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arXiv 1905.02484physics.flu-dyn
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不可压缩流体中运动物体上力的分解

Decomposition of the forces on a body moving in an incompressible fluid

W R Graham

摘要:

在分析作用在运动物体上的流体力时,一种自然的方法是寻找粘性分量和“无粘性”余数。将速度场分解为无旋部分和有旋部分,并相应地分配合力也很有吸引力。“无旋”的合成物可以被认为是经典的“附加质量”,但其余的“旋转”的合成物似乎与旋转速度场的物理解释不一致(因为它是由物体静止时的流体涡度引起的)。这里提出的替代方案将无粘性合成物分成无疑是由于问题的独立方面造成的分量:“对流”和“加速”。前者与压力场有关,压力场将在无粘性流中产生,(瞬时)与真实速度相同,并且与物体的速度参数--角和平移--不变。后者对应于当物体在静止流体中以其给定的角速度和平移速度的变化率从静止加速时产生的压力。它们让人想起附加质量力的合力,但比附加质量力和附加质量力矩的表达式更简单,更接近标准刚体惯性公式。最后,由粘性引起的合力还包括压力的贡献。它的存在是必要的,以满足方程的压力场,它以前已被确认的背景下,“过剩”滞流点压力。然而,它的存在似乎还没有得到广泛的赞赏。

英文摘要:

In analysing fluid forces on a moving body, a natural approach is to seek a component due to viscosity and an `inviscid' remainder. It is also attractive to decompose the velocity field into irrotational and rotational parts, and apportion the force resultants accordingly. The `irrotational' resultants can then be identified as classical `added mass', but the remaining, `rotational', resultants appear not to be consistent with the physical interpretation of the rotational velocity field (as that arising from the fluid vorticity with the body stationary). The alternative presented here splits the inviscid resultants into components that are unquestionably due to independent aspects of the problem: `convective' and `accelerative'. The former are associated with the pressure field that would arise in an inviscid flow with (instantaneously) the same velocities as the real one, and with the body's velocity parameters --- angular and translational --- unchanging. The latter correspond to the pressure generated when the body accelerates from rest in quiescent fluid with its given rates of change of angular and translational velocity. They are reminiscent of the added-mass force resultants, but are simpler, and closer to the standard rigid-body inertia formulae, than the developed expressions for added-mass force and moment. Finally, the force resultants due to viscosity also include a contribution from pressure. Its presence is necessary in order to satisfy the equations governing the pressure field, and it has previously been recognised in the context of `excess' stagnation-point pressure. However, its existence does not yet seem to be widely appreciated.

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