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PISO's strange behavior at different meshes :(

Posted February 25, 2013 at 07:19 by skeptik (CFD notes)

1. mesh quad+tri+3D extruded. at 17 grad most flow around airfoil is laminar

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2. mesh only tri+3D extruded. at 15 grad flow behind foil is completely turbulent

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so this pictures shows that we cannot get proper results for Cx, Cy due to bad prediction of the flow detachment.

try to find a solution, may be OF 2.1 will show better results
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Bubbly flow boundary conditions

Posted February 20, 2013 at 07:58 by beauty

meeting the same problem
Originally Posted by Vivek
Hey Danny,

It is very simple but not straight forward. In many cases you would seen people model the top gas-liquid surface as outlet using two-fluid model. But, I hope that you would agree with me that two-fluid model is not expected to predict the gas-liquid surface. Ypu can model the top gas-liquid interface as follows:

1. Set top surface as inlet. Set all componet of liquid velocity to zero. Set vertical gas velocity to terminal rise
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Good news about airfoil and OpenFoam

Posted February 20, 2013 at 03:42 by skeptik (CFD notes)

So, at the end of the testing OpenFOAM/simpleFoam, i get:

U=21.3, Re=0.44e6,

LowRe case, LaunderSharmaKE:
1. OF 1.7 cannot solve the case with kEpsilon on hex+tetra 2D mesh. It just crashes.

2. There are a lots of details when you use LowRe LSkEps model, you need lots of iteration, lots of interpolation data to provide better accuracy.

3. People invented k-omega for different flows near the walls. And better one - kOmega...
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Hey, Dude, be careful with liftDir/dragDir in controlDict

Posted February 19, 2013 at 05:41 by skeptik (CFD notes)

When U is changed due to angle of attack you should change controlDict in libForces section.

So, what can you get when you have proper controlDict

U=56.4, Re=1.6e6

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The mesh was refined so it was OK after checkMesh

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not bad) the next - recalculate LowRe K-eps, just for fun.
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TUI commands for running a Transient simulation in ANSYS FLUENT

Posted February 18, 2013 at 11:22 by diamondx

The TUI command solve/iterate 100 just iterates 100 more iterations. This is used for running steady simulations.

Use the following commands for running a transient simulation:

solve/set/time-step 1e-2 ( for setting the time step size)

solve/dual-time-iterate 100 40 ( 100 is the number of time steps and 40 is the iterations per time steps)
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