Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
Assignment for the courseCFD 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
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
cavity
Mesh, Velocity field and Streamlines
Mesh andVelocity field
Streamlines coloredby velocity mag.
The flow over a cavity with 1 m/s velocity at the top is laminarlysimulated. The velocity is not too high, so the flow structure inside the
cavity is symmetric.
Ardalan Javadi Assignment 1 2012-09-09 2 / 15
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
cavityFine
Mesh, Velocity field and Streamlines
Mesh andVelocity field
Streamlines coloredby velocity mag.
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.
Ardalan Javadi Assignment 1 2012-09-09 3 / 15
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
cavityHighRe
Mesh, Velocity field and Streamlines
Mesh andVelocity field
Streamlines coloredby velocity mag.
The same geometry is simulated by decreasing the kinematic viscosity by afactor of 10. The flow structure inside of the cavity is not symmetric
anymore.Ardalan Javadi Assignment 1 2012-09-09 4 / 15
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
cavityGrade
Mesh, Velocity field and Streamlines
Mesh andVelocity field
Streamlines coloredby velocity mag.
Regarding the basic point which the structures near the walls are smaller,the cells in the near wall regions are got smaller.
Ardalan Javadi Assignment 1 2012-09-09 5 / 15
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
cavityClipped
Mesh, Velocity field and Streamlines
Mesh andVelocity field
Streamlines coloredby velocity mag.
An asymmetric cavity is simulated using the coarse mesh and the sameboundary conditions. The primary vortex is a little pushed up and two
large secondary vortices are nested at the two bottom corners of the cavity.
Ardalan Javadi Assignment 1 2012-09-09 6 / 15
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
damBreak
A Two-Phase Flow For 1 Sec.
Mesh and Phases att=0s
Mesh and Phases att=0.35s
Mesh and Phases att=1s
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
moments.
Ardalan Javadi Assignment 1 2012-09-09 7 / 15
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
damBreakFine
A Two-Phase Flow For 1 Sec. with Fine Mesh
Mesh and Phases att=0s
Mesh and Phases att=0.35s
Mesh and Phases att=1s
The same geometry is simulated using fine grid. Due to directcamparioson of two grids, the computation of fine grid is conducted to 1
second. The splash process makes the flow structures small, so thedifference between two grids are ostensible.
Ardalan Javadi Assignment 1 2012-09-09 8 / 15
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
pitzDaily
Flow over Backward-Facing Step
Mesh
Turbulent Kinetic Energy
Streamlines coloredby Velocity Mag.
Streamwise Velocity
Q-Criterion
Ardalan Javadi Assignment 1 2012-09-09 9 / 15
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
pitzDaily
ε, close up at step edge
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.
Ardalan Javadi Assignment 1 2012-09-09 10 / 15
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
pitzDaily
Q-Criterion
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:
Q = 12
[|Ω|2 − |S|2
]Ardalan Javadi Assignment 1 2012-09-09 11 / 15
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
ductFlow
Duct Flow over Roughness
The computationaldomain, h=0.1mm
Coarse Mesh Turbulent Kinetic Energy
Streamwise velocity Pressure Vorticity
A turbulent flow in a duct with rough bottom wall is simulated with k-εturbulece model. The Reynolds number at inflow based on the roughness
hieght is 1000. The flow is water with ν = 10−5.
Ardalan Javadi Assignment 1 2012-09-09 12 / 15
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
ductFlowHighRe
Duct Flow over Roughness with higher Reynolds Number
Streamwise velocity
Pressure
Vorticity
Turbulent Kinetic Energy
The Reynolds number at inflow based on the roughness hieght is 2000.
Ardalan Javadi Assignment 1 2012-09-09 13 / 15
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
ductFlowHighReFine
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
Solver: icoFoam Solver: interFoam/laminar Solver: simpleFoam Solver: pisoFoam
ductFlowHighReFine
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.
Ardalan Javadi Assignment 1 2012-09-09 15 / 15
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