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采用非稳态的层流模型对竖直通道内竖直布置的两根水平圆管的自然对流换热进行了数值模拟研究.分析了管间距对圆管自然对流流动和换热以及时间特性的影响.数值模拟结果表明:随着管间距S的增大,上下管之间的流动增强,上管换热的增强幅度较下管明显,Ra越大,上管的换热增强越明显.在Ra=108时,上下管的换热并不随着S的变化而呈现单调的变化.不同参数下,上下管的换热呈现出稳态、准周期振荡、周期振荡和混沌的时间特性.所得结果可为管束式换热器的传热计算提供理论参考.“,”Numerical simulation is performed by adopting unsteady laminar mode for the natural convection around a pair of horizontal cylinders confined in a vertical channel.The influence of the longitudinal pitch between the cylinders on the flow and heat transfer and their transient characterization is analyzed.The numerical results show that,the flow between the two horizontal cylinders become intensive with increase of the longitudinal pitch S,and the effect of the heat transfer enhancement on the upper cylinder is more obvious than that on the lower one,the extent of the upper cylinder's heat transfer enhancement is larger than that of the lower one's with increase of Rayleigh number.When Ra=108,the heat transfer of the two cylinders is not monotonic function of S.The transient characterization of the heat transfer of the cylinders are summarized.And with changes of Rayleigh number and the longitudinal pitch,the transient characteristic of the heat transfer of two horizontal cylinders appear steady-state,quasi-periodic oscillatory,periodic oscillatory and chaotic.The results can be theoretical reference for the calculation of heat transfer in tube bundle heat exchanger.