Development of Numerical Simulator of Ice-accretion on a Body in Oscillation

基于计算流体力学的数值模拟器已被开发出来，它可以预测振动状态下物体表面上的结冰形状。在本模拟器中，我们采用了BASIC程序中描述多相流模型的欧拉方法，这是因为这种方法在模拟振荡物体周围的流动方面具有优势。采用双流体Saffman方程作为过冷大气的模型，考虑Naver-Stokes溶液的势流和粘性流作为载流相。(1)摆动圆柱面局部撞击效率的预测通过求解Saffman方程，在任意平移有循环的圆柱体的势流场下，得到了在一定的斯托克斯数范围内俯仰或垂荡振动时圆柱面的局部撞击效率(质量通量分布)。我们还发现了Uns…(2)粘性流动中凝结冰形状的预测。通过耦合N-S方程，对硬结冰在圆柱体上的吸积进行了数值模拟。在欧拉方法中，硬雾化过程有两种选择：一种是液滴来流速度的选择，另一种是冰晶生长方向的选择。计算结果表明，每种方案都给出了不同的硬边形状。由于局部撞击效率是硬冰生长过程中最重要的影响因素，因此欧拉模型比拉格朗日模型具有更好的预测各种冰形状的优势。(3)基于势流模型的Saffman方程密度场的解析解，得到滞流区密度场随Stokes数的变化关系。这个表达式是Michael在1968年的结果的推广。较少

Numerical simulator has been developed based on Computational Fluid Dynamics appraoch, which is possible to predict the shape of accreted ice on a body surface in oscillation. In the present simulator, we employ Eulerian approach with 2-fluid description of multi-phase flow model in the basic codes, because this approach has the advantage in simulating flows around an oscillating body. The 2-fluid Saffman equation is used as a model of super-cooled atmosphere Then, we consider potential flow and viscous flow of Naver-Stokes solution as the carrier phase. The present simulator makes the following facts clear.(1) Prediction of local impingement efficiency along an oscillating cylinderBy solving the Saffman equation under the potential flow field of a circular cylinder with circulation in arbitrary translation, local impingement efficiency (distribution of mass flux) along the cylinder surface in pitching or heaving oscillation is obtained in some values of Stokes number. We also find uns … More teady behaviour of density field of water droplets around the cylinder by the visualization of computational results.(2) Prediction of the shape of accreted ice in viscous flowSimulation of hard-rime accretion on a circular cylinder is performed under the condition (Re=10^4, St=10) by coupling the Navier-Stokes equations. In Eulerian approach, there are two kinds of option for the process of hard-rime growth : one is choice of incoming velocity of droplet, the other is the direction of ice-growth. Computational results show each option gives the different shape of hard-rime. Since local impingement efficiency has the most important effect in the process of hard-rime growth, the present results suggest that Eulerian model has advantage of predicting wide variety of ice shapes rather than Lagrangian approach.(3) Density field of Saffman equationDensity field in the stagnation region is obtained analytically as the function of Stokes number based on potential flow model. This expression is a generalization of Michael's result in 1968. Less