The air layer drag reduction (ALDR) of an axisymmetric body in oscillatory motions is investigated in this paper with open source toolbox OpenFOAM. The unsteady Reynolds-averaged Navier-Stokes (URANS) equations are used to determine the viscous flow and the volume of fluid (VOF) model is adopted to capture the interface of the air-water two-phase flow. The k − ε turbulence model is adopted to simulate the turbulence. The dynamic mesh technique is applied to model the movement of the axisymmetric body. Firstly, the ALDR results are validated by the experimental data. Then, the effects of the movements of the body on the drag reduction during the ALDR state are investigated. Two representative kinds of movements are considered, namely, the pitch and the heave. The numerical results show that the drag reduction varies during the movements and the average drag reduction rates will be reduced. The variation of the drag reduction is related to the morphological change of the air layer. The heave motion is more likely to reduce the effects of the ALDR than the pitch motion. For both oscillatory motions, the large motion amplitude and the low motion period are not conductive to improving the effects of the ALDR. The effects of the oscillatory motion on the ALDR are more sensitive at high water speeds than at low water speeds. Besides, increasing the air flow ratio can be considered as one way to improve the effects of the ALDR.

本文使用开源工具箱 OpenFOAM 研究了摆动运动中轴对称体的空气层减阻 (ALDR)。使用非定常雷诺平均纳维-斯托克斯 (URANS) 方程确定粘性流，并采用流体体积 (VOF) 模型捕获气水两相流的界面。该的k - ε采用湍流模型来模拟湍流。应用动态网格技术来模拟轴对称体的运动。首先，ALDR结果得到了实验数据的验证。然后，研究了身体运动对 ALDR 状态期间减阻的影响。考虑了两种有代表性的运动，即俯仰和升沉。数值结果表明，减阻在运动过程中发生变化，平均减阻率会降低。减阻的变化与空气层的形态变化有关。与俯仰运动相比，升沉运动更有可能减少 ALDR 的影响。对于这两种振荡运动，大的运动幅度和低的运动周期都不利于提高 ALDR 的效果。振荡运动对 ALDR 的影响在高水速下比在低水速下更敏感。此外，增加空气流量比可以被认为是提高 ALDR 效果的一种方式。