由两个风扇转子设计得到的启示

本文对两个风扇转子设计进行了总结,从设计过程突破问题的关键以及流动的组织方面看,得到了几点有益启示,值得在新型叶轮机设计及有关问题研究中引以借鉴。     

Polyhedra with the Integer Carathéodory Property

A polyhedron P has the Integer Carathéodory Property if the following holds. For any positive integer k and any integer vector w∈kP, there exist affinely independent integer vectors x₁,…,xt∈P and positive integers n₁,…,nt such that n₁+?+nt=k and w=n₁x₁+?+ntxt.In this paper we prove that if P is a (poly)matroid base polytope or if P is defined by a totally unimodular matrix, then P and projections of P have the Integer Carathéodory Property. For the matroid base polytope this answers a question by Cunningham from 1984.     

离心风机子午通道内湍流场数值模拟

由进风口－叶轮－无叶扩压器－蜗壳等部件组成的离心风机通道内流分析是非常复杂的，目前还只能是分别计算各部件内的流场，但必须考虑部件间的相互影响。本文采用轴对称Ｎ－Ｓ方程，根据三维叶轮通道计算给出的叶片力分布，求解了考虑叶片力的进风口－叶轮－无叶扩压器组成的子午通道问题，所得结果可用来给出三维叶轮通道计算的进口条件，并可用于优化设计进风口及叶轮前、后盘形状。该方法已得到实践检验。     

某轴流送风机叶片断裂事故计算分析

本文是理论计算与工程实际相结合的典型例子．某电厂锅炉送风机，多次发生叶片断裂事故，严重影响了电厂生产的正常运行，受电厂委托，我所就风机动叶片断裂事故，采用有限元方法对转子、支承结构、壳体和动叶片均进行了一系列的计算分析，找出了故障原因，并提出了改进措施．     

A sufficient condition for planar graphs with maximum degree 8 to be 9-totally colorable

A total k-coloring of a graph G is a coloring of V(G) ∪ E(G) using k colors such that no two adjacent or incident elements receive the same color. The total chromatic number χ'(G) is the smallest integer k such that G has a total k-coloring. It is known that if a planar graph G has maximum degree Δ≥ 9, then χ'(G) = Δ + 1. In this paper, we prove that if G is a planar graph with maximum degree 8 and without a fan of four adjacent 3-cycles, then χ'(G) = 9.     

多联机双风轮系统拍振分析与性能优化研究

各品牌的中央空调多联室外机均采用双风轮系统,都存在不同程度的低频脉动异音,异音呈低频特性,易让人产生烦躁感.双风轮系统在旋转基频比较接近的情况下运转时,旋转噪声叠加后产生拍振异音,其频率等于双风轮的旋转基频差.旋转噪声是拍振腹能量的主要来源.本文设计了新三叶风轮,采用新三叶风轮与原四叶风轮组合方式运行.同时测试两风轮的...     

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.