Advice for wind problem?

griztown · November 3, 2009, 11:20

Hi,

I'm trying to run OpenFOAM to get the lift and drag on an object that is just above the ground in 50mph winds. Looking at the different solvers, I thought using icoFoam to start might be a good idea, followed by simpleFoam if I want to include turbulence. Does that make sense? Currently running icoFoam, my courant number starts out around 0.05 but then quickly explodes and I get a floating point exception.

Any advice is greatly appreciated!
Thanks

franzisko · November 3, 2009, 12:00

Hi,

as far as i know (maybe I am not so skilled...)

in principle your strategy is good but...icoFoam is a transient solver while simpleFoam is a stationary solver. for realistic case a transient simulation is not possible without turbulence modeling because the involved Reynolds number are too large. hence your simulations tend to explode after a while beacuse you can't capture the dynamics. even if your starting courant number is low. if you want to use icoFoam you have to lower Reynolds number (e.g., increasing viscosity or...). concluding I would suggest to use simpleFoam with different turbulence models and, if you want, to try a LES simulation, always checking the aerodynamical coefficients

bye, Francesco

griztown · November 3, 2009, 13:58

Thanks Francesco! Going with simpleFoam definitely worked. Now for some post processing.

griztown · November 3, 2009, 18:43

I'm trying to calculate the forces on my object using the forces function in the controlDict file. The number seem a bit off so I'm curious how some of my assumptions may be affecting the problem. For example, I've used an absolute pressure of zero since this is an incompressible problem. I'm pretty sure this is okay, but thought I should check.

Also, what units are the forces output in? I'm assuming Newtons, is that correct?

Thanks!

November 3, 2009, 11:20	Advice for wind problem?	#1
griztown New Member Ted Brenner Join Date: Oct 2009 Location: Oregon, WI Posts: 12 Rep Power: 17	Hi, I'm trying to run OpenFOAM to get the lift and drag on an object that is just above the ground in 50mph winds. Looking at the different solvers, I thought using icoFoam to start might be a good idea, followed by simpleFoam if I want to include turbulence. Does that make sense? Currently running icoFoam, my courant number starts out around 0.05 but then quickly explodes and I get a floating point exception. Any advice is greatly appreciated! Thanks

November 3, 2009, 12:00	wind turbine	#2
franzisko New Member Francesco Join Date: Jul 2009 Posts: 13 Rep Power: 17	Hi, as far as i know (maybe I am not so skilled...) in principle your strategy is good but...icoFoam is a transient solver while simpleFoam is a stationary solver. for realistic case a transient simulation is not possible without turbulence modeling because the involved Reynolds number are too large. hence your simulations tend to explode after a while beacuse you can't capture the dynamics. even if your starting courant number is low. if you want to use icoFoam you have to lower Reynolds number (e.g., increasing viscosity or...). concluding I would suggest to use simpleFoam with different turbulence models and, if you want, to try a LES simulation, always checking the aerodynamical coefficients bye, Francesco

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November 3, 2009, 13:58		#3
griztown New Member Ted Brenner Join Date: Oct 2009 Location: Oregon, WI Posts: 12 Rep Power: 17	Thanks Francesco! Going with simpleFoam definitely worked. Now for some post processing.

November 3, 2009, 18:43		#4
griztown New Member Ted Brenner Join Date: Oct 2009 Location: Oregon, WI Posts: 12 Rep Power: 17	I'm trying to calculate the forces on my object using the forces function in the controlDict file. The number seem a bit off so I'm curious how some of my assumptions may be affecting the problem. For example, I've used an absolute pressure of zero since this is an incompressible problem. I'm pretty sure this is okay, but thought I should check. Also, what units are the forces output in? I'm assuming Newtons, is that correct? Thanks!