In this study, the dynamic response of a neutrally buoyant elliptical cylinder is investigated for a two-dimensional shear flow over a wide range of aspect ratios ( where, and are the major and minor axis radii, respectively). Parametric studies were carried out for confinement ratios () that vary the distance between the particle and the domain walls (H) for shear-rate (G) based Reynolds number The simulations were performed using the signed distance field-immersed boundary method (SDFIBM) algorithm implemented in OpenFOAM. The motion of the particle is limited to free rotation about the axis through the centroid without any translational freedom. This work demonstrates and affirms two distinct responses of the elliptical particle in shear flow: (1) a periodical rotating stage that exhibits a relaxation type of response and (2) a spontaneously locked stationary stage, where the net torque becomes zero. A critical Reynolds number () demarcates the transition between these two stages, and it depends on aspect ratio and confinement ratio. The prediction of was found to be in excellent agreement with the experimentally reported data in the literature, validating the SDFIBM for particles subjected to shear flows.

中文翻译：

---

对剪切流中自由旋转椭圆粒子动力学的进一步贡献

在这项研究中，研究了中性浮力椭圆圆柱体在宽纵横比范围内的二维剪切流的动态响应（其中和分别是长轴半径和短轴半径）。对基于雷诺数的剪切速率 ( G ) 改变粒子与畴壁 ( H )之间距离的限制比 () 进行了参数研究。使用符号距离场浸没边界法 (SDFIBM) 进行了模拟在 OpenFOAM 中实现的算法。粒子的运动仅限于绕轴通过质心，没有任何平移自由度。这项工作证明并肯定了椭圆粒子在剪切流中的两种不同响应：（1）表现出松弛型响应的周期性旋转阶段和（2）自发锁定的静止阶段，其中净扭矩变为零。临界雷诺数 ( ) 界定了这两个阶段之间的过渡，它取决于纵横比和限制比。发现的预测与文献中实验报告的数据非常一致，验证了 SDFIBM 对于受到剪切流的颗粒。