4.4.5 Hydrodynamics (Roe solver)

4.4.5.1 rhd_hyd_gravcorr_p01

(``rhd hydrodynamics gravitation correction parameter 01'') in rhd_hyd_module.F90.
Category: selection of approximation.
This parameter controls the way the Roe solver handles the source terms due to gravity. A different choice results in different simulation results and not just in slightly faster (or slower) code. The problem is that the original Roe solver interpretes the pressure gradient in a hydrostatic stratification a fluctuation due to shock waves. In case of strong stratification this can lead to weird effects. With activated correction the Roe solver treats only the deviations from a hydrostatic stratification as due to waves (or shocks). Several correction formulas have been tried. The latest is the recommended default. Values:

• 0: No pressure correction terms in Roe solver.
• 1: Simple correction with rhomean, no new average pressure.
• 2: Simple correction with rhomean, new average pressure.
• 3: Correction with local rho, limited, new average pressure.
• 4: Correction with local rho, new (different formula) average pressure.
• 5: (default) Correction with local rho, new limit, new average pressure.
• 6: Modification of 5 with different geometry factors in case of non-equidistant grid.

4.4.5.2 rhd_hyd_entropyfix_p01

(``rhd hydrodynamics entropy fix parameter 01'') in rhd_hyd_module.F90.
Category: performance enhancement.
The entropy fix can be done in one of two ways to get optimum performance (with essentially the same results). Values:

• 0: (default) ``if...then...else'' construction
• 1: use a mask and the signum function

4.4.5.3 rhd_hyd_upwind_p01

(``rhd hydrodynamics upwind parameter 01'') in rhd_hyd_module.F90.
Category: performance enhancement.
The determination of the upwind direction can be done in one of two ways to get optimum performance (with essentially the same results). Values:

• 0: (default) ``if...then...else'' construction
• 1: use a mask and the signum function

4.4.5.4 rhd_roe1d_flux_l01

(``rhd roe 1 dimension flux loop 01'') in rhd_hyd_module.F90.
Category: performance enhancement.
This switch allows to choose between various ways of computing the upwind-centered Roe states. Values:

• 0: Use upwind-index arrays in all Roe-state computations. Do it in one step (old default).
• 1: Use if-then-else-constructs in all Roe-state computations. Do it in one step (default, recommended).
• 2: Use upwind-index arrays in all Roe-state computations. Do it in two steps.
• 3: Use if-then-else-constructs in all Roe-state computations. Do it in two steps.

4.4.5.5 rhd_bound_t01

(``rhd bound timing 01'') in rhd_hyd_module.F90.
Category: additional output.
Produce timing information for ``inner boundary'' routine (central potential) or lower and upper boundary routines (constant gravitation). It can be used together with OpenMP. Values:

• undefined: (default) no timing information.
• defined: call subroutines to measure elapsed time.

4.4.5.6 rhd_roe1d_flux_t01

(``rhd roe 1 dimension flux timing 01'') in rhd_hyd_module.F90.
Category: additional output.
Produce timing information for the routine which computes the Roe fluxes. It should not be used in conjunction with OpenMP. Values:

• undefined: (default) no timing information
• defined: call subroutines to measure elapsed time

4.4.5.7 rhd_roe1d_step_t01

(``rhd roe 1 dimension step timing 01'') in rhd_hyd_module.F90.
Category: additional output.
Produce timing information for the routine which performs the Roe step. It should not be used in conjunction with OpenMP. Values:

• undefined: (default) no timing information
• defined: call subroutines to measure elapsed time