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March 19, 2014, 15:44 |
Weird Cl for a car
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#1 |
Member
Michele
Join Date: Dec 2013
Posts: 32
Rep Power: 12 |
I'm simulating a classical flow around a car...i have included obviously a moving street and rotating wheels.
The simulation is steady with a k-e model. I have done the setup for the reports for Cd and Cl. The Cd is normal...but the Cl of the car is crazy!...the Cl is around 27 watching the details of the report a huge contribution for the Cl is coming from the wheels...what is happening?? Thanks. |
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March 20, 2014, 08:24 |
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#2 |
Member
Join Date: Jul 2013
Posts: 55
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It is normal for rotating cylinder to provide a force that is perpendicular to the flow which is a lift.
Here's a wiki on that. Maybe your results are valid. (Maybe they are not) You could check the magnitude of the lift force (not lift coefficient) and compare it to gravity force. Rotation of the wheels is not something that can overcome gravity... There should be several order of magnitude of difference. EDIT : also, remove the rotation from the wheel and run your simulation once. It should be near 0. |
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March 20, 2014, 09:31 |
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#3 |
Senior Member
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Location: USA
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Is your simulation converged? Did you set up the reference values correctly?
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March 21, 2014, 04:28 |
bho
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#4 |
Member
Michele
Join Date: Dec 2013
Posts: 32
Rep Power: 12 |
Taking the Magnus effect into the game the Cl is still non-physical.\
The solution converged and the reference values are the same of the Cd report wich is ok. I`m feeling like i`m missing something in the setup...i do not know I have run the sim with some different freestream speed: |
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March 21, 2014, 04:34 |
Report
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#5 |
Member
Michele
Join Date: Dec 2013
Posts: 32
Rep Power: 12 |
this is the full report:
as you can see the contribution for the weird Cl fully comes from the wheels: |
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March 21, 2014, 17:28 |
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#6 |
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Location: USA
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Can you plot pressure on the surface of the wheels? What does it look like? Do the values make sense?
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March 22, 2014, 09:03 |
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#7 |
Senior Member
Anonymous
Join Date: Dec 2011
Location: USA
Posts: 108
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What do you have your reference pressure at in setting up the coefficient of lift? Changing this value will drastically change your coefficient value
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March 22, 2014, 15:13 |
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#8 | |
Member
Michele
Join Date: Dec 2013
Posts: 32
Rep Power: 12 |
Quote:
Anyway...this is the pressure on the wheels...does not look weird? |
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March 22, 2014, 15:50 |
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#9 | |
Senior Member
Anonymous
Join Date: Dec 2011
Location: USA
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Quote:
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March 22, 2014, 18:54 |
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#10 |
Senior Member
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Location: USA
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Those pressures look fine. Are you sure you have the reference values set correctly? I don't think you do. What's the physical value of the lift force?
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March 23, 2014, 15:17 |
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#11 |
Member
Michele
Join Date: Dec 2013
Posts: 32
Rep Power: 12 |
Yeah, you were right. I have set up the reference pressure to 0Pa and now the Cl is back to normality!
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March 23, 2014, 15:41 |
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#12 |
Senior Member
Anonymous
Join Date: Dec 2011
Location: USA
Posts: 108
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Good to hear!
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