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arXiv 2403.00482math.NAcs.NAphysics.flu-dyn
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三维非结构网格上可压缩流动的隐式高阶气体动理学格式 II:非定常流动

Implicit high-order gas-kinetic schemes for compressible flows on three-dimensional unstructured meshes II: unsteady flows

Yaqing Yang, Liang Pan, Kun Xu

AI总结:

针对非定常模拟受局部网格尺寸制约、全局时间步长过小的问题,提出两阶段三阶隐式时间精确 HGKS,并结合 WENO/HWENO 重构,在保持精度的同时提升大网格尺寸变化情形下的效率。

摘要:

在非定常流动模拟中,当局部网格尺寸变化很大时,全局时间步长会变得非常小。本文发展了一种隐式高阶气体动理学格式(HGKS),以消除非定常模拟中对时间步长的限制。为提高效率并保持高阶精度,提出了一种两阶段三阶隐式时间精确离散方法。在每个阶段,通过伪时间迭代获得隐式系统的人工稳态解。迭代中采用经典隐式方法求解非线性系统,包括下-上对称高斯-赛德尔(LUSGS)方法和广义最小残差(GMRES)方法。为实现空间精度,构造了同时具有非紧致和紧致重构的 HGKS。对于非紧致格式,使用加权本质无振荡(WENO)重构;对于紧致格式,由于需要同时更新单元平均流动变量及其导数,采用 Hermite WENO(HWENO)重构。借助两阶段时间离散,达到了预期的三阶时间精度。对于光滑流动,仅需单次人工迭代。对于均匀网格,与显式方法相比,当前隐式方法的效率显著提高。对于含间断的流动,与著名的 Crank-Nicholson 方法相比,当前格式中的虚假振荡得到了很好的抑制。人工迭代步数的增加会引入额外重构,并伴随计算效率的降低。总体而言,在网格尺寸变化很大的情况下,当前隐式方法相较显式方法带来了效率提升。

英文摘要:

For the simulations of unsteady flow, the global time step becomes really small with a large variation of local cell size. In this paper, an implicit high-order gas-kinetic scheme (HGKS) is developed to remove the restrictions on the time step for unsteady simulations. In order to improve the efficiency and keep the high-order accuracy, a two-stage third-order implicit time-accurate discretization is proposed. In each stage, an artificial steady solution is obtained for the implicit system with the pseudo-time iteration. In the iteration, the classical implicit methods are adopted to solve the nonlinear system, including the lower-upper symmetric Gauss-Seidel (LUSGS) and generalized minimum residual (GMRES) methods. To achieve the spatial accuracy, the HGKSs with both non-compact and compact reconstructions are constructed. For the non-compact scheme, the weighted essentially non-oscillatory (WENO) reconstruction is used. For the compact one, the Hermite WENO (HWENO) reconstruction is adopted due to the updates of both cell-averaged flow variables and their derivatives. The expected third-order temporal accuracy is achieved with the two-stage temporal discretization. For the smooth flow, only a single artificial iteration is needed. For uniform meshes, the efficiency of the current implicit method improves significantly in comparison with the explicit one. For the flow with discontinuities, compared with the well-known Crank-Nicholson method, the spurious oscillations in the current schemes are well suppressed. The increase of the artificial iteration steps introduces extra reconstructions associating with a reduction of the computational efficiency. Overall, the current implicit method leads to an improvement in efficiency over the explicit one in the cases with a large variation of mesh size.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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