Unsteady flow of Carreau fluids around an impulsively moving circular cylinder is numerically investigated in this study. Both shear-thinning and shear-thickening fluids are used with the range of the power-index number 0.4 ≤ n ≤ 2. Unsteady laminar flow with the influence of shear-dependent viscosity and impulsive motions of the cylinder are analyzed with various Carreau numbers 10 ≤ Cu ≤ 40 and Reynolds numbers 10 ≤ Re ≤ 100. Both starting and stopping flows are numerically simulated. Systematic validation is conducted for current numerical approaches using literature data before the investigation of the unsteady flow. The effects of major Carreau fluid flow parameters, namely, n, Cu, and Re, on the unsteady vortical flow are studied with a focus on the formation of vortices, zero-shear point on the cylinder, and transitory hydrodynamic loads. In general, increased shear-thickening (n > 1 with higher Cu and lower Re) leads to higher viscous effect, delaying the formation of additional vortices and promoting the drag force due to the dominant viscous drag. More interesting flow aspects are noticed with shear-thinning fluids. Increased shear-thinning (n < 1 with higher Cu and higher Re) results in complicated vortical flow including secondary, tertiary, quaternary vortices, and even more. Highly oscillated drag force is obtained in such vortical flow due to the oscillated pressure drag, which dominates the total drag in the current unsteady flow. It is expected that the results reported in this study could be used for a better understanding of unsteady non-Newtonian fluid flow and for the validation of numerical simulation of unsteady non-Newtonian fluid flow.

中文翻译：

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Carreau流体在脉冲运动气缸周围的不稳定流动

在这项研究中，数值研究了Carreau流体在脉冲运动圆柱体周围的非稳态流动。两个剪切稀化和剪切稠化流体与电源索引号0.4的范围内使用≤ Ñ ≤2.剪切速率依赖粘度和气缸的脉冲运动的影响的非定常层流进行了分析与各种的Carreau号码10 ≤铜≤40和雷诺数10≤重新≤100都启动和停止流动进行了数值模拟。在研究非恒定流之前，使用文献数据对当前的数值方法进行系统验证。主要Carreau流体流量参数n，Cu和Re的影响，研究了非定常涡旋流动，重点是涡旋的形成，圆柱体上的零剪切点以及瞬态流体动力载荷。通常，增加剪切剪切厚度（n > 1，具有较高的Cu和较低的Re）会导致较高的粘性效应，从而延迟形成额外的涡流并由于占主导地位的粘性阻力而增强阻力。剪切稀化流体注意到了更有趣的流动方面。剪切稀化增加（n <1，具有较高的Cu和较高的Re）会导致复杂的涡流，包括次级，三级，四级涡流，甚至更多。由于振荡的压力阻力，在这种涡流中获得了高度振荡的阻力，该压力主导了当前非恒定流中的总阻力。可以预期，本研究报告的结果可用于更好地理解非稳态非牛顿流体流动，并用于验证非稳态非牛顿流体流动的数值模拟。