Combustion and high Mach number problem

Whitebear · June 10, 2015, 23:32

During circulating fluidized bed combustion calculation, I see Notice message: The maximum Mach number is 1.651E+01 and the number is going higher. According to design of furnace guidebook, the maximum speed of flue gas is below 25m/s. What is the cause of the problem? I need your help.

Opaque · June 11, 2015, 08:12

The iterative process is very likely having convergence problems in some region of the model.

I suggest to activate the "Output Residuals" for a backup file, run the case, write a backup file and post-process the residuals for the equations. Look for the location of the maximum residual for the equation of interest, and review mesh quality, flow conditions, anything that may hint what the source of the problem might be.

ghorrocks · June 11, 2015, 18:49

As opaque says, your simulation is diverging. It has not crashed out yet but it will soon.

This is the FAQ on it: http://www.cfd-online.com/Wiki/Ansys...do_about_it.3F

Whitebear · June 11, 2015, 20:11

Thank you very much indeed. I'll try as you say.

June 10, 2015, 23:32	Combustion and high Mach number problem	#1
Whitebear Member Jinwhan Ryuk Join Date: Feb 2013 Location: South Korea Posts: 91 Rep Power: 13	During circulating fluidized bed combustion calculation, I see Notice message: The maximum Mach number is 1.651E+01 and the number is going higher. According to design of furnace guidebook, the maximum speed of flue gas is below 25m/s. What is the cause of the problem? I need your help.

June 11, 2015, 08:12		#2
Opaque Senior Member Join Date: Jun 2009 Posts: 1,800 Rep Power: 32	The iterative process is very likely having convergence problems in some region of the model. I suggest to activate the "Output Residuals" for a backup file, run the case, write a backup file and post-process the residuals for the equations. Look for the location of the maximum residual for the equation of interest, and review mesh quality, flow conditions, anything that may hint what the source of the problem might be. dotapro likes this.

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June 11, 2015, 18:49		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,697 Rep Power: 143	As opaque says, your simulation is diverging. It has not crashed out yet but it will soon. This is the FAQ on it: http://www.cfd-online.com/Wiki/Ansys...do_about_it.3F

June 11, 2015, 20:11		#4
Whitebear Member Jinwhan Ryuk Join Date: Feb 2013 Location: South Korea Posts: 91 Rep Power: 13	Thank you very much indeed. I'll try as you say.