number (Ma) and are compared with the available analytical and experimental results. The effect of compressibility is examined for the inlet to outlet pressure ratios ranging from 1.38 to 4.5. Low-pressure drop simulations with Knudsen numbers (Kn) ranging from 0.03 to 0.11 are performed to identify the effect of rarefaction. It was found that compressibility makes the axial pressure variation nonlinear and enhances the local friction coefficient. On the other hand, rarefaction does not affect pressure distribution but causes the flow to slip at the wall and reduces the local friction coefficient. In addition, it was found that the locally fully developed (LFD) assumption is valid for low Ma flows by comparison with DSMC results.     

低流阻系数轴流式止回阀的内部流场分析

为了设计公称直径为DN200的低流阻系数轴流式止回阀,并准确分析其压力损失和流阻特性,在其原有的结构基础上,用汇源法设计止回阀的阀芯结构,得到结构优化后的轴流式止回阀。基于FLUENT(商用计算流体力学)软件提供的标准k-ε两方程湍流模型,对结构优化后的轴流式止回阀进行三维流道数值模拟,求解出不同工况下的压力云图和速度流线图,计算出优化后的止回阀流阻系数在0.272以下,小于优化前的0.4。最后,总结出进口压力、进口速度与流阻系数之间的关系。计算结果表明:在止回阀流道结构保持不变的情况下,影响止回阀流阻系数的主要因素是进口平均速度,随着进口流速的增大,止回阀的流阻系数呈逐渐减小的趋势;在进口速度保持不变的情况下,进口压力的变化对止回阀的流阻系数影响较小。     

An Experimental Study on 3—D Flow in an Annular Cascade of High Turning Angle Turbine Blades

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Effects of tangential velocity distribution on flow stability in a draft tube

Numerical simulations of the flow in the draft tube of a Francis turbine are carried out in order to elucidate the effects of tangential velocity on flow stability.Influence of the location of the maximum tangential velocity is explored considering the equality of the total energy at the inlet of the draft tube.It is found that the amplitude of the pressure fluctuation decreases when the location of the maximum of the tangential velocity moves from the centre to the wall on the cross section.Thus,the stability of the flow in the draft tube increases with the moving of the location of the maximum tangential velocity.However,the relative hydraulic loss increases and the recovery coefficient of the draft tube decreases slightly.     

Simulation and experimental measurements of 10-kW PEMFC passive hydrogen recovery system

Simulations are performed to examine the performance of a vacuum ejector in the hydrogen recovery loop of a 10-kW PEMFC system. The simulations commence by examining the effects of the primary flow fluid pressure and secondary flow temperature on the recirculation ratio and hydrogen stoichiometric ratio. Further simulations are then performed to investigate the temperature, pressure, velocity and Mach number distributions within the ejector for various values of the primary flow inlet pressure and temperature. A prototype ejector is fabricated using a 3D printing technique. Experiments are performed to evaluate the gas tightness and gas recovery performance of the ejector under realistic operating conditions. The simulation results show that the recirculation ratio and hydrogen stoichiometric ratio increase with a decreasing primary flow inlet pressure and secondary flow inlet temperature. As the primary flow inlet pressure increases, the pressure, velocity, and Mach number in the mixing chamber increase, and the hydrogen recovery performance decreases. Furthermore, as the temperature of the primary fluid flow increases, the stability of the isentropic flow condition within the ejector is enhanced. The experimental results show that the prototype vacuum ejector has a maximum gas leakage of just 0.7 psi and a minimum hydrogen recirculation rate of 59.3%. Consequently, it has significant potential for passive hydrogen recovery in large-scale fuel cell systems.     

空心静叶缝隙抽吸对蒸汽流场影响的数值研究

在缝隙抽吸条件下,采用Fluent软件对某600MW汽轮机末级空心静叶栅内的蒸汽流场进行了三维数值模拟,讨论了缝隙位置与结构参数对主蒸汽流场的影响。结果表明:随着缝隙位置从叶片前缘向叶片尾缘的移动,汽流总压损失系数逐渐减小。缝隙抽吸使叶栅进口马赫数有所升高,且内弧上的缝隙抽吸对马赫数的影响要大于背弧上的影响;当缝隙角度α=45°时,缝隙抽吸对叶栅进口马赫数的影响较大;缝隙宽度的增大使叶栅进口马赫数升高的幅度也越大。缝隙抽吸对叶片表面压力分布总体影响不大,仅在缝隙附近的汽流静压有较大的降低;随着缝隙宽度的增加,缝隙处的汽流静压降低越大。另外,缝隙抽吸使叶片表面的汽流边界层有所减薄。     

High-Frequency Pulsatile Pipe Flows Encompassing All Flow Regimes

Time-varying pipe flows driven by a harmonically pulsating inlet velocity and spanning all flow regimes have been investigated by means of numerical simulations. The Reynolds number varied from 1000 to 5000 in response to the inlet velocity oscillations. The frequency of the pulsations was varied from 1 to 10 Hz. These frequencies are markedly higher than those previously studied (maximum value of 0.025 Hz). The motivation for the use of the elevated frequency range was engendered by practical applications such as cardiovascular and respiratory systems of mammals in addition to numerous industrial applications. The simulations made use of the modified Menter transitional model. The key conclusion found here is that the use of a quasi-steady model for the prediction of fully developed friction factors is not applicable for the higher frequencies considered here. The deviations between the actual and quasi-steady friction factor values increase markedly with increasing frequency. Backflow occurs near the wall as the flow transists from deceleration to acceleration. This transition gives rise to a change in the sign of the axial pressure gradient. The amplitudes of the pressure oscillations generated by the imposed velocity variations increase markedly with increasing frequency and diminish with increasing downstream distance from the pipe inlet. The effect of modifications of the Menter model was assessed by carrying out separate numerical solutions for the unmodified and modified models. The pressure oscillations corresponding to the respective models were compared, and it was found that the deviations are insignificant.     

燃气轮机陆基试验台进气系统阻力模拟装置气动性能数值分析

为某型燃气轮机陆基试验台进气系统设计了一种由5个节流板组成的进气阻力模拟装置,用于模拟燃气轮机实船状态下的进气阻力。采用CFD数值模拟方法,分析该装置阻力模拟装置节流板不同偏转角度对燃气轮机进口空气流场及总压损失的影响,通过试验验证了数值模拟结果的准确性。数值结果表明：节流板顺时针持续偏转,下流底部回流区域逐渐扩大,下游主流流速分布较均匀,有利于燃气轮机运行;同时节流板偏转使得燃气轮机进口截面顶部区域低速区扩大,截面高速分布区域更加均匀。节流板逆时针偏转会增大燃气轮机进口截面不均匀度,且引起的总压损失要大于顺时针偏转,不利于燃气轮机运行。同时还通过试验验证了数值计算模型和相关分析的可靠性,为节流板的设计、安装提供了重要的理论依据。     

基于LES的压气机叶栅通道非定常流动结构研究

为了进一步理解压气机叶栅通道内的非定常流动结构,采用大涡模拟(LES)方法研究了来流附面层厚度和稠度变化对叶栅通道内涡系结构及总压损失系数的影响。研究表明：来流附面层增厚将导致端壁处流体的轴向动能降低,使得马蹄涡压力面分支更早地流向相邻叶片吸力面;来流附面层越厚,通道涡在叶栅尾缘沿展向抬升的高度越高,角区分离的范围也越大;叶栅的总压损失随附面层增厚而增加,附面层损失增加显著,二次流损失有所增大;稠度较低时叶栅吸力面表面存在分离,会对通道涡及角区分离产生影响;稠度增大,横向压力梯度减小,叶栅流道的速度分布更均匀,通道涡的强度和尺度减小,角区分离的范围减小;稠度增大使叶表不再分离时,总压损失显著降低,但稠度继续增大会使气流与叶片表面的摩擦损失增加。     

Effect of inlet box on performance of axial flow fans

Numerical investigations on 3D flow fields in an axial flow fan with and without an inlet box have been extensively conducted, focusing on the variation of fan performance caused by the internal flow fields and the velocity evenness at the exit of the inlet box. It is interesting to find that although the inlet box is well designed in accordance with basic design principles, there is a flow separation region in it. Furthermore, this flow separation and the resulting uneven velocity distribution at the exit lead to some decrease in the efficiency and an increase in the total pressure rise of the fan. This research shows that the inlet box needs further improvement and such a check on the flow fields is of value for the design of inlet boxes.     

Influences of inflow condition on non-axisymmetric flows in turbine exhaust hoods

The complex 3D flow in a steam turbine exhaust hood model with different inlet swirl and inlet total pressure radial distributions has been simulated by employing CFX-5 and analyzed in this paper. It＇s found that the inlet tangential flow angle at hub has a negative effect on the exhaust hood performance, while a negative gradient of inlet total pressure radial distribution has a positive impact on the hood performances. It＇s also numerically con- firmed that a proper distribution of total pressure at hood inlet can successfully eliminate the negative effects caused by the inappropriate inlet swirl distribution and improve the hood aerodynamic performance.     

Exergoeconomic analysis and optimization of basic,dual-pressure and dual-fluid ORCs and Kalina geothermal power plants: A comparative study

In present work, the basic, dual-pressure and dual-fluid ORCs and Kalina cycle for power generation from the geothermal fluid reservoir are compared from energy, exergy and exergoeconomic viewpoints. To do so, first thermodynamic models are applied to the considered cycles; then by developing cost flow rate balance and auxiliary equations using SPECO method for all components, the cost flow rate and unit cost of exergy for each stream are calculated. The results show that the turbine in basic and Kalina cycles and low pressure turbine in dual-pressure and dual-fluid ORCs have the maximum value of sum of total cost rate associated with exergy destruction and total capital investment cost rate. Thus, more attention should be paid for these components from the exergoeconomic viewpoint. The cycles are optimized to obtain maximum produced electrical power in the cycles as well as minimum unit cost of produced power. The optimization results show that among the considered cycles, dual-pressure ORC has the maximum value of produced electrical power. This is 15.22%, 35.09% and 43.48% more than the corresponding values for the basic ORC, dual-fluid ORC and Kalina cycle, respectively in optimal condition. Also Kalina cycle has the minimum value of unit cost of power produced and its value in optimum state is 26.23%%, 52.09% and 66.74% less than the corresponding values for the basic ORC, dual-pressure ORC and dual-fluid ORC, respectively in optimal condition. Finally a parametric study is carried out to assess the effects on thermodynamic and exergoeconomic parameters of the considered cycles of operating pressures and ammonia mass concentration.     

导叶开度对混流式水轮机转轮内部流态的影响

基于数值模拟方法,以梯级水光蓄互补联合发电系统示范工程中的猛固桥电站混流式水轮机为研究对象,对水轮机在不同特征水头、不同导叶开度工况下转轮叶片表面受力及流道内流场特性进行研究,分析导叶开度改变对水轮机转轮内流态的影响规律。结果表明：导叶开度对于混流式转轮进口流态的影响较大,导叶开度越小入流速度波动程度越大,来流对叶片头部冲击越大,在进口处产生严重的冲击损失;随导叶开度减小,转轮叶片表面等压线与进口边夹角增大,在上冠交接区域产生小三角区低压,使转轮流道出口更易产生空化损失。