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Two-layer channel flow involving a fluid with time-dependent viscosity
Environmental Fluid Mechanics ( IF 2.2 ) Pub Date : 2021-06-24 , DOI: 10.1007/s10652-021-09803-8
Kirti Chandra Sahu

A pressure-driven two-layer channel flow of a Newtonian fluid with constant viscosity (top layer) and a fluid with a time-dependent viscosity (bottom layer) is numerically investigated. The bottom layer goes through an ageing process in which its viscosity increases due to the formation of internal structure, which is represented by a Coussot-type relationship. The resultant flow dynamics is the consequence of the competition between structuration and de-structuration, as characterised by the dimensionless timescale for structuration \((\tau )\) and the dimensionless material property \((\beta )\) of the bottom fluid. The development of Kelvin-Helmholtz type instabilities (roll-up structures) observed in the Newtonian constant viscosity case was found to be suppressed as the viscosity of the bottom layer increased over time. It is found that, for the set of parameters considered in the present study, the bottom layer almost behaves like a Newtonian fluid with constant viscosity for \(\tau >10\) and \(\beta >1\). It is also shown that decreasing the value of the Froude number stabilises the interfacial instabilities. The wavelength of the interfacial wave increases as the capillary number increases.



中文翻译:

两层通道流动,涉及具有随时间变化的粘度的流体

数值研究了具有恒定粘度的牛顿流体(顶层)和具有随时间变化的粘度的流体(底层)的压力驱动的两层通道流动。底层经过老化过程,由于内部结构的形成,其粘度增加,以Coussot型关系表示。由此产生的流动动力学是结构化和解构化之间竞争的结果,其特征在于结构化的无量纲时间尺度\((\tau )\)和无量纲的材料属性\((\beta )\)底部流体。发现在牛顿恒定粘度情况下观察到的开尔文-亥姆霍兹型不稳定性(卷起结构)的发展被发现随着底层的粘度随时间增加而受到抑制。发现,对于本研究中考虑的一组参数,底层几乎表现得像牛顿流体,对于\(\tau >10\)\(\beta >1\)具有恒定的粘度。还表明,降低弗劳德数的值可以稳定界面不稳定性。界面波的波长随着毛细管数的增加而增加。

更新日期:2021-06-25
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