We report a unique tuneable analogue trend in particle focusing in the laminar and weak viscoelastic regime of elasto-inertial flows. We observe experimentally that particles in circular cross-section microchannels can be tuned to any focusing bandwidths that lie between the “Segre-Silberberg annulus” and the centre of a circular microcapillary. We use direct numerical simulations to investigate this phenomenon and to understand how minute amounts of elasticity affect the focussing of particles at increasing flow rates. An Immersed Boundary Method is used to account for the presence of the particles and a FENE-P model is used to simulate the presence of polymers in a Non-Newtonian fluid. The numerical simulations study the dynamics and stability of finite size particles and are further used to analyse the particle behaviour at Reynolds numbers higher than what is allowed by the experimental setup. In particular, we are able to report the entire migration trajectories of the particles as they reach their final focussing positions and extend our predictions to other geometries such as the square cross section. We believe complex effects originate due to a combination of inertia and elasticity in the weakly viscoelastic regime, where neither inertia nor elasticity are able to mask each other’s effect completely, leading to a number of intermediate focusing positions. The present study provides a fundamental new understanding of particle focusing in weakly elastic and strongly inertial flows, whose findings can be exploited for potentially multiple microfluidics-based biological sorting applications.

我们报告了粒子惯性在层流和弱惯性流的弱粘弹性状态下的独特可调谐模拟趋势。我们通过实验观察到，可以将圆形横截面微通道中的粒子调整为位于“ Segre-Silberberg环空”和圆形微毛细管中心之间的任何聚焦带宽。我们使用直接数值模拟来研究这种现象，并了解微小的弹性如何在增加的流速下影响颗粒的聚焦。沉浸边界方法用于说明粒子的存在，而FENE-P模型用于模拟非牛顿流体中聚合物的存在。数值模拟研究了有限尺寸颗粒的动力学和稳定性，并进一步用于分析雷诺数高于实验设置所允许值的颗粒行为。特别是，我们能够报告粒子到达其最终聚焦位置时的整个迁移轨迹，并将我们的预测扩展到其他几何形状，例如正方形横截面。我们认为，复杂的效果是由弱粘弹性状态下的惯性和弹性共同产生的，惯性和弹性都无法完全掩盖彼此的效果，从而导致出现许多中间聚焦位置。本研究为弱弹性和强惯性流中的粒子聚焦提供了基础的新认识，