Optional parameters can be specified in a list at the end of the input file.
This is done by specifying the name of the parameter, and its value on the same line.
The value must be in floating point decimal form, and must line up with the header: VALUE
The listed parameters and their values are output at the start of the run, providing the user with a check of the values read in.
The following is a list of all of the available optional parameters sorted by function with the typical values used for each. Click on the parameter names for complete descriptions. An alphabetized list is also included below for convenience.
Hover over a parameter for a short definition or CLICK on it to be taken to it's listing below.
OPTIONAL PARAMETERS BY FUNCTION:
DES: Detached Eddy Simulation
The DES is implemented in the NSU3D version nsu3d.4.9.m.alpha8. Right now the DES is based on the Spalart-Allmaras turbulence model. Set the input parameter ITURB to be 7 to run a SA-DES case. The optional input parameter ISARC need to be 1. Three optional input parameters also need to be set:
DISCRETIZATION TYPE (CONVECTIVE)
IFLUX_TYPE: Specifies the type of flux or dissipation for the spatial discretization scheme. Currently 3 options are implemented:
For Navier-Stokes flows, IFLUX_TYPE = 0 is recommended, as there are still issues of accuracy with the other schemes.
For Euler (inviscid) flows, IFLUX_TYPE = 1 is relatively robust for supersonic flows especially when using a limiter (see ILIM_TYPE).
IGRAD_TYPE: Defines the values used in gradient reconstruction with IFLUX_TYPE=1,2 (IGRAD_TYPE is inactive for IFLUX_TYPE=0)
IFREEZE_GRAD: Used to enable freezing of gradient calculation within the stages of the Runge-Kutta multi-stage scheme. This speeds up execution, but may be less stable. Gradients are recomputed at each time-step in the first stage of the Rung-Kutta scheme, so the final converged result will be identical regardless of the value of IFREEZE_GRAD
ILIM_TYPE: Select Type of Limiter for Upwind Reconstruction Schemes (IFLUX_TYPE=1,2...Not active for IFLUX_TYPE=0)
FK_LIMIT: Parameter in Venkataskrishnan TVB limiter. Low values tend to weaker enforcement of monotonicity, high values tend toward original monotone limiter.
IFREEZE_LIM: Specifies if and how to freeze limiters (for IFLUX_TYPE=1 or 2 only, inactive for IFLUX_TYPE=0) Convergence to steady-state can be disrupted by limiters which switch back and forth at each iteration. Freezing these limiters may enable or enhance otherwise poor convergence, but the final steady-state result may depend on the manner in which the limiters have been frozen and the convergence history (i.e. a restart solution may converge to slightly different results). In general these differences should be acceptably small.
NFREEZE_LIM: Controls limiter freezing. Freeze limiters (IFREEZE_LIM=1) or begin freezing limiters (IFREEZE_LIM=2,3) after NFREEZE_LIM cycles. Only active for IFREEZE_LIM > 0
BIHFACTR: is a factor which scales the linearization of the biharmonic dissipation terms in the Jacobian.
Generally, a 1st order Jacobian is used for the point or line implicit solution algorithm.
When using a biharmonic (artificial) dissipation scheme, there is no simple correspondance between the linearization of these terms and a 1st order (2nd difference dissipation) Jacobian. Therefore, we use the nearest neighbor entries from the biharmonic construction, and scale these by the factor BIHFACTR.
BIHFACTR = 20.0 : Standard Value. Higher value produces more diagonally dominant matrix (slower and more robust convergence) while lower values produce the opposite.
BIH_BNDY_FACTR: specifies the solid wall boundary treatment of artificial dissipation (Active for IFLUX_TYPE=0 only). Second differences at the wall are scaled by BIH_BNDY_FACTR prior to calculating the full biharmonic (4th difference) dissipation terms. The two extreme values correspond to:
IFINE_BNDY_DISSIP: Controls modification of boundary dissipation for schemes other than biharmonic dissipation (IFLUX_TYPE=0) IFINE_BNDY_DISSIP = -1 : Zero out dissipation for tangential boundary condition points (see innerbc_0.f)
BUT this OPTION requires nsmoo_limit(LIM_GEOM) = 0.
DISCRETIZATION TYPE (VISCOUS TERMS)
FNSFACTT: Controls Turbulence model dissipation discretization.
FNSGRAD: Gradient construction options for Navier-Stokes Terms (only active when FNSFACTR = 1.0)
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DISCRETIZATION TYPE (TURBULENCE MODEL)
FNSFACTT: Controls Turbulence model dissipation discretization.
EFACTRC1: Value of entropy fix for COARSE GRID (in multigrid) Discretization Limit value of minimum eigenvalue by EFACTRC1 of maximum eigenvalue.
EFACTRC2: Value of entropy fix for COARSE GRID (in multigrid) Jacobian Limit value of minimum eigenvalue by EFACTRC2 of maximum eigenvalue.
EFACTRF1: Value of entropy fix for FINE GRID Discretization Limit value of minimum eigenvalue by EFACTRF1 of maximum eigenvalue.
EFACTRF2: Value of entropy fix for FINE GRID Jacobian Limit value of minimum eigenvalue by EFACTRF2 of maximum eigenvalue.
ILINE_SOLVE: Select / Omit Line Solver. Line solver increases convergence for Navier-Stokes flows. Robustness problems have been encountered for IFLUX_TYPE=1,2. For IFLUX_TYPE= 0, line solver should always be used.
TIME STEP LIMITING FOR ROBUSTNESS
IMESSAGE_LEVEL: Select Level of output messages when time-step limiting or other limiting occurs.
ISAFE_LEVEL: Controls level of checking for unphysical states in time stepping procedure.
Recommended Value: ISAFE_LEVEL = 2
FACTR_MG: Can be used to enhance robustness of multigrid by decreasing size of transfered residuals to coarse grids. And in turn increasing corrections back to fine grid. Overall convergence history should be identical, but non-linear instabilities on coarse grids may be avoided.
NOTE: FACTR_MG=1 recommended. Other values seldom used.
IGEOM_LIMIT: Option to use (1) or Discard (0) Grid Based Limiting
FGEOM_FRAC: Sets Maximum fraction of limit grid points. When limiting based on grid cell geometry is established (prior to flow calculations), if more than FGEOM_FRAC * nnode grid points are found to be limited (nnode = total number of grid points), execution is halted.
PMIN: Minimum pressure value before limiting occurs. (0.0 < 1.0)
PMIN_MG: Minimum pressure value for omitting multigrid updates (0.0 < 1.0)
RHOMIN: Minimum density value before limiting occurs. (0.0 < 1.0)
RHOMIN_MG: Minimum densuty value for omitting multigrid updates. (0.0 < 1.0)
LOW MACH NUMBER PRECONDITIONING
IPC_LOW_MACH: Select or Omit Low Mach Number Preconditioning
IPC_RAMP: Ability to Ramp in the Low_Mach number preconditioning for increased robustness. (0 < NCYC)
BETA_MIN: relates exclusively to low Mach number preconditioning.
This is an optional parameter and is only active for IPC_LOW_MACH = -1 In this case, BETA_MIN may take on values between 0 and 1. Generally (i.e. IPC_LOW_MACH = +1) low Mach number preconditioning uses the value BETA_MIN = min(1,3 x Mach**2) by default. Lower values of BETA_MIN may be less stable while providing more low Mach number preconditioning effect. Higher numbers produce the opposite, with the effect of low-Mach number preconditioning vanishes for BETA_MIN=1.
INPUT/OUTPUT CONTROL PARAMETERS
IN_PARALLEL: Enable/Disable Parallel Input for Reading Grid Files. Parallel input is implemented as all processors simultaneously reading from a common file system. On some systems, this causes the (Network File System) NFS to overload. To avoid this, IN_PARALLEL=0 instructs each processor to read from the common file system in sequence, one at a time, while the other processors wait their turn. This is slower but more robust for many NFS systems.
IOUT_PARALLEL: Enable/Disable Parallel Output for Writing out Restart Files. Parallel output is implemented as all processors simultaneously writing to a common file system. On some systems, this causes the (Network File System) NFS to overload. To avoid this, IOUT_PARALLEL=0 instructs each processor to write to the common file system in sequence, one at a time, while the other processors wait their turn. This is slower but more robust for many NFS systems.
RESTART FILE AND CHECKPOINT FILE PARAMETERS
INRES_PARALLEL: Enable/Disable Parallel Input for Reading Restart Files. Parallel input is implemented as all processors simultaneously reading from a common file system. On some systems, this causes the (Network File System) NFS to overload. To avoid this, INRES_PARALLEL=0 instructs each processor to read from the common file system in sequence, one at a time, while the other processors wait their turn. This is slower but more robust for many NFS systems.
IRESTART_AUX_TYPE: Determines content of restart.aux.out auxiliary restart file (or directory with partitioned data)
ICHK_PARALLEL: Enable/Disable Parallel output for Checkpoint Files Checkpoint files are written at regular intervals. Parallel output is implemented as all processors simultaneously writing to a common file system. On some systems, this causes the Network File System (NFS) to overload. To avoid this, ICHK_PARALLEL=0 instructs each processor to write to the common file system in sequence, one at a time, while the other processors wait their turn. This is slower but more robust for many NFS systems.
NCYC_CHECKPT: Write out checkpoint file aftyer NCYC_CHECKPT cycles. Alternate checkpt files are written out: checkpt.1 every odd multiple of NCYC_CHECKPT and checkpt.2 every even multiple of NCYC_CHECKPT. Rather than overwriting the latest checkpt file, this approach avoids possible loss of latest checkpt file if failure occurs during checkpt write.
IBL SPECIFIC PARAMETERS (ACTIVE ONLY WHEN RUNNING INTERACTIVE BOUNDARY LAYER)