非牛顿流体在介质中的自然对流与传热

THERMAL CONVECTION OF A VISCOELASTIC FLUID IN A POROUS LAYER HEATED FROM BELOW

基于修正的Darcy定律,数值模拟了上端开口,从底部等温加热的多孔介质中黏弹性流体的自然对流与传热,其中使用了特征松弛时间λ和迟滞时间ε来表征黏弹性流体的性质。我们选择了三组不同的λ和ε.发现与牛顿流体中对应的情况相比,黏弹性流体的传热特性有很大不同。另外,上端开口多孔介质中的黏弹性流体比上端闭口多孔介质中黏弹性流体的自然对流与传热也有很大不同.在不同的Ra数范围,传热规律服从不同的标度律。

By using the modified Darcy＇s law and a second-order central differential method,a direct numerical simulation is done with thermal convection of viscoelastic fluid in an open-top porous medium heated from below.Two characteristic time constantsλandεare used to describe the viscoelastic properties,and three different series of them are chosen.The heat transport characteristic of viscoelastic fluid is quite different from that of Newtonian fluid.Some comparisons with the results of viscoelastic fluid in a closed-top porous square box heated from below show：heat transport of open-top case is more efficient than that of closed-top case.Some scaling laws are found at Rayleigh numbers as low as 100.