Boffetta G, Mazzino A, Musacchio S
Dipartimento di Fisica Generale and INFN, Università di Torino, via P.Giuria 1, I-10125 Torino, Italy.
Phys Rev E Stat Nonlin Soft Matter Phys. 2011 May;83(5 Pt 2):056318. doi: 10.1103/PhysRevE.83.056318. Epub 2011 May 16.
The role of polymer additives on the turbulent convective flow of a Rayleigh-Taylor system is investigated by means of direct numerical simulations of Oldroyd-B viscoelastic model. The dynamics of polymer elongations follows adiabatically the self-similar evolution of the turbulent mixing layer and shows the appearance of a strong feedback on the flow which originates a cutoff for polymer elongations. The viscoelastic effects on the mixing properties of the flow are twofold. Mixing is appreciably enhanced at large scales (the mixing layer growth rate is larger than that of the purely Newtonian case) and depleted at small scales (thermal plumes are more coherent with respect to the Newtonian case). The observed speed up of the thermal plumes, together with an increase of the correlations between temperature field and vertical velocity, contributes to a significant enhancement of heat transport. Our findings are consistent with a scenario of drag reduction induced by polymers. A weakly nonlinear model proposed by Fermi for the growth of the mixing layer is reported in the Appendix.
通过对奥尔德罗伊德 - B粘弹性模型进行直接数值模拟，研究了聚合物添加剂对瑞利 - 泰勒系统湍流对流流动的作用。聚合物伸长的动力学绝热地跟随湍流混合层的自相似演化，并显示出对流动有强烈反馈的现象，这种反馈导致了聚合物伸长的截断。粘弹性对流动混合特性的影响是双重的。在大尺度上混合明显增强（混合层生长速率大于纯牛顿流体情况），而在小尺度上混合减少（相对于牛顿流体情况，热羽流更连贯）。观察到的热羽流加速，以及温度场和垂直速度之间相关性的增加，有助于显著增强热传输。我们的发现与聚合物引起的减阻情况一致。附录中报告了费米提出的关于混合层生长的弱非线性模型。
