The dynamical motion of a pair of microparticles exposed to acoustic standing waves and located at the pressure nodal plane is studied using numerical simulations and experiments. The insight into their dynamical behavior along the pressure nodal plane due to the competition between the axial primary radiation and interparticle forces is elucidated. An expression for axial primary radiation force acting on a particle is derived, and the particle dynamics is simulated using fluid-structure interaction model based on the arbitrary Lagrangian-Eulerian method. Considering the total radiation force acting on a particle is the sum of the axial primary radiation force and the interparticle force, three distinct dynamical regimes are observed depending upon the relative magnitudes of the acoustic forces which in turn depend on the gradient of the acoustic energy density. Acceleration, deceleration, and constant velocity motion of the pair of approaching particles are observed, which are explained by the interplay of the acoustic and non-acoustic forces. The dynamical motion of the pair of particles predicted using the model is in very good agreement with the experimental observations.

中文翻译：

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轴向初级辐射和粒子间力共同作用下一对微粒在声压节点平面的动力学运动

使用数值模拟和实验研究了一对暴露于声驻波并位于压力节点平面的微粒的动力学运动。阐明了由于轴向初级辐射和粒子间力之间的竞争而沿压力节点平面的动力学行为。推导出作用在粒子上的轴向初级辐射力的表达式，并使用基于任意拉格朗日-欧拉方法的流固耦合模型来模拟粒子动力学。考虑到作用在粒子上的总辐射力是轴向初级辐射力和粒子间力之和，观察到三种不同的动力学状态，这取决于声力的相对大小，而声力又取决于声能密度的梯度。观察到这对接近的粒子的加速、减速和匀速运动，这是通过声学和非声学力的相互作用来解释的。使用该模型预测的这对粒子的动力学运动与实验观察非常吻合。