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针对一跨音速压气机转子,分别在动叶顶部相对间隙为0%,0.1%,0.5%,1%,1.5%,2%的六种情况进行了数值模拟。计算结果表明,间隙的存在使得转子性能如压比、效率有所下降,但适当间隙的存在使得转子喘振点往小流量点大幅迁移,又有效提升了转子的工作范围。此外,分析了由于叶顶间隙的存在使得转子工作范围增加的原因,并指出无论是否存在间隙,针对跨音速压气机转子,其进入喘振的根本原因都是由于堵塞作用使得弓形激波连同流道激波一起被推向流道上游造成的,而其中堵塞作用却是由端壁附面层发展与迁徙、叶顶泄漏流动、激波与附面层之间相互作用的共同结果。 相似文献
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离心压气机机匣处理与导叶轮缘放气的扩稳机理分析及比较 总被引:3,自引:0,他引:3
采用数值模拟方法对导叶轮缘放气、进气回流及周向槽机匣处理扩大离心压气机稳定工作范围进行研究,并与实壁机匣离心压气机特性进行对比,分析三种处理方式扩大压气机稳定工作范围的机理。结果表明,导叶顶部吸力面分离流动和间隙泄漏流相互作用导致压气机失速。导叶轮缘放气将吸力面分离流动产生的低能流团吸除,减弱了顶部通道堵塞。进气回流给顶部进气添加负预旋,减小了顶部来流攻角,能抑制吸力面流动分离。周向槽机匣处理减弱了顶部间隙泄漏向叶轮进口的回流。三种处理方式都能减弱顶部通道堵塞、推迟压气机失速发生,而进气回流和导叶轮缘放气具有较大的扩稳能力。 相似文献
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叶尖泄漏流动对航空发动机的压气机性能有很大的影响,对其进行准确的数值模拟十分重要。延迟脱落涡模拟(DDES)方法在保证计算准确性的同时节省了计算资源。本文针对不同间隙大小和不同工况对大尺寸低速轴流压气机转子进行了DDES模拟。将时均结果与瞬时结果进行了比较,分析了不同叶尖尺寸下流动的非定常性。然后利用LUMLEY三角形分析了叶尖泄漏流动的雷诺应力各向异性。各向异性沿叶尖泄漏涡向下游发展方向变化。小间隙情况下各向异性较弱,这是由于小间隙情况下流动更加稳定。最后,利用快速傅里叶变换(FFT)分析了泄漏涡核心的速度脉动频谱,讨论了泄漏流动的非定常性。 相似文献
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采用一种快速求解三维黏性流场的计算方法求解某离心压气机内部复杂的流场,该方法利用Denton J.D.教授的粘性体积力法模拟粘性对叶轮机械内部流动的影响,采用时间推进法和有限体积差分格式对叶轮机械内部的流动进行求解。为加速收敛,使用了多重网格法,当地时间步长和局部残差光顺技术。对某离心压气机内部流动进行了详细的数值模拟,得出了压气机转子性能、叶顶周向平均静压以及准正交面上子午速度分布图,计算结果与试验结果吻合良好。采用该方法详细分析了不同工况下离心压气机内部流场。 相似文献
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Numerical study on unsteadiness of tip clearance flow and performance prediction of axial compressor
Numerical calculations were performed to investigate unsteady features of tip clearance leakage flow in an axial compressor. The first stage rotor of a low speed axial compressor with a large tip clearance was examined. It was confirmed that the numerically calculated performance data were in good agreement with the experimentally measured performance data. Using frequency analysis, the flow characteristic near the casing induced by tip clearance leakage flow was found to be not associated with the rotating speed of the rotor. This characteristic is called rotating instability or self-induced unsteadiness. We found that the circumferential length scale of the rotating instability of the compressor was longer than a pitch of a blade passage; therefore, a multi-blade passage was adopted to study the flow structure more precisely. The flow characteristic was described by the frequency, the circumferential length, and the phase velocity, and was changed by operating points toward stall. The behavior of the flow was characterized by circumferentially traveling waves. Hence, the mechanism governing the development of the unsteady feature was further examined in terms of the rotating wave pattern of the pressure distribution. Furthermore, the unsteady feature of the tip clearance leakage flow affected the prediction of compressor performance by altering blockage, flow turning, and loss near the casing. 相似文献
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Time-accurate numerical calculations were performed to investigate unsteady flow features in a low-speed axial compressor. The test compressor has axial skewed slots over the rotor tip region as casing treatment to improve the stall margin. The calculated data are in good agreement with the measured data. This paper reports the effect of casing treatment and flow unsteadiness on the rotor near stall by examining the flows in the smooth wall and casing treatment cases. The axial skewed slot can remove the blockage induced by the tip clearance leakage flow by removing and injecting the flow near the tip. However, for the casing treatment case, blockage is induced near the hub because the hub-corner stall is caused by a decrease in the axial momentum in this region. The tip leakage flow has inherent unsteadiness in the smooth wall case caused by the relatively large tip clearance, whereas the hub-corner stall has unsteadiness in the casing treatment case. The two types of unsteadiness have functions in inducing stall inception. Furthermore, axial slots of different sizes were tested to examine the effect of slot geometry on rotor flow stability. The change in flow structure related to the stall inception was subject to flow injection through the recirculation in the slots. 相似文献
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叶轮是离心风机的核心部件,由于叶轮是高速旋转的部件,动静之间不能有接触,同时动静之间的间隙通过泄漏损失和二次流损失直接影响风机的效率。为有效地控制叶轮和形环之间的间隙,本文提出在叶轮轮盘侧添加凸台结构,采用4种改进设计方案。利用通用有限元分析软件ANSYS进行计算分析[1-3],综合考虑叶轮应力、应变等因素,最终得到了在新型设计方法下的最优设计方案。结果表明,新型设计改进方案有效地减小了叶轮的轴向位移量和径向位移量,为叶轮和形环之间的间隙设计提供了依据,进而可以最大限度地减少漏气损失和二次流损失。 相似文献
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LI Yang OUYANG Hua DU Zhaohui School of Mechanical Engineering Shanghai Jiaotong University Shanghai China 《机械工程学报(英文版)》2007,20(2):82-87
In the steady operation condition,the experiments and the numerical simulations are used to investigate the tip leakage flow fields in three low pressure axial flow fans with three kinds of circumferential skewed rotors,including the radial rotor,the forward-skewed rotor and the back-ward-skewed rotor. The three-dimensional viscous flow fields of the fans are computed. In the ex-periments,the two-dimensional plane particle image velocimetry (PIV) system is used to measure the flow fields in the tip region of three different pitchwise positions of each fan. The results show that the computational results agree well with the experimental data in the flow field of the tip region of each fan. The tip leakage vortex core segments based on method of the eigenmode analysis can dis-play clearly some characteristics of the tip leakage vortex,such as the origination position of tip leak-age vortex,the development of vortex strength,and so on. Compared with the radial rotor,the other two skewed rotors can increase the stability of the tip leakage vortex and the increment in the for-ward-skewed rotor is more than that in the backward-skewed one. Among the tip leakage vortices of the three rotors,the velocity of the vortex in the forward-skewed rotor is the highest in the circumfer-ential direction and the lowest in the axial direction. 相似文献
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为了研究在高速高压工况下双圆弧螺旋齿轮泵齿顶间隙对齿轮泵泄漏及空化特性的影响,建立了双圆弧螺旋齿轮泵最佳齿顶间隙数学模型,计算出最佳齿顶间隙。利用PumpLinx对考虑空化后不同齿顶间隙的齿轮泵内部流场进行数值模拟,结果表明:当齿顶间隙为0.02 mm,齿轮泵的流量脉动和压力脉动相对较小,流量输出品质好,与理论分析最佳齿顶间隙为0.0207 mm基本一致,验证了最佳齿顶间隙模型建立的正确性;齿顶间隙会影响齿轮泵内部流场的空化程度和泄漏量,齿轮泵内部的空化程度随着齿顶间隙的增大而减小,齿顶间隙处的泄漏会随齿顶间隙的增大而增大;齿轮泵齿顶间隙处的空化具有密封作用,可以减小齿顶间隙泄漏。研究结果对双圆弧螺旋齿轮泵结构优化及应用具有一定的参考价值。 相似文献
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Eum Hark-Jin Kang Young-Seok Kang Shin-Hyoung 《Journal of Mechanical Science and Technology》2004,18(6):979-989
Numerical simulations have been performed to investigate tip clearance effect on through-flow and performance of a centrifugal
compressor which has the same configuration of impeller with six different tip clearances. Secondary flow and loss distribution
have been surveyed to understand the flow mechanism due to the tip clearance. Tip leakage flow strongly interacts with mainstream
flow and considerably changes the secondary flow and the loss distribution inside the impeller passage. A method has been
described to quantitatively estimate the tip clearance effect on the performance drop and the efficiency drop. The tip clearance
has caused specific work reduction and additional entropy generation. The former, which is called inviscid loss, is independent
of any internal loss and the latter, which is called viscous loss, is dependent on every loss in the flow passage. Two components
equally affected the performance drop as the tip clearances were small, while the efficiency drop was influenced by the viscous
component alone. The additional entropy generation was modeled with all the kinetic energy of the tip leakage flow. Therefore,
the present paper can provide how to quantitatively estimate the tip clearance effect on the performance and efficiency. 相似文献
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Effect of honeycomb seals on loss characteristics in shroud cavities of an axial turbine 总被引:1,自引:0,他引:1
The loss in efficiency due to shroud leakage or tip clearance flow accounts for a substantial part of the overall losses in turbomachinery.It is important to identify the leakage loss characteristics in order to optimize turbomachinery.At present,little information is available in the open literature concerning the effect of honeycomb seals on the loss characteristics in shroud cavities of an axial turbine,despite of the widespread use of the honeycomb seals.Therefore,interaction between rotor labyrinth seal leakage flow with and without honeycomb facings and main flow is investigated to provide the loss characteristics of the mixing process of the re-entering leakage flow into the main flow.The effects of honeycomb seals on the flow in shroud cavities and interaction with the main flow are analyzed.An additional study on the impact of subtle shroud cavity exit geometry is also presented.The investigation results indicate that the honeycomb seal affects the over tip leakage flow and reduces mixing losses when compared to the solid labyrinth seal.The leakage flow interactions with the main flow have considerably changed the flow fields in the endwall regions.The proposed research reveals the effects of honeycomb seals on the loss characteristics in shroud cavities and the impact of subtle shroud cavity exit geometry,and it is helpful for the design optimization of turbomachinery. 相似文献