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Spatial-Temporal Adaptive-Order Positivity-Preserving WENO Finite Difference Scheme with Relaxed CFL Condition for Euler Equations with Extreme Conditions
Jia-Le Li, Wai-Sun Don, Cai-Feng Wang and Bao-Shan Wang

Adv. Appl. Math. Mech. DOI: 10.4208/aamm.OA-2023-0306

Publication Date : 2025-01-09

  • Abstract

In extreme scenarios, classical high-order WENO schemes may result in non-physical states. The Positivity-Preserving Limiter (PP-Limiter) is often used to ensure positivity if $\CFL \leq 0.5$ with a third-order TVD Runge-Kunta (RK3) scheme. This study proposes two novel conservative WENO-Z methods: AT-PP and AO-PP to improve efficiency with $0.5 < \CFL < 1$ if desired. The AT-PP method detects negative cells after each RK3 stage posteriori and computes a new solution with the PP-Limiter ($\CFL < 0.5$) for that step. The AO-PP method progressively lowers the WENO operator's order and terminates with the first-order HLLC solver, proven positivity-preserving with $\CFL<1$, only at negative cells at that RK3 stage. A single numerical flux enforces conservation at neighboring interfaces. Extensive 1D and 2D shock-tube problems were conducted to illustrate the performance of AT-PP and AO-PP with $\CFL = 0.9$. Both methods outperformed the classical PP-Limiter in accuracy and resolution, while AO-PP performed better computationally in some cases. The AO-PP method is globally conservative and accurate, adaptiveness, and robustness while resolving fine-scale structures in smooth regions, capturing strong shocks and gradients with ENO-property, improving computational efficiency, and preserving the positivity, all without imposing a restrictive limit on the CFL condition.

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