论文标题
低雷诺数的非牛顿动荡的喷气机
Non-Newtonian turbulent jets at low-Reynolds number
论文作者
论文摘要
我们在低雷诺数下的非牛顿流体的平面喷气器进行直接数值模拟，在纽顿液体的典型层流条件下。我们选择了三种以剪切粉状（Carreau），粘弹性（Oldroyd-B）和剪切和粘弹性（Giesekus）为特征的非牛顿流体模型（Giesekus），并对产生的流量统计进行彻底分析。我们观察到，随着魏森伯格数量的增加，射流从低魏森堡数量的层流转变为高魏森伯格数量的湍流。我们表明，不同的非牛顿特征及其组合产生了相当不同的流动制度，源自粘性，弹性和惯性效应的竞争。我们观察到粘弹性和剪切粉都可以发展不稳定，并导致随之而来的过渡到湍流的流动状态。但是，纯粘弹性的Oldroyd-B流体在魏森贝格的数量低于纯薄薄的碳酸液体的发作，其魏森堡的发作发作。当两个效果都存在时，发现了一个中间条件，这表明在这种情况下，剪切特征是对流体弹性的作用。尽管在流动状态下观察到的质量差异，但批量统计数据，即中心线速度和喷射厚度，遵循几乎相同的层层和动荡的牛顿平面喷气机获得的幂律量表。
We perform direct numerical simulations of planar jets of non-Newtonian fluids at low Reynolds number, in typical laminar conditions for a Newtonian fluid. We select three different non-Newtonian fluid models characterized by shear-thinning (Carreau), viscoelasticity (Oldroyd-B) and shear-thinning and viscoelasticity together (Giesekus), and perform a thorough analysis of the resulting flow statistics. We observe that, as the Weissenberg number is increased, the jet transitions from a laminar flow at low Weissenberg number, to a turbulent flow at high Weissenberg number. We show that the different non-Newtonian features and their combination give rise to rather different flowing regimes, originating from the competition of viscous, elastic and inertial effects. We observe that both viscoelasticity and shear-thinning can develop the instability and the consequent transition to a turbulent flowing regime; however, the purely viscoelastic Oldroyd-B fluid exhibits the onset of disordered fluid motions at a lower Weissenberg number than what observed for the purely shear-thinning Carreau fluid. When the two effects are both present, an intermediate condition is found, suggesting that, in this case, the shear-thinning feature is acting against the fluid elasticity. Despite the qualitative differences observed in the flowing regime, the bulk statistics, namely the centerline velocity and jet thickness, follow almost the same power-law scalings obtained for laminar and turbulent Newtonian planar jets.
