Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam Assignment for the course CFD with OpenSource Software OF21x Ardalan Javadi Applied Mechanics/Fluid Dynamics, Chalmers University of Technology, Gothenburg, Sweden 2012-09-09 Ardalan Javadi Assignment 1 2012-09-09 1 / 15
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Assignment for the course CFD with OpenSource …hani/kurser/OS_CFD_2012/assignment1/...Assignment for the course CFD with OpenSource Software OF21x Ardalan Javadi Applied Mechanics/Fluid
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The same geometry is simulated using finer cells. The flow structure islarge enough to be captured with previous coarse mesh.The results of twomeshes are very similar. The only visible difference would be the two small
vortices nested at the two bottom corners of the cavity.
A bulk of liquid is freed on left corner of the domain at time zero and dueto the gravity, splashes over the bottom of the domain. The process issimulated for first 1 second. The two-phase flow is captured at three
A flow over backward-facing step is studied which separates at step edge andreattachs about 5H downstream of the step, H is step height. The reattachmentpoint is emphesised by a line. The turbulence is developing with spreading shearlayer that strarts at separation point and extends over recirculation region. The ε
shows the development of shear layer. Q-criterion (see next slide) shows thestructure of the flow. The separation makes turbulence with the length scale ofthe step height. This worth mentioning that there is a large vortex above the
separation point, near the top wall. The pressure fluctuations of the separation atthe step edge might cause this vortex.
Q is a proper orthogonal tensor, For a three-dimensional smooth velocityfield v(x, t), available Galilean-invariant vortex criteria use the velocitygradient decomposition:
∇v = S + Ω
where S = 12
[∇v + (∇v)T
]is the rate-of-strain tensor, and
Ω = 12
[∇v − (∇v)T
]is the vorticity tensor. Historically, the first
three-dimensional vortex criterion using above equation called Q-criterionwhich defines a vortex as a spatial region where:
Duct Flow over Roughness with higher Reynolds Number and Finer Grid
Fine Mesh
Streamwise velocity
Pressure
Vorticity
Turbulent Kinetic Energy
The twice finer grid in each direction is used to assess the grid effectiveness in ourcomputations. The initial condition is mapped from the coarse grid. The Reynolds number at
inflow based on the roughness hieght is 2000.Ardalan Javadi Assignment 1 2012-09-09 14 / 15
The flow in the duct is using pisoFoam solver with two meshes and twoReynolds numbers. A new blockMesh file is prepared and the geometry isblocked and meshed using what is learnt in first week. Owing to lenght
scale of the flow (roughness hieght) the results of two meshes are different.The roughness make the flow more turbulent as expected, the structures
around fourth and fifth roughness is very similar.