flowVelocity and drag coefficient issue in the motorBike tutorial

jan90300 · April 11, 2021, 22:13

Hi Everyone,

I am using OpenFOAM 8 and runs the motorBike tutorial.

in the original setting, flowVelocity (20 0 0); I got Cd = 0.35

then I changed the flowVelocity in the document which in 0/include/initialConditions

flowVelocity (20 0 0); ----> "flowVelocity (56 0 0); "
I got Cd=2.71

It's so strange. While the bike speeds up to 56 m/s the Cd should be similar to 0.35

Did I get anything wrong or miss something?

Many thanks.

tomf · April 13, 2021, 04:33

Hi,

I will give you two hints:

$\left(\frac{20}{56}\right)^{2}*2.71=0.346$

check the file system/forceCoeffs for the magUInf you use.

Cheers,
Tom

jan90300 · April 13, 2021, 04:43

Oh.. I'll note this and check further!

Thank you so much, Tom.

Regards,
Han

jan90300 · April 28, 2021, 01:22

I found it. Go to "system" folder, open "forceCoeffs", change the number of "magUInf", it should be as same as "flowVelocity" in the doc "initialConditions"

April 11, 2021, 22:13	flowVelocity and drag coefficient issue in the motorBike tutorial	#1
jan90300 New Member Jan Join Date: Feb 2021 Posts: 6 Rep Power: 6	Hi Everyone, I am using OpenFOAM 8 and runs the motorBike tutorial. in the original setting, flowVelocity (20 0 0); I got Cd = 0.35 then I changed the flowVelocity in the document which in 0/include/initialConditions flowVelocity (20 0 0); ----> "flowVelocity (56 0 0); " I got Cd=2.71 It's so strange. While the bike speeds up to 56 m/s the Cd should be similar to 0.35 Did I get anything wrong or miss something? Many thanks. Last edited by jan90300; April 12, 2021 at 06:19.

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April 13, 2021, 04:33		#2
tomf Senior Member Tom Fahner Join Date: Mar 2009 Location: Breda, Netherlands Posts: 656 Rep Power: 33	Hi, I will give you two hints: $\left(\frac{20}{56}\right)^{2}*2.71=0.346$ check the file system/forceCoeffs for the magUInf you use. Cheers, Tom

April 13, 2021, 04:43		#3
jan90300 New Member Jan Join Date: Feb 2021 Posts: 6 Rep Power: 6	Oh.. I'll note this and check further! Thank you so much, Tom. Regards, Han

April 28, 2021, 01:22		#4
jan90300 New Member Jan Join Date: Feb 2021 Posts: 6 Rep Power: 6	I found it. Go to "system" folder, open "forceCoeffs", change the number of "magUInf", it should be as same as "flowVelocity" in the doc "initialConditions"