# Basics : Backward facing step — Welcome to LS-DYNA Examples

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The 2D laminar backward facing step is a widely encountered benchmark for CFD code testing. The present example features a mesh size of 0.05 and a Reynolds number of 800. The second order steady state solver is used, requires LS-DYNA MPP Dev 114223 (or higher) with double precision.

## Animated Result

Fluid velocity fringes

## Keywords

```*KEYWORD
*TITLE
*DATABASE_BINARY_D3PLOT
*DEFINE_CURVE_TITLE
*ICFD_BOUNDARY_NONSLIP
*ICFD_BOUNDARY_PRESCRIBED_VEL
*ICFD_BOUNDARY_PRESCRIBED_PRE
*ICFD_CONTROL_GENERAL
*ICFD_CONTROL_OUTPUT
*ICFD_MAT
*ICFD_PART
*ICFD_PART_VOL
*ICFD_SECTION
*INCLUDE
*MESH_SURFACE_ELEMENT
*MESH_SURFACE_NODE
*MESH_VOLUME
*PARAMETER
*END
```

## Reduced Input

```\$-----------------------------------------------------------------------------
\$
\$ Example provided by Iñaki (LSTC)
\$
\$ E-Mail: info@dynamore.de
\$ Web: http://www.dynamore.de
\$
\$ Copying for non-commercial usage allowed if
\$ copy bears this notice completely.
\$
\$X------------------------------------------------------------------------------
\$X
\$X 1. Run file as is.
\$X    Requires LS-DYNA MPP Dev 114223 (or higher) with double precision
\$X
\$X------------------------------------------------------------------------------
\$# UNITS: Dimensionless
\$X------------------------------------------------------------------------------
\$X
*KEYWORD
*TITLE
ICFD Laminar Backward facing step
*INCLUDE
mesh.k
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
\$                                                                              \$
\$                             PARAMETERS                                       \$
\$                                                                              \$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
*PARAMETER
I   It_max     10000
R  dt_plot       200
\$
\$--- Fluid
\$
Rrho_fluid         1
R mu_fluid 1.6665e-3
Rvel_fluid         1
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
\$                                                                              \$
\$                           ICFD CONTROL CARDS                                 \$
\$                                                                              \$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
*ICFD_CONTROL_GENERAL
1         0         0
&It_max      1e-8      1e-8                   1         1         1         0
*ICFD_CONTROL_OUTPUT
\$#    msgl
3
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
\$                                                                              \$
\$                       ICFD PARTS/ SECTION/ MATERIAL                          \$
\$                                                                              \$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
*ICFD_MAT
\$#     mid       flg        ro       vis
1         1&rho_fluid &mu_fluid
*ICFD_PART
\$#     pid     secid       mid
1         1         1
*ICFD_PART
\$#     pid     secid       mid
2         1         1
*ICFD_PART
\$#     pid     secid       mid
3         1         1
*ICFD_PART_VOL
\$#     pid     secid       mid
10         1         1
\$#   spid1     spid2     spid3
1         2         3
*ICFD_SECTION
\$#     sid
1
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
\$                                                                              \$
\$                                                                              \$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
*ICFD_BOUNDARY_NONSLIP
\$#     pid
3
*ICFD_BOUNDARY_PRESCRIBED_VEL
\$#     pid       dof       vad      lcid        sf       vid     death     birth
1         1         1         1  1.000000         01.0000E+28     0.000
*ICFD_BOUNDARY_PRESCRIBED_VEL
\$#     pid       dof       vad      lcid        sf       vid     death     birth
1         2         1         2  1.000000         01.0000E+28     0.000
*ICFD_BOUNDARY_PRESCRIBED_PRE
\$#     pid       dof       vad      lcid        sf       vid     death     birth
2         1         1         2  1.000000         01.0000E+28     0.000
*DEFINE_CURVE_TITLE
Vel Inlet
\$#    lcid      sidr       sfa       sfo      offa      offo    dattyp
1                    &vel_fluid
\$#                a1                  o1
0.0                 1.0
10000.0                 1.0
*DEFINE_CURVE
\$#    lcid      sidr       sfa       sfo      offa      offo    dattyp
2
\$#                a1                  o1
0.0                 0.0
10000.0                 0.0
*ICFD_INITIAL
\$#     pid
0         1
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
\$                                                                              \$
\$                            ICFD MESH KEYWORDS                                \$
\$                                                                              \$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
*MESH_VOLUME
\$#   volid
10
\$#    pid1      pid2      pid3
1         2         3
*MESH_BL
\$#     pid
3         1
*MESH_BL_SYM
\$#     pid
1
*MESH_BL_SYM
\$#     pid
2
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
\$                                                                              \$
\$                             DATABASE (OUTPUT)                                \$
\$                                                                              \$
\$---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8
*DATABASE_BINARY_D3PLOT
&dt_plot
*END
```

## Description

The 2D laminar backward facing step is a widely encountered benchmark for CFD code testing. The present example features a mesh size of 0.05 and a Reynolds number of 800. The second order steady state solver is used.

References :

[1] B. F. ARMALY, F. DURSTS, J. C. F. PEREIRA  AND B. SCHONUNG , Experimental and theoretical investigation of
backward-facing step flow, Institute of Hydromechanics, Section I11 : Mechanics of Turbulent Flows, University of
Karlsruhe, KaiserstraBe 12, D-7500 Karlsruhe, F.R.G.

[2] EXPERIMENTAL AND NUMERICAL INVESTIGATION
OF 2-D BACKWARD-FACING STEP FLOW. T. LEE AND D. MATEESCU
Department of Mechanical Engineering, McGill University, Montreal, Quebec, Canada

[3] E. Erturk,Numerical solutions of 2-D steady incompressible flow over
a backward-facing step, Part I: High Reynolds number solutions,Gebze Institute of Technology, Energy Systems Engineering Department, Gebze, Kocaeli 41400, Turkey