基于流固耦合的氦气囊非稳定形态机理分析

Unstable morphology mechanism analysis of helium bag based on two-way fluid-structure coupling

为了揭示飞艇内置氦气囊在非稳定状态下的形态变化机理,建立了单个氦气囊模型,基于ANSYS的瞬态动力分析和CFX的多场耦合分析,考虑空气与氦气密度差导致的浮力效应,进行空气和氦气流体及柔性囊体的多场耦合分析.首先基于囊体无应力态进行充气模拟得到初始充气平衡形态,校验数值模拟方法的正确性.然后通过控制氦气排气量模拟氦气囊在0°、10°、20°、30°仰角以及充盈度分别为100%、90%、80%、70%、60%时的形态,并进行变形、应力特征分析.数值结果表明:在仰角为0°时,随充盈度减小,囊体底部约1/3区域发生形态失稳,呈环向均匀小凹陷模态,且向顶部扩展,环向贯通为大凹陷;当有仰角时,凹陷先发生于下腹部,环向非对称,且随仰角增大,下腹部凹陷向顶部扩大.

In order to reveal the morphological transforming mechanism of the airship’s helium bag bedded-inside the envelope under an unstable state, a single helium bag model was established. Based on the transient dynamic analysis of ANSYS and the multi-phase coupling analysis of CFX, considering the buoyancy effect caused by the density difference between air and helium, a multi-phase coupling analysis of air, helium and flexible membrane bag has been carried out. Firstly, the initial inflated equilibrium shape was commutated from the unstressed geometry of the helium bag by inflating simulation, and the buoyancy and gravity equilibrium and deformation validated the numerical simulation method. Then, the helium gas flow control method was employed to simulate the helium bag at elevation angles of 0, 10, 20, 30 degrees and at filling percentages of 100, 90, 80, 70 and 60 respectively. The numerical results show that when the elevation angle is zero, approximately 1/3 of the bottom of the helium bag becomes unstable as the filling percentage decreases. The circular uniform sag modes were observed to extend toward the top and a large sag in the circumferential direction. When there is an elevation angle, the sag first occurs in the lower part and exhibits circumferential asymmetry. With the increase of the elevation angle, the sag in the lower part expands toward the top.