The aim of this test case is to validate steadystate flow over a backwardfacing step. The incompressible, turbulent case is validated with the experimental results of Driver and Seegmiller [1] as archived in the NASA Turbulence Modeling Resource [2]. The following parameters have been analysed:
The geometry was meshed locally and a mesh upload to the platform was performed.
Import validation project into workspace
The geometry is constructed based on the reference case [1], as shown in Fig.1. The height of the step is h=12.7
$h=12.7$cm, and the tunnel height is 8h
$8h$. The origin is located at the base of the step. The face details have been given in Table 1.
Face(s)  Type 

A  Inlet 
B+H  Symmetry 
C+D+E+G  Walls 
F  Outlet 
The blockMesh tool was used to generate the mesh locally (see Fig.2. and Table 2.). A singlecell width was assigned in the zdirection to ensure a 2D mesh.
A typical property of the generated mesh is the y+
${y}^{+}$(“yplus”) value, which is defined as the nondimensionalized distance to the wall; it is given by y+=u∗y/ν
${y}^{+}={u}^{\ast}y/\nu $. A y+
${y}^{+}$value of 1 would correspond to the upper limit of the laminar sublayer.
 Explicit resolution of the nearwall region: The first cell lies at most at the boundary of the laminar sublayer and no further. Here, y+
${y}^{+}$
value is 1 or below.
 Use of wallfunctions to resolve the nearwall region: There is no need to place cells very close to the laminar sublayer, and typically 30⩽y+⩽300
$30\u2a7d{y}^{+}\u2a7d300$
.
A y+
${y}^{+}$value of 30 was used for the inflation layer. The k−ω
$k\omega $SST turbulence model was chosen, with wall functions for nearwall treatment of the flow.
Tool Type : OPENFOAM®
Analysis Type : simpleFoam
Mesh and Element types :
Mesh type  Number of volumes  Type 

blockMesh  5.5×105
$5.5\times {10}^{5}$

2D hex 
Fluid:
Kinematic Viscocity (ν
$\nu $): 1.4694×10−5 m2s−1
$1.4694\times {10}^{5}\text{}{m}^{2}{s}^{1}$
The boundary conditions for the simulation are shown in Table 3.
Boundary Conditions:
Parameter  Inlet  Symmetry  Walls  Outlet 

Velocity  44.2 ms−1
$44.2\text{}m{s}^{1}$

Symmetry  0.0 ms−1
$0.0\text{}m{s}^{1}$

Zero Gradient 
Pressure  Zero Gradient  Symmetry  Zero Gradient  0.0
$0.0$
Pa 
k
$k$

5.336 m2s−2
$5.336\text{}{m}^{2}{s}^{2}$

Symmetry  Wall Function  Zero Gradient 
ω
$\omega $

182.399 s−1
$182.399\text{}{s}^{1}$

Symmetry  Wall Function  Zero Gradient 
Velocity Profiles
Shown below in Figure 3 are comparisons of velocity profiles from SimScale simulation results with the reference [1] at different distances into the domain. All distances have been normalized with the step height h
$h$, and the velocity is normalized with respect to the inlet velocity vin=44.2 ms−1
${v}_{in}=44.2\text{}m{s}^{1}$.
Fig.3. Velocity profiles at different depths into the domain.
Coefficient of Pressure
Shown below in Figure 4 is the comparison of the coefficient of pressure Cp=P−P∞12ρV2∞
${C}_{p}=\frac{P{P}_{\mathrm{\infty}}}{\frac{1}{2}\rho {V}_{\mathrm{\infty}}^{2}}$from SimScale simulation results with the reference [1] at the lower and upper walls.
Fig.4. Coefficient of Pressure at lower and upper walls
Reattachment Length
The reattachment length is the distance from the step at which the flow resumes in the positive flow direction all over the crosssection. The reattachment length was calculated to be 6.82 cm
$6.82\text{}cm$, which lies within a 12%
$12\mathrm{\%}$error limit of the experimental value of 7.74 cm
$7.74\text{}cm$[2].
[1]  (1, 2, 3, 4) Driver, D. M. and Seegmiller, H. L., “Features of Reattaching Turbulent Shear Layer in Divergent Channel Flow,” AIAA Journal, Vol. 23, No. 2, Feb 1985, pp. 163171. 
[2]  (1, 2) Langley Research Center: Turbulence Modeling Resource – 2D Backward Facing Step 
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