Doostmohammadi A, Ardekani A M
Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA.
Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA and School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Sep;90(3):033013. doi: 10.1103/PhysRevE.90.033013. Epub 2014 Sep 22.
Density interfaces in the water column are ubiquitously found in oceans and lakes. Interaction of settling particles with pycnoclines plays a pivotal function in nutrient transport between ocean layers and settling rates of marine particles. We perform direct numerical simulations of an elongated particle settling through a density interface and scrutinize the role of stratification on the settling dynamics. It is found that the presence of the density interface tends to turn the long axis of an elongated particle parallel to the settling direction, which is dramatically different from its counterpart in a homogeneous fluid. Although broadside-on settling of the elongated particle is enhanced upon approaching the interface, the long axis rotates toward the settling direction as the particle passes through the interface. We quantify turning couples due to stratification effects, which counteract the pressure-induced torques due to the fluid inertia. A similar behavior is observed for different initial orientations of the particle. It is shown that the reorientation of an elongated particle occurs in both sharp and linear density stratifications.
水柱中的密度界面在海洋和湖泊中普遍存在。沉降颗粒与温跃层的相互作用在海洋层间的营养物质传输和海洋颗粒的沉降速率中起着关键作用。我们对细长颗粒通过密度界面的沉降进行了直接数值模拟，并仔细研究了分层对沉降动力学的作用。研究发现，密度界面的存在倾向于使细长颗粒的长轴平行于沉降方向，这与它在均匀流体中的情况有很大不同。尽管细长颗粒在接近界面时侧向沉降会增强，但当颗粒穿过界面时，长轴会转向沉降方向。我们量化了由于分层效应产生的转向力矩，这些力矩抵消了由流体惯性引起的压力诱导力矩。对于颗粒的不同初始取向，也观察到了类似的行为。结果表明，细长颗粒的重新定向在急剧和线性密度分层中都会发生。
