Simulation of Multi-Scale Free Surfaces within Gas-Liquid flows using Combined Particle and Grid Methods

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  • ISHII Eiji
    株式会社 日立製作所 機械研究所
  • ISHIKAWA Toru
    株式会社 日立製作所 オートモーティブシステムグループ
  • TANABE Yoshiyuki
    株式会社 日立製作所 オートモーティブシステムグループ

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Other Title
  • 粒子法とグリット法の結合によるマルチスケール気液界面解析
  • 粒子法とグリッド法の結合によるマルチスケール気液界面解析
  • リュウシホウ ト グリッドホウ ノ ケツゴウ ニ ヨル マルチスケールキエキ カイメン カイセキ

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Description

Gas-liquid flows usually include multi-scale free surfaces, for example, fuel sprays used for automobile engines become liquid films at the outlet of fuel injectors, and then the liquid films break up into droplets. Fluid flow with free surfaces, like the liquid films, are mainly simulated using grid methods, where the front of the free surface is directly captured on regular, fixed grids that cover both liquid and gas domains. In these methods, however, free surfaces are sometimes lost due to numerical diffusion in case the scale of the free surfaces becomes smaller than the grid size. Particle methods can avoid the occurrence of such the unreal loss of free surfaces. The particle methods treat the free surfaces as groups of particles that move in a pattern based on a Lagrangian description. To simulate the multi-scale free surfaces, we have developed a hybrid particle/grid method where the free surfaces within a sub-grid region are simulated with particles located near the liquid interfaces. Velocities determined using the particle method are combined with those obtained from the grid method. However, the interaction between gas and liquid still depends on the grid size because the gas regions within the sub-grid regions were calculated by the grid method. Accordingly, the present method adopts a two-particle model as the particle method; that is, the free surfaces within the sub-grid region are simulated with two types of particles, one for the gas and the other for the liquid. The sub-grid regions are determined by using the volume fraction of liquid calculated using the grid method, and then the two-particle model is applied to the sub-grid regions. We will verify the new method by applying it to prediction of large deformation in free surfaces (the Rayleigh-Taylor instability) and to the fragmentation of a water column. The predicted deformed shape of the water column shows good agreement with measurements reported by Koshizuka et al.

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