DLBFoam: An open-source dynamic load balancing model for fast reacting flow simulations in OpenFOAM

Computational load imbalance is a well-known performance issue in multiprocessor reacting flow simulations utilizing directly integrated chemical kinetics. We introduce an open-source dynamic load balancing model named DLBFoam to address this issue within OpenFOAM, an open-source C++ library for Computational Fluid Dynamics (CFD). Due to the commonly applied operator splitting practice in reactive flow solvers, chemistry can be treated as an independent stiff ordinary differential equation (ODE) system within each computational cell. As a result of the highly non-linear characteristics of chemical kinetics, a large variation in the convergence rates of the ODE integrator may occur, leading to a high load imbalance across multiprocessor configurations. However, the independent nature of chemistry ODE systems leads to a problem that can be parallelized easily (called an embarrassingly parallel problem in the literature) during the flow solution. The presented model takes advantage of this feature and balances the chemistry load across available resources. Additionally, a reference mapping model is utilized to further speed-up the simulations. When DLBFoam it utilized with both these features enabled, a speed-up by a factor of 10 is reported for reactive flow benchmark cases. To the best of our knowledge, this model is the first open-source implementation of chemistry load balancing in the literature.

在多处理器反应流模拟中，利用直接集成化学动力学所导致的计算负载不均衡是一个众所周知的问题。本研究提出了一种名为DLBFoam的开源动态负载均衡模型，旨在解决OpenFOAM（一款开源的用于计算流体动力学（CFD）的C++库）中的该问题。鉴于在反应流求解器中广泛应用的算子分裂惯例，化学动力学可以被视为每个计算单元中独立的刚性常微分方程（ODE）系统。由于化学动力学的高度非线性特性，ODE积分器的收敛速率可能出现较大差异，从而导致多处理器配置中的负载不均衡。然而，化学ODE系统的独立性导致了一个易于并行化的问题（文献中称为令人尴尬的并行问题）在流求解过程中。所提出的模型充分利用这一特性，平衡可用资源上的化学负载。此外，还采用了一种参考映射模型以进一步加速模拟过程。当DLBFoam结合这两种特性使用时，据报道在反应流基准案例中实现了10倍的速度提升。据我们所知，该模型是文献中第一个开源的化学负载均衡实现。