Weighted nonlinear compact schemes are ideal for simulating compressible, turbulent flows because of their nonoscillatory nature and high spectral resolution. However, they require the solution to banded systems of equations at each time-integration step or stage. We focus on tridiagonal compact schemes in this paper. We propose an efficient implementation of such schemes on massively parallel computing platforms through an iterative substructuring algorithm to solve the tridiagonal system of equations. The key features of our implementation are that it does not introduce any parallelization-based approximations or errors and it involves minimal neighbor-toneighbor communications. We demonstrate the performance and scalability of our approach on the IBM Blue Gene/Q platform and show that the compact schemes are efficient and have performance comparable to that of standard noncompact finite-difference methods on large numbers of processors (∼ 500, 000) and small subdomain sizes (four points per dimension per processor).
Introduction.Weighted, nonlinear compact schemes use the adaptive stencil selection of the weighted, essentially nonoscillatory (WENO) [29,46] schemes to yield essentially nonoscillatory solutions with high spectral resolution; they are thus ideal for simulating compressible, turbulent flows. Notable efforts include weighted compact nonlinear schemes (WCNSs) [13,14,52,50], hybrid compact-ENO/WENO schemes [6,5,38,42], weighted compact schemes (WCSs) [30,33,51], compact-reconstruction WENO (CRWENO) schemes [19,22,18,20], and finite-volume compact-WENO (FVCW) schemes [25]. These schemes show a significant improvement in the resolution of moderate-and small-length scales compared with the resolution of the standard WENO schemes of the same (or higher) order and were applied to the simulation of compressible, turbulent flows. WCNSs [14,52,50] result in a system of equations with a linear left-hand side that can be prefactored. This is a substantial advantage; however, the spectral resolution of these schemes is only marginally higher than that of the WENO scheme. The hybrid compact-WENO, WCS, CRWENO, and FVCW schemes have a significantly higher spectral resolution, as demonstrated by both linear and nonlinear spectral analyses [38,20]. They result in solution-dependent systems of equations at each time-integration step or stage. Tests have shown that on