Outflow boundaries play an important role in multiphase fluid dynamics simulations that involve transition between liquid and vapor phases. These flows are dominated by low Weber numbers and a sharp jump in pressure, velocity, and temperature. Inadequate treatment of these jumps at the outlet generates undesirable fluid disturbances that propagate upstream and lead to instabilities within the computational domain. To mitigate these disturbances, we introduce a forcing term that can be applied to incompressible Navier-Stokes equations to enforce stability in the numerical solution. The forcing term acts as a damping mechanism to control vortices that are generated by droplet/bubbles in multiphase flows, and is designed to be a general formulation that can be coupled with a fixed pressure outflow boundary condition to simulate a variety of multiphase flow problems. We demonstrate its applicability to simulate pool and flow boiling problems, where bubble-induced vortices during evaporation and condensation present a challenge at the outflow. Validation and verification cases are chosen to quantify accuracy and stability of the proposed method in comparison to established benchmarks and reference solutions, along with detailed performance analysis for three-dimensional simulations on leadership supercomputing platforms. Computational experiments are performed using Flash-X, which is a composable open-source software instrument designed for multiscale fluid dynamics simulations on heterogeneous architectures.

翻译：出流边界在涉及液-气相变的的多相流体动力学模拟中起着重要作用。这类流动受低韦伯数主导，并伴随压力、速度和温度的尖锐跳跃。若出口处未能妥善处理这些跳跃，将产生向上游传播的流体扰动，导致计算域内的不稳定。为抑制此类扰动，我们提出一种可施加于不可压纳维-斯托克斯方程的强迫项，用以增强数值解的稳定性。该强迫项作为阻尼机制控制多相流中液滴/气泡生成的涡旋，其通用公式可耦合固定压力出流边界条件，模拟多种多相流问题。我们通过池沸腾与流动沸腾算例验证其适用性——这类问题中，蒸发与冷凝过程的气泡诱导涡旋对出流边界构成挑战。通过对比基准算例与参考解，选取验证与确认案例量化所提方法的精度与稳定性，并详细分析在领导级超级计算平台上进行三维模拟的性能。计算实验基于闪速-X开源可组合软件开展，该软件专为异构架构下的多尺度流体动力学模拟设计。