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采用具有QUICK差分格式的SIMPLE算法对底部加热长方体腔内空气的自然对流进行了实验研究和数值计算.1)当四周壁面绝热时,腔内流体形成平行于短轴方向的多个长条状涡卷,而平行于长轴方向没有形成涡卷.当Rayleigh数较小时,腔内流动表现出明显的二维特性,沿短轴各个截面的涡卷流动基本一致,三维模型平行于短轴的各截面平均Nusselt数除了边壁处差别较大,中间大部分区域均与二维模型平均Nusselt数比较接近,腔内的空气流动在长轴方向除了边壁附近差别较大,中间大部分区域均呈现明显的二维特性,二维与三维模型计算结果一致,且与实验结果吻合.随着Rayleigh数的增加,涡卷数量与形状都会发生改变,在腔内出现多边形的涡卷,腔内的流动表现出明显的三维特性,此时采用三维模型才能取得与实验一致的计算结果.2)侧壁绝热或者传热量较小时,长高比为16时,三维模型计算得到与实验一致的结果,形成平行于短轴的10个长条状涡卷.当侧壁面有传热时,方腔内流动形成了平行于长轴方向的涡卷,并且热流方向相反时涡卷的旋转方向也相反.3)底部加热长方体腔内空气的自然对流换热,低Rayleigh数时流动和换热处于稳态,当Rayleigh数超过某一临界值时,流动和换热就会发生非线性振荡.随着Rayleigh数的增加,流动的情况基本分成四个区域:稳定区域、单倍周期区域、多倍周期区域和混沌区域.
The SIMPLE algorithm with QUICK difference scheme was used to study the natural convection of the air in the bottom heating cuboid chamber. 1) When the surrounding walls were adiabatic, the fluid in the cavity formed a plurality of long vortexes parallel to the short axis While no scroll is formed parallel to the long axis.When the Rayleigh number is small, the intracavity flow shows obvious two-dimensional characteristics, and the eddy flows in each section along the short axis are basically the same. The three-dimensional model is parallel to each of the short axis In addition, the average Nusselt number of cross section is quite different from that at the side wall, most of the middle region are close to the average Nusselt number of the two-dimensional model, and the air flow in the cavity is greatly different except the vicinity of the side wall in the long axis, Obvious two-dimensional characteristics, two-dimensional and three-dimensional model of the calculated results, and consistent with the experimental results.With the increase of Rayleigh number, the volume and shape of the scroll will change, appear in the cavity polygon scroll, cavity flow Showing obvious three-dimensional characteristics, the use of three-dimensional model can get consistent with the experimental results.2) When the wall insulation or heat transfer is small, the height-to-height ratio of 16, the three-dimensional model Calculated and consistent with the experimental results, the formation of 10 parallel to the short axis of the scrolls.When the side wall surface heat transfer, the formation of a square cavity flow parallel to the direction of the long axis of the scroll, and the heat flow in the opposite direction The direction of rotation of the scroll is reversed.3) The natural convective heat transfer of the air inside the rectangular box body heated at the bottom, the steady state at low Rayleigh number, and the flow and heat transfer when the Rayleigh number exceeds a certain critical value Nonlinear oscillations occur.With the increase of Rayleigh number, the flow is basically divided into four regions: stable region, single cycle region, multiple cycle region and chaotic region.