Very slow convergence for transient flow

Akanksha90 · January 29, 2018, 10:43

Hello,
I am doing CHT simulations with transient solver for an electric motor. I have noticed that the heat transfer stability and temperature plots are progressing very slow even thought the time step is only 0.01 seconds.
Any tips to improve the solving time?
Thank you

fluid23 · January 29, 2018, 12:14

Try adjusting your relaxation factors on your solver(s).

ashokac7 · January 30, 2018, 01:51

Quote:

Originally Posted by Akanksha90

Hello,
I am doing CHT simulations with transient solver for an electric motor. I have noticed that the heat transfer stability and temperature plots are progressing very slow even thought the time step is only 0.01 seconds.
Any tips to improve the solving time?
Thank you

If I am correct for few thousand RPM time step of 0.01 s is not very small. In my simulations with gear box or pump I have used 1e-5 sec as my time step still one of my senior thinks that it is large. So the criteria for setting up your time step may be such that you have 1 degree revolution per time step. This may be the reason for slow convergence. But if you are not simulating the case with the revolution of the motor then your time step may be correct.

me3840 · February 7, 2018, 20:42

Do you mean the temperature of the solids? Solids taking a long time to respond to temperature is pretty normal. Have you looked at the time constant for your solids? A hand calculation will get you pretty close to telling you how long it will take for them to stabilize.

January 29, 2018, 10:43	Very slow convergence for transient flow	#1
Akanksha90 New Member Akanksha Rawat Join Date: Apr 2014 Posts: 29 Rep Power: 12	Hello, I am doing CHT simulations with transient solver for an electric motor. I have noticed that the heat transfer stability and temperature plots are progressing very slow even thought the time step is only 0.01 seconds. Any tips to improve the solving time? Thank you

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January 29, 2018, 12:14		#2
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 18	Try adjusting your relaxation factors on your solver(s).

February 7, 2018, 20:42		#4
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 25	Do you mean the temperature of the solids? Solids taking a long time to respond to temperature is pretty normal. Have you looked at the time constant for your solids? A hand calculation will get you pretty close to telling you how long it will take for them to stabilize.