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首页> 外文期刊>Journal of Computational Physics >Mesh refinement algorithms in an unstructured solver for multiphase flow simulation using discrete particles
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Mesh refinement algorithms in an unstructured solver for multiphase flow simulation using discrete particles

机译：非结构化求解器中的网格细化算法，用于使用离散粒子进行多相流模拟

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This study developed spray-adaptive mesh refinement algorithms with directional sensitivity in an unstructured solver to improve spray simulation for internal combustion engine application. Inadequate spatial resolution is often found to cause inaccuracies in spray simulation using the Lagrangian-Eulerian approach due to the over-estimated diffusion and inappropriate liquid-gas phase coupling. Dynamic mesh refinement algorithms adaptive to fuel sprays and vapor gradients were developed in order to increase the grid resolution in the spray region to improve simulation accuracy. The local refinement introduced the coarse-fine face interface that requires advanced numerical schemes for flux calculation and grid rezoning with moving boundaries. To resolve the issue in flux calculation, this work implemented the refinement/coarsening algorithms into a collocated solver to avoid tedious interpolations in solving the momentum equations. A pressure correction method was applied to address unphysical pressure oscillations due to the collocation of pressure and velocity. An edge-based algorithm was used to evaluate the edge-centered quantities in order to account for the contributions from all the cells around an edge at the coarse-fine interface. A quasi-second-order upwind scheme with strong monotonicity was also modified to accommodate the coarse-fine interface for convective fluxes. To resolve the issue related to grid rezoning, rezoning was applied to the initial baseline mesh only and the new locations of the refined grids were obtained by interpolating the updated baseline mesh. The time step constraints were also re-evaluated to account for the change resulting from mesh refinement. The present refinement algorithm was used in simulating fuel sprays in an engine combustion chamber. It was found that the present approach could produce the same level of results as those using the uniformly fine mesh with substantially reduced computer time. Results also showed that this approach could alleviate the artifacts related to the Lagrangian discrete modeling of spray drops due to insufficient spatial resolution.
机译：这项研究开发了一种在非结构化求解器中具有方向敏感性的喷雾自适应网格细化算法，以改进用于内燃机的喷雾模拟。由于过高估计的扩散和不适当的液相-气相耦合，经常发现空间分辨率不足会导致使用拉格朗日-欧拉方法进行喷雾模拟时出现误差。开发了适用于燃料喷雾和蒸汽梯度的动态网格细化算法，以提高喷雾区域中的网格分辨率，从而提高模拟精度。局部改进引入了粗细面接口，该接口需要用于流动通量计算和网格重分区的高级数值方案。为了解决通量计算中的问题，这项工作将细化/粗化算法应用到并置的求解器中，以避免在求解动量方程时进行繁琐的插值。应用压力校正方法来解决由于压力和速度并置导致的非物理压力振荡。基于边缘的算法用于评估以边缘为中心的量，以便考虑粗细界面处边缘周围所有像元的贡献。还修改了具有强单调性的准二阶迎风方案，以适应对流通量的粗细界面。为了解决与网格重新分区有关的问题，仅将重新分区应用于初始基线网格，并通过对更新的基线网格进行插值来获得精炼网格的新位置。还重新评估了时间步长约束，以说明网格细化导致的更改。本改进算法用于模拟发动机燃烧室中的燃料喷雾。已经发现，本方法可以产生与使用均匀精细的网格的结果相同水平的结果，同时大大减少了计算机时间。结果还表明，由于空间分辨率不足，该方法可以减轻与拉格朗日离散液滴建模有关的伪影。

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