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采用激光全息干涉照相技术和烟可视化方法,对底部加热长方体腔内空气自然对流的流动和换热的流场、温度场、三维特性及自维持振荡现象进行实验研究.通过仪表校核与误差分析,验证了恒温壁面均温性、激光干涉测量精度,并且得出如下实验结果:1)随着Ra数的增加,流动开始表现得不稳定,等温线也发生扭曲.当Ra数达到12500时,出现涡卷消融的现象,当Ra数超到18500时,不仅沿短轴方向出现涡卷,而且沿长轴方向也开始出现涡卷,上升的气流向四周降落,呈现羽毛状,流动由二维特性开始向三维特性转变.2)通过实验观察发现,在Ra数比较小的情况下,流动经过一系列变化过程之后,最后稳定在某一状态;随着Ra数的增加,流动变得越来越快,越来越趋于不稳定,当超过某一临界值Rac=30500时,流动表现的不稳定,流场随时间不断变化,开始进入到非线性状态.3)当侧壁面向外漏热时,腔内流体会形成平行于长轴方向的两个长条状涡卷,涡卷从中间位置上升,从壁面两侧下降,并且实验过程中会出现三个涡卷的消融状态.
The laser holographic interferometry photography and smoke visualization method were used to study the flow field, temperature field, three-dimensional characteristics and self-sustaining oscillation of the natural convection flow and heat transfer in the heated rectangular cubical cavity bottom. The instrument calibration and error analysis The experimental results show that: 1) As the Ra number increases, the flow begins to appear unstable and the isotherm also distorts.When the number of Ra reaches 12500, When the Ra number exceeds 18500, not only the scrolls appear along the short axis, but also the scrolls begin to appear along the long axis. The ascending airflow descends all around and feathers appear, and the flow from the two-dimensional The characteristic begins to change to the three-dimensional characteristic.2) The experimental observation shows that when the Ra ratio is small, the flow finally stabilizes in a certain state after a series of changing processes, and as the Ra number increases, the flow becomes more and more The faster, more and more tended to instability, when a certain threshold Rac = 30500, the performance of the flow instability, the flow field changes over time, began to enter the non-linear state .3) When hot, The fluid will be formed parallel to the longitudinal direction of the two elongated wrap, wrap rises from the intermediate position, the wall decreases from both sides, and during the experiment were melting occurs three scrolls.