The periodic unsteady natural convection flow and heat transfer in a square enclosure containing a heated circular cylinder with different vertical locations is numerically studied. The temperature of the enclosure keeps lower constant while the temperature of the inner circular cylinder oscillates periodically with time at higher averaged value, the natural convection in the enclosure is driven by the temperature difference. The two-dimensional natural convection is simulated with high accuracy temporal spectral method and local radial basis functions method at Rayleigh number Ra = 10⁵. The location of inner circular cylinder varies from −0.25 to 0.25 vertically, the temperature pulsating amplitudes are a = 0.5, 1.0 and 1.5 and the temperature pulsating period ranges from 0.01 to 100. Numerical results show that the heat transfer is strongly dependent on the vertical location and the pulsating temperature of inner cylinder. The heat transfer is enhanced generally for the time-periodic unsteady natural convection comparing with its steady state natural convection, and the local maximum heat transfer rate is observed for some locations. Moreover, the phenomenon of backward heat transfer is discussed and the quantity of back heat transfer rate is presented. Finally, the influence of the vertical locations and pulsating temperature on the unsteady fluid flow and heat transfer are discussed and analyzed.

数值研究了一个方形外壳中的周期性非稳态自然对流流动和热传递，该方形外壳包含一个具有不同垂直位置的加热的圆柱体。外壳的温度保持较低的恒定值，而内部圆柱体的温度则以较高的平均值随时间周期性地振荡，外壳中的自然对流由温度差驱动。二维自然对流通过瑞利数Ra  = 10 ^5的高精度时域光谱法和局部径向基函数法进行模拟。内圆筒的位置从-0.25到0.25变化垂直，温度脉动振幅一 = 0.5、1.0和1.5，温度脉动周期的范围从0.01到100。数值结果表明，传热很大程度上取决于垂直位置和内筒的脉动温度。与稳态自然对流相比，时间周期非稳态自然对流的传热通常得到增强，并且在某些位置观察到局部最大传热速率。此外，讨论了反向传热现象，并提出了反向传热速率的数量。最后，讨论并分析了垂直位置和脉动温度对非稳态流体流动和传热的影响。