Adaptive Mesh Refinement and Continuum Surface Force Method for Complex Two-Phase Flows
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摘要:
针对具有复杂气液界面拓扑变化的两相流动问题,构建一种能够兼顾计算效率与界面解析精度的数值模拟方法. 首先,采用具有树状数据结构的四叉树/八叉树笛卡尔网格进行空间离散,利用其层级结构实现动态网格自适应;其次,在自适应网格框架下实现连续表面力(CSF)模型,通过对体积分数进行两次卷积模糊化处理,平滑地将表面张力分布至界面邻域,并结合分段线性界面重构技术准确追踪气液界面;随后,建立网格加密准则,同时考虑基于流场速度小波分析的离散误差和界面处的曲率分布,以实现对流场剧烈变化区域及相界面的动态加密;最后,通过经典气液两相流算例验证算法的准确性与可靠性. 研究表明:在表面张力Laplace律验证中,采用界面曲率为细化准则时,其内外压力差计算误差仅为3.0%,远优于基于体积分数准则的7.5%~24.0%误差,且精度与均匀细网格相当;所提方法较均匀细网格可降低约一个数量级的计算耗时;在表面张力波计算中,数值解与正则模态理论解的均方根误差可低至10−5量级;在双元液滴正碰模拟中,准确复现了实验中观测到的哑铃形与菱形变形序列,并捕捉到气膜破裂及微小气泡形成等复杂界面拓扑演化细节.
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关键词:
- 两相流动 /
- 四叉树/八叉树数据结构 /
- 连续表面力方法 /
- 自适应网格
Abstract:To address two-phase flow problems with complex gas-liquid interface topology variation, a numerical simulation method capable of balancing computational efficiency and interface resolution accuracy was proposed. First, quadtree/octree Cartesian meshes with tree data structures were employed for spatial discretization. Adaptive mesh refinement was developed by leveraging the mesh’s hierarchical structures. Second, the continuum surface force (CSF) model was implemented within the adaptive mesh framework. By applying double convolution blurring to the volume fraction, the surface tension was smoothly distributed to the interface neighborhood, and the piecewise linear interface reconstruction technique was utilized to track the gas-liquid interface accurately. Subsequently, a mesh refinement criterion was established, and both the discrete error based on wavelet analysis of flow field velocity and the interface curvature distribution were considered, thereby achieving dynamic refinement in regions with sharp flow field variations and phase boundaries. Finally, the accuracy and reliability of the algorithm were validated through numerical examples of classic gas-liquid two-phase flow. The results show that in the verification of the Laplace law of surface tension, when the interface curvature is adopted as the refinement criterion, the computational error of internal and external pressure difference is only about 3.0%, which is significantly superior to the error range from 7.5% to 24% when using the volume fraction as the criterion, and its accuracy is consistent with that of uniform fine meshes. The proposed method can reduce the computational time consumption by approximately one order of magnitude compared with uniform fine meshes. In the numerical examples of surface tension waves, the root mean square error between the numerical solution and the theoretical solutions of regular modal can be reduced to the order of 10−5. In the simulation of a head-on collision between binary droplets, the experimentally observed dumbbell-shaped and diamond-shaped deformation sequences are reproduced, and the complex interface topology evolution details such as gas film rupture and the formation of tiny bubbles are captured.
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表 1 二维液滴压力差
Table 1. Pressure difference in two-dimensional droplet
层格层级 细化准则 压力差 压力差误差/% 5~8 体积分数 2.48 24.0 6~8 体积分数 2.47 23.5 7~8 体积分数 2.15 7.5 5~8 曲率 2.06 3.0 表 2 三维液滴压力差
Table 2. Pressure difference in three-dimensional droplet
网格层级与
细化准则5~8,
f6~8,
f7~8,
f5~8,
$\kappa $压力差 4.43 4.45 4.41 3.93 误差/% 21.5 22.5 20.5 3.5 表 3 网格数与CPU时间
Table 3. Number of meshes and CPU time
计算模型 网格层级 网格数 CPU 时间/s 二维 5~8 5194 2.92 二维 8~8 65536 14.48 轴对称 5~8 3070 2.50 轴对称 8~8 65536 15.97 三维 5~8 385064 940.71 三维 8~8 16777216 6417.03 -
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