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Abstract：
Gliding is a crucial phase in swimming, yet the understanding of fluid force and flow fields during gliding remains incomplete. This study analyzes gliding through Computational Fluid Dynamics simulations. Specifically, a numerical model based on the Smoothed Particle Hydrodynamics (SPH) method for flow-object interactions is established. Fluid motion is governed by continuity, Navier-Stokes, state, and displacement equations. Modified dynamic boundary particles are used to implement solid boundaries, and steady and uniform flows are generated with inflow and outflow conditions. The reliability of the SPH model is validated by replicating a documented laboratory experiment on a circular cylinder advancing steadily beneath a free surface. Reasonable agreement is observed between the numerical and experimental drag force and lift force. After the validation, the SPH model is employed to analyze the passive drag, vertical force, and pitching moment acting on a streamlined gliding 2D swimmer model as well as the surrounding velocity and vorticity fields, spanning gliding velocities from 1 m/s to 2.5 m/s, submergence depths from 0.2 m to 1 m, and attack angles from -10° to 10°. The results indicate that with the increasing gliding velocity, passive drag and pitching moment increase whereas vertical force decreases. The wake flow and free surface demonstrate signs of instability. Conversely, as the submergence depth increases, there is a decrease in passive drag and pitching moment, accompanied by an increase in vertical force. The undulation of the free surface and its interference in flow fields diminish. With the increase in the attack angle, passive drag and vertical force decrease whereas pitching moment increases, along with the alteration in wake direction and the increasing complexity of the free surface. These outcomes offer valuable insights into gliding dynamics, furnishing swimmers with a scientific basis for selecting appropriate submergence depth and attack angle.
摘要：
滑翔是游泳的关键阶段,然而，对滑翔过程中流体力和流场的理解仍然不完整。本研究通过计算流体动力学模拟分析滑翔。具体来说,建立了基于平滑粒子流体动力学（SPH）方法的流-物相互作用的数值模型。流体运动是由连续性控制的，Navier-Stokes,state,和位移方程。修改后的动态边界粒子用于实现实体边界，在流入和流出条件下产生稳定均匀的流动。通过在自由表面下方稳定前进的圆柱体上复制有记录的实验室实验，验证了SPH模型的可靠性。在数值和实验阻力和升力之间观察到合理的一致性。验证后，SPH模型用于分析被动阻力，垂直力,以及作用在流线型滑翔2D游泳模型上的俯仰力矩，以及周围的速度场和涡度场，滑翔速度从1米/秒到2.5米/秒，淹没深度从0.2米到1米，攻角从-10°到10°。结果表明,随着滑翔速度的增加,被动阻力和俯仰力矩增加，而垂直力减小。尾流和自由表面显示出不稳定的迹象。相反，随着淹没深度的增加，被动阻力和俯仰力矩减小，伴随着垂直力的增加。自由表面的起伏及其在流场中的干扰减少。随着攻角的增大,被动阻力和垂直力减小，而俯仰力矩增加，随着尾流方向的改变和自由表面复杂性的增加。这些结果为滑翔动力学提供了有价值的见解，为游泳者提供科学依据，以选择适当的淹没深度和迎角。
