The paper presents high-order accurate, energy-, and entropy-stable discretizations constructed from summation-by-parts (SBP) operators. Notably, the discretizations assemble global SBP operators and use continuous solutions, unlike previous efforts that use discontinuous SBP discretizations. Derivative-based dissipation and local-projection stabilization (LPS) are investigated as options for stabilizing the baseline discretization. These stabilizations are equal up to a multiplicative constant in one dimension, but only LPS remains well conditioned for general, multidimensional SBP operators. Furthermore, LPS is able to take advantage of the additional nodes required by degree 2p diagonal-norms, resulting in an element-local stabilization with a bounded spectral radius. An entropy-stable version of LPS is easily obtained by applying the projection on the entropy variables. Numerical experiments with the linear-advection and Euler equations demonstrate the accuracy, efficiency, and robustness of the stabilized discretizations, and the continuous approach compares favorably with the more common discontinuous SBP methods.Mathematics Subject Classification (2010) 65M06 · 65M60 · 65M70 · 65M12
IntroductionHigh-order discretizations have been put forward as a possible means of improving the efficiency of computational fluid dynamics (CFD) simulations. The arguments in favor of high-order discretizations include both improved accuracy-per-degree-of-freedom as well as better cache usage on current and future architectures. Despite these potential advantages, the use of high-order CFD remains uncommon in industry. Mesh generation of curved This is a pre-print of an article published in The Journal of Scientific Computing. The final authenticated version is available online at: https://doi.bustness: high-order discretizations have inherently less numerical dissipation, which makes them prone to instabilities, particularly for under-resolved flows.Entropy stability offers one promising avenue for constructing robust, high-order CFD methods. This is not a new idea. For example, over thirty years ago, Hughes et al. [36] presented a finite-element discretization of the compressible Navier-Stokes equations that satisfied the second-law of thermodynamics. And in 1999, Barth [2] extended this work to cover Galerkin-least-squares stabilizations and discontinuous Galerkin (DG) schemes. However, these early examples make the assumption that the integrations present in the finite-element semi-linear forms are exact. Exact integration is not possible, in general, for the Euler and Navier-Stokes equations, so these schemes must rely on potentially costly "over-integration" in practice. Even then, the discrete schemes are not provably stable and may fail.In light of the above, there has been growing interest in semi-discrete and fully-discrete high-order schemes that are provably entropy stable. Fisher's thesis [24] represented a seminal contribution in this direction -see also [26] and [25]. He showed that summationby-parts (SBP) fini...