复杂形状进气箱与叶轮一体的斜流风机内部湍流数值分析

本文采用混合平面法实施通流元件之间的流场信息传递，旨在建立斜流风机统一正命题的流动模型与数值方法。将非正交曲线坐标系下压力修正法求解K-ε模型封闭Reynolds时均方程的三维程序模块化，使其可适用于静止及旋转坐标系，过气箱与叶轮采用各自独立的贴体网格，按照串行方法轮换调用计算模块并在进气箱出口与叶轮进口之间设置混合平面，用以传递与转换动静元件之间耦合流动的信息，在单一微机系统上实现了从进气箱进口到叶轮出口的整机内部湍流的一体计算。采用上述方法数值模拟了某斜流风机的内部流场，计算与已有实验结论大体吻合．     

Relationship between volute pressure fluctuation pattern and tonal noise generation in a squirrel-cage fan

In this work, the pressure fluctuation pattern in the volute of a squirrel-cage fan is analyzed. Also studied is how this pattern is modified when a slight geometry change is introduced in the volute tongue. The study has been carried out on a commercial machine, used in automotive air conditioning units. A three-dimensional and unsteady numerical simulation of the flow in the complete machine has been carried out using the commercial code FLUENT. In this way, the pressure fluctuations in some locations near the volute wall have been obtained. The results of this numerical simulation have been compared to the sound pressure level spectra radiated by the fan, measured in a ducted test installation at the laboratory. The tendencies of the sound pressure levels measured at the blade passing frequency show a good correlation with the amplitudes of pressure fluctuations obtained numerically near the volute wall.     

On the theorem on asymptotic equidistribution of the convolution powers of symmetric measures on a unimodular group

The theorem on the asymptotic equidistribution of the convolution powers of a symmetric probability measure given on a unimodular group [1] deals with a measure whose convolution powers, starting from one of them, load an arbitrary prescribed nonempty subset of the group. In the present note, we indicate the modifications that arise under the replacement of the above condition by the requirement that the smallest closed subgroup (of the group considered) generated by the support of this measure coincide with the group itself. Translated fromMatematicheskie Zametki, Vol. 60, No. 1, pp. 120–126, July, 1996. This research was partially supported by the International Science Foundation under grant No. 3J000.     

Decompositions of Graphs into Fans and Single Edges

Given two graphs G and H , an H‐decomposition of G is a partition of the edge set of G such that each part is either a single edge or forms a graph isomorphic to H . Let be the smallest number ? such that any graph G of order n admits an H‐decomposition with at most ? parts. Pikhurko and Sousa conjectured that for and all sufficiently large n , where denotes the maximum number of edges in a graph on n vertices not containing H as a subgraph. Their conjecture has been verified by Özkahya and Person for all edge‐critical graphs H . In this article, the conjecture is verified for the k‐fan graph. The k‐fan graph , denoted by , is the graph on vertices consisting of k triangles that intersect in exactly one common vertex called the center of the k‐fan.     

核电站一回路用机械密封

机械密封在各类核电站的一回路中有大量应用.核电站一回路用机械密封是核电站的关键部件之一,其性能好坏很大程度上决定着核电站能否长周期安全可靠运行.本文以几种具有代表性的核电站反应堆堆型为例,对其一回路用机械密封进行了介绍,这些反应堆分别以水、氦气和液态金属为冷却剂并跨越第二代到第四代核电技术.首先介绍了压水堆核主泵机械密封,分别叙述了美式风格的流体静压型核主泵密封及欧式风格的流体动压型核主泵密封的结构特点、工作原理和最新的基础研究状况;随后介绍了高温气冷堆氦气轮机/氦气风机干气密封的结构特点、使用要求及相应的针对性设计;最后介绍了钠冷快堆钠泵机械密封,包括1种惰性气体缓冲、油膜润滑的三级串联式机械密封和1种直接以液态金属润滑的螺旋槽式机械密封.     

Aerodynamic damping of sidewall bounded oscillating cantilevers

As a result of their simplicity, low power consumption, and relative ease of implementation, oscillating cantilevers have been investigated for use in multiple applications. However, the in situ operation in many cases, requires oscillating near one or more solid walls. When the separation distance between the vibrating cantilever and the solid wall becomes small, damping from the surrounding fluid is increased, which in turn can increase the power required to maintain certain operational performance characteristics (e.g., vibration amplitude). This increase in damping is a well-studied phenomenon for certain configurations (e.g., microcantilevers in Atomic Force Microscopy, or AFM), but is largely unexplored for a cantilever sweeping across a solid wall, which has direct impact for many macro-based applications including electronics cooling and propulsion. In this paper, we experimentally investigate the aerodynamic damping as a function of the gap between two sidewalls parallel to the oscillating motion of the cantilever. Multiple voltage and frequency inputs are considered in addition to the magnitude of the wall to cantilever gap. Experiments performed across a range of operating conditions reveal that decreasing the distance between the walls and the oscillating cantilever can increase the aerodynamic damping as much as 5 times that of the isolated (i.e., without sidewalls) operation. The resonance frequency is also shown to decrease when the gap spacing is extremely small, suggesting the added mass of the fluid is also sensitive to this variable. However, this change is much smaller (~0.5%) compared to the change typically observed in damping. The findings in the paper help to quantify the overall effect of solid enclosure walls on the performance of an oscillating cantilever, which will better enable the designer to achieve the maximum operational effectiveness. The experimental findings also suggest viscous damping with sidewalls could be predicted from first principles in a similar manner to well accepted analytical models of a cantilever vibrating above a solid surface.     

前置导叶对横流风机性能及气动噪声的影响

在横流风机叶轮前加前置导叶(IGV)可以改善横流风机的进口流场,减少叶片上的流动分离,进而降低横流风机的功率。采用非结构化网格RNGκ-ε两方程模型,分别对不加IGV、加IGV1,以及IGV2的横流风机内部流场进行数值模拟,并对三种情况进行气动性能及噪声试验。数值模拟和试验结果表明在加不同IGV以后,横流风机的噪声增大,但是功率在加IGV2后出现了一定的降低。