temperture limited

alikami · June 9, 2010, 01:13

in my flow case (nozzle)
fluent says temperature limited to 1500 k in zone 2
zone 2 is fluid
why is this error ...
cells with this tempearture are at start of convergent portion of nozzle
nozzle is operating under overexpanded condition
plz help

tejinder · June 14, 2010, 00:00

hello
m facing the same problem with my model.. initially i used air as fluid passing through my model and it gave me convergence but when i changed my fluid from air to nitrogen or helium its started giving me message temperature limited to some number of cells in zone 2 which is fluid zone. if u could tell me the cause of problem i'll be very thankful to u..

alikami · June 14, 2010, 07:06

This kind of problem may happen in large gradient areas.
check the gradient adoption in fluent manual chapter 26
Regards
Ali

enigma · July 10, 2010, 00:59

One can easily get rid of this problem, by increasing the temperature limit in
- Solution Controls: Limits:

In any adiabatic flowfield, the total temperature is conserved, even if the flow goes through shock waves - total temperature is constant. In a nozzle simulation, the best boundary condition at the throat would be a pressure inlet, where the user sets the TOTAL TEMPERATURE. In one of my simulations, this is 2400K. Theoretically, the temperature limit can now be set to 2401K, and no one cell should ever have a temperature in the excess of 2400K and hence the "temperature limit" warning should not appear. However, this is only a theoretical case with an infinitely fine grid. In my simulation, I have set the temperature limit to 3000K, 600K above the total temperature, and I STILL get this error message. This is a sign that in the region where this happens, the mesh is not nearly "fine enough" yet.

Although I can get rid of this error message by refining the mesh in those areas, I'm not sure whether or not setting that temperature limit has any influence on convergence - hence, for convergence reasons, is it better to set this temperature limit to very high values (so that the error message wouldn't appear) or set it to quite low values (in the range of the total temperature)??

Thanks for your input!

June 9, 2010, 01:13	temperture limited	#1
alikami Member ali Join Date: May 2009 Posts: 58 Rep Power: 16	in my flow case (nozzle) fluent says temperature limited to 1500 k in zone 2 zone 2 is fluid why is this error ... cells with this tempearture are at start of convergent portion of nozzle nozzle is operating under overexpanded condition plz help

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June 14, 2010, 00:00		#2
tejinder New Member Tejinder pal singh Join Date: May 2010 Posts: 1 Rep Power: 0	hello m facing the same problem with my model.. initially i used air as fluid passing through my model and it gave me convergence but when i changed my fluid from air to nitrogen or helium its started giving me message temperature limited to some number of cells in zone 2 which is fluid zone. if u could tell me the cause of problem i'll be very thankful to u..

June 14, 2010, 07:06		#3
alikami Member ali Join Date: May 2009 Posts: 58 Rep Power: 16	This kind of problem may happen in large gradient areas. check the gradient adoption in fluent manual chapter 26 Regards Ali

July 10, 2010, 00:59		#4
enigma New Member Join Date: Mar 2009 Posts: 21 Rep Power: 17	One can easily get rid of this problem, by increasing the temperature limit in - Solution Controls: Limits: In any adiabatic flowfield, the total temperature is conserved, even if the flow goes through shock waves - total temperature is constant. In a nozzle simulation, the best boundary condition at the throat would be a pressure inlet, where the user sets the TOTAL TEMPERATURE. In one of my simulations, this is 2400K. Theoretically, the temperature limit can now be set to 2401K, and no one cell should ever have a temperature in the excess of 2400K and hence the "temperature limit" warning should not appear. However, this is only a theoretical case with an infinitely fine grid. In my simulation, I have set the temperature limit to 3000K, 600K above the total temperature, and I STILL get this error message. This is a sign that in the region where this happens, the mesh is not nearly "fine enough" yet. Although I can get rid of this error message by refining the mesh in those areas, I'm not sure whether or not setting that temperature limit has any influence on convergence - hence, for convergence reasons, is it better to set this temperature limit to very high values (so that the error message wouldn't appear) or set it to quite low values (in the range of the total temperature)?? Thanks for your input!