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基于存在自发凝结的湿蒸汽两相流动,开发了基于汽液两相双流体模型和k-ε-k_p湍流模型的计算方法,并对喷管和二维叶栅进行数值验证,结果表明本文所开发的方法具有较高的可靠性。对某汽轮机末级除湿静叶考虑除湿槽结构的二维流场进行了数值研究,指出在叶片表面开设除湿槽结构,能够显著影响涡轮叶栅内的非平衡凝结流动。由于除湿槽对水滴的抽吸作用使得叶栅内成核率峰值降低,且变化幅度减小,因此成核过程更为稳定。除湿槽结构使得叶栅内部大水滴数目减少,尾迹区水滴平均半径减小,叶栅出口湿度下降。 相似文献
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采用端壁边界层抽吸方法抑制时栅二次流的效果分析 总被引:1,自引:0,他引:1
1前言叶栅端壁边界层和叶片表面边界层的发展及其产生的各种旋涡和分离流动对二次流损失有着重要的影响[1,2],采用端壁边界层抽吸可以控制叶栅端壁上边界层的发展,从而降低二次流损失并改善出口气流的均匀性。同时,在汽轮机湿蒸汽静叶栅中有时也需在端壁上开设抽... 相似文献
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动叶围带顶部泄漏流动对透平级气动性能影响的数值研究 总被引:1,自引:0,他引:1
采用计算流体动力学软件CFX-TASCflow数值研究了带围带的动叶顶部间隙内泄漏流动对动叶流动效率以及下一级静叶进口气流角的影响特性.数值模拟了装有不同迷宫式汽封齿数时的动叶顶部间隙泄漏流动特性.揭示了泄漏流动不再是跨叶顶的横向流动,而是在叶顶间隙内沿着轴向流动.给出了动叶顶部间隙泄漏流场的结构,泄漏流与主流掺混后的流场对下游静叶性能的影响.研究结果表明泄漏流与动叶通道内的主流在动叶下游掺混后,改变了上半通道气流的流动方向,使这部分气流偏离设计工况,使下游静叶产生攻角损失.动叶顶部间隙泄漏流有较大的径向速度,在与主流掺混并进入动叶下游静叶后,会向着静叶中叶展处发展,改变静叶上半部流场的结构.动叶顶部间隙汽封齿数增多时这种效果就减小,静叶等熵效率的降低就越少,同时讨论了动叶顶部间隙泄漏流动对透平级气动性能的影响. 相似文献
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为了探究可调串列静子相对于常规可调静子的优势机理和流量调节极限,采用数值模拟方法分析了中低转速下某两级风扇在常规静子可调和串列静子可调两种情况下的变角度性能。结果表明:静子出口气流角决定下级转子部件流量,开大串列静子前叶可以提高静子部件流量,风扇整体流量由转静子部件流量共同限制;对中间级,调节常规静子会引起进出口几何角变化不匹配,改为串列可调后,在实现相同的出口几何角下,调节合适的串列前叶角度会大大减小静子损失,同时增大流通能力;对出口级,串列可调可以在保证风扇出口流动方向的前提下,调节串列前叶实现更高流通能力和更小损失;通过各级导叶静子匹配调节,与常规方案相比,串列方案的效率0.84以上的最大流量边界提高了10%。 相似文献
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单级高负荷向心透平三维黏性非定常计算 总被引:1,自引:0,他引:1
对一台单级高负荷向心透平进行了三维黏性定常和非定常计算,计算得到的动叶出口以及下游的周向平均流场与文献提供的实验结果符合良好。在此基础上对流动的非定常特性进行了分析,发现由于动叶转速较高,且动叶下游不存在下一级静叶的干涉,流动的非定常效应主要体现在叶片排之间的区域以及动叶通道进口,动叶出口以及下游流动的非定常特性并不明显。非定常计算结果透平的级效率随时间的波动幅度达到了1.3%。 相似文献
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空调风机叶道内旋涡流动分析及进气口偏心的影响 总被引:2,自引:0,他引:2
本文采用CFD方法,详细分析了空调用多翼离心风机叶道中的气流分布以及进气口偏心的影响。研究表明,风机叶道内存在大范围的气流分离现象。在后盘附近,存在分离现象的叶道约占2/3,主要分布在蜗壳内侧;而在“前盘”附近,几乎所有叶道都存在分离现象。在“前盘”附近,蜗舌下方的叶道中气流几乎停滞,蜗舌下游叶道为回流和尾缘旋涡所充满,至临近蜗壳出口侧,前缘旋涡逐步形成、发展并融合尾缘旋涡,最后衰减、消失。风机进气口向蜗壳内侧偏置适当距离, “前盘”附近叶道旋涡分布范围明显减小。 相似文献
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Experiments on the unsteady flow field and noise generation in a centrifugal pump impeller 总被引:4,自引:0,他引:4
Jong-Soo Choi Dennis K. McLaughlin Donald E. Thompson 《Journal of sound and vibration》2003,263(3):493-514
This paper reports on an experimental investigation of large-scale flowfield instabilities in a pump rotor and the process of noise generation by these instabilities. Measurements of the fluctuating components of velocity and surface pressure were made with hot-wire probes and surface mounted pressure transducers on a seven bladed back swept centrifugal water pump impeller operating with air as the working fluid. The impeller was operated without a volute or scroll diffuser, thereby eliminating any sound generation from pressure fluctuations on the volute cutoff. Thus the study focused on flow field and noise components other than the blade passage frequency (and its harmonics). The primary goal of the study was to provide fundamental information on the unsteady flow processes, particularly those associated with the noise generation in the device. It was further anticipated that detailed flow measurements would be useful for the validation of future computational simulations.The measured data at the discharge show a jet-wake type of flow pattern which results in a strong vorticity field. The flow with high velocity found on the pressure side of the impeller tends to move to the low-pressure region present at the suction side of the passage as a form of roll-up around the blade trailing edge. This motion causes an unsteady flow separation at the suction side of the blade and consequently disturbs the flow in the adjacent passage. By interacting with the impeller blades near the trailing edges, this instability flow causes a periodic pressure fluctuation on the blade surface and generates noise by a trailing edge generation mechanism. The spectrum of surface pressure measured at the trailing edge of each blade reveals a cluster of peaks which were identified with azimuthal mode numbers. The correlation between the acoustic farfield pressure and the surface pressure on the impeller blade has proven that the azimuthal modes synchronized with the number of impeller blades generate noise much more efficiently than the other modes. The paper also clarifies the correlation between unsteady flowfield measurements, in both impeller and laboratory co-ordinates, with the radiated noise properties. Thus some light is shed on the noise generation mechanisms of this particular device. 相似文献
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The results of the experimental study into the damping of flexural vibrations in turbofan blades with trailing edges tapered according to a power-law profile are reported. Trailing edges of power-law profile (wedges), with small pieces of attached absorbing layers, materialise one-dimensional acoustic black holes for flexural waves that can absorb a large proportion of the incident flexural wave energy. The experiments were carried out on four model blades made of aluminium. Two of them were twisted, so that a more realistic fan blade could be considered. All model blades, the ones with tapered trailing edges and the ones of traditional form, were excited by an electromagnetic shaker, and the corresponding frequency response functions have been measured. The results show that the resonant peaks are reduced substantially once a power-law tapering is introduced to the blade. An initial study into the aerodynamic implications of this method has been carried out as well, using measurements in a closed circuit wind tunnel. In particular, the effects of the trailing edge of power-law profile on the airflow-excited vibrations of the fan blades have been investigated. It has been demonstrated that trailing edges of power-law profile with appropriate damping layers are efficient in reduction of the airflow-excited vibrations of the fan blades. The obtained results demonstrate that power-law tapering of trailing edges of turbofan blades can be a viable method of reduction of blade vibrations. 相似文献
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R.E. Longhouse 《Journal of sound and vibration》1977,53(1):25-46
Noise and performance tests were conducted on three low tip speed, half-stage, axial flow fans to determine the nature of the vortex shedding noise mechanism. Each fan was 356 mm in diameter and had eight equally spaced, variable pitch blades. The noise measurements were made in a free field environment and the fan back pressure and speed were varied during the tests. An acenaphthene coating on the blades was used to determine the regions of laminar and turbulent flow.Vortex shedding can be a significant source of noise when the fan is operated in a lightly loaded condition. Essentially it is due to instabilities in the laminar boundary layer on the suction side of the blade where these instabilities are in the form of Tollmien-Schlichting (T-S) waves. These instabilities interact with the trailing edge of the blade and generate acoustic waves which radiate from the trailing edge and form a feedback loop with the source of the instabilities. Vortex shedding noise can contribute as much as 5 dB in overall noise level and up to 22 dB at higher frequencies (8–14 kHz).Serrations located at the leading edge, at the mid-chord, or near the trailing edge on the suction side were found to reduce the vortex shedding noise significantly. The mid-chord location was found to be the most satisfactory because, as well as eliminating the noise, the serrations provided a 3% improvement in peak efficiency. This improvement occurred because separation of the laminar boundary layer was prevented on the suction side. On the other hand, serrations placed at the other two locations tended to degrade fan performance. 相似文献
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本文在振荡来流条件下,数值模拟叶顶端翼对加装主动Gurney襟翼的垂直轴风力机叶片非定常气动特性的影响。采用NACA0015翼型的直叶片,并在尾缘前6%弦长位置安装主动襟翼。在最大出力工况(折合频率为0.1)下,对比原型叶片,加装主动襟翼叶片的切向力系数提高了4.47%,安装有叶顶端翼的主动襟翼叶片的切向力系数提高21.18%。通过比较叶片端部涡结构分布,发现叶顶端翼不仅阻止了叶片压力面及吸力面的叶梢涡分支在尾缘处汇合,同时也隔断了主动襟翼产生的角涡与叶梢涡的融合,有效的降低了叶片端部损失,提升了风力机的整体性能。 相似文献