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Seven-League Hydro Code (SLH)

An all Mach number code for fluid dynamics in astrophysics

Scientific area

Astrophysics, compressible fluid dynamics, implicit time-stepping, low Mach number scheme, iterative linear solvers.

Short description

SLH is a code designed for simulating the deep interior of stars using computational fluid dynamics. These regions of a star generally feature flows at low Mach numbers (< 0.01). Conventional schemes for fluid dynamics fail in this regime for reasons of efficiency and accuracy. This is why SLH uses implicit time-stepping and offers several discretizations suitable for all Mach numbers. The resulting large nonlinear system of equations (several 100 million unknowns for typical 3D problems) is solved using the Newton method and iterative linear solvers (BiCGSTAB, GMRES, multigrid). SLH shows good scaling behavior in strong scaling tests on JUQUEEN up to the full 458,752 cores. The largest problem size that was solved so far involved almost 10 billion unknowns on a 2688³ grid. SLH also features a flexible nuclear reaction network and a general equation of state, which are important to study instabilities and mixing processes in stars.

Seven-League Hydro CodeNuclear reactions in the accreted envelope of a white dwarf star, possible progenitor to a classical nova. The simulation was run on JUQUEEN as part of project HWB07. Image credit: Alejandro Bolaños (Würzburg University)


  • 458,752 cores (up to 1,835,008 threads) on BlueGene/Q (JUQUEEN)

Strong scaling of SLH on JUQUEENStrong scaling of SLH on JUQUEEN using the Taylor-Green vortex on a 1344³ grid. The code was run with one MPI process per core and 4 OpenMP threads per process.

Programming language and model

  • Fortran90 (+ some C)
  • MPI/OpenMP

Tested on platforms

  • BlueGene/Q
  • x86-64
  • IBM Power6

Application developers

Fabian Miczek, Friedrich Röpke, Philipp Edelmann, and others (see web page)


Friedrich Röpke,,
Philipp Edelmann,

(Text and images provided by the developers, see also the Technical Report FZJ-JSC-IB-2016-01)