交错型CPR方法的保正实现策略及其对比研究

Positivity-preserving strategies and their comparision based on staggered CPR methods

  • 摘要: 计算流体力学方法在模拟涉及强间断、极低密度和极低压力的问题时容易出现因数值误差导致的负密度或负压力,从而导致计算失败,这点对于高阶精度格式尤为突出。为了解决该问题,学界发展了保正限制器,并重点针对其在高阶有限元算法中的应用进行了研究。但是,对于混合CPR/CNNW(correction procedure via reconstruction/compact non-uniform nonlinear weighted)格式,如何保证在从求解点向通量点插值的过程中,通量点上的数值始终满足保正条件,目前仍缺乏深入的研究。本文针对混合CPR/CNNW格式中的通量点保正问题,分别基于保正限制器和一阶迎风插值发展了两种保正策略。理论推导了适用于混合CPR/CNNW格式的平均值保正方法,并设计了在多级RK(multi-stage Runge-Kutta)时间推进中进行平均值保正的方法。在此基础上,对两种保正策略在多种间断问题中的表现进行了数值测试,重点比较两种保正策略的分辨率、鲁棒性和计算效率。数值测试表明,本文提出的保正策略能够有效确保计算不崩溃;其中,fpupwind策略在马赫数2 000射流问题中,将CPU时间降低了约55%,并允许使用更大的时间步长,显著提升了计算效率。

     

    Abstract: High-order accurate algorithms often encounter numerical instabilities, such as negative density or pressure, when simulating flow fields with strong discontinuities, extremely low density, or low pressure. To maintain numerical robustness while preserving high-order accuracy, significant research efforts have been devoted to positivity-preserving limiters, particularly for high-order finite element algorithms. However, existing positivity-preserving limiters predominantly focus on ensuring positivity at solution points instead of flux points. In the hybrid correction procedure via reconstruction/compact non-uniform nonlinear weighted (CPR/CNNW) scheme, there is still a lack of in-depth research regarding the positivity preservation at flux points interpolated from solution points. In this paper, we proposed two positivity-preserving strategies for the hybrid CPR/CNNW scheme using positivity-preserving limiters and a first-order upwind method to enforce positivity constraints at flux points. Furthermore, we developed a positivity-preserving method for cell averages within the hybrid CPR/CNNW scheme, incorporating a multi-stage Runge-Kutta time integration. The two positivity-preserving strategies have been validated by numerical simulations of various problems involving discontinuities, focusing on the resolution, efficiency and robustness of the two strategies. The results show that both strategies can prevent computational crashes. In particular, the fpupwind strategy reduces CPU time by approximately 55% for the Mach 2 000 jet problems, respectively, while allowing for a larger time step size, thereby significantly improving computational efficiency.

     

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