compressible flow simulation

hnemati · April 16, 2019, 10:38

Dear all
I am currently trying to simulate the combustion of methane-air in an incinerator, where methane is injected through a nozzle and mixed with air. I used to apply low-Mach number approximation for the simulation since the maximum Mach number was around 0.3. I recently got a case that the Mach number is around 2 at the nozzle. However, the rest of the flow is at Mach <0.3. The question is, the low-Mach number is still valid or I have use fully compressible equations.
Thank you

LuckyTran · April 16, 2019, 15:49

What software are you using and what equations are being solved?

For non-reacting flows, most commercial CFD software (Fluent, Star-CCM, CFX, mostFOAM) solve the compressible navier-stokes and there is no problem.

For reacting flows it's a little more complicated because of the combustion model usually has limitations.

FMDenaro · April 16, 2019, 16:02

Quote:

Originally Posted by hnemati

Dear all
I am currently trying to simulate the combustion of methane-air in an incinerator, where methane is injected through a nozzle and mixed with air. I used to apply low-Mach number approximation for the simulation since the maximum Mach number was around 0.3. I recently got a case that the Mach number is around 2 at the nozzle. However, the rest of the flow is at Mach <0.3. The question is, the low-Mach number is still valid or I have use fully compressible equations.
Thank you

Yes, you must use the compressible flow formulation

hnemati · April 17, 2019, 03:09

Thank you for your reply. I use fluent and the reacting flow equations are solved.

Quote:

Originally Posted by LuckyTran

What software are you using and what equations are being solved?

For non-reacting flows, most commercial CFD software (Fluent, Star-CCM, CFX, mostFOAM) solve the compressible navier-stokes and there is no problem.

For reacting flows it's a little more complicated because of the combustion model usually has limitations.

LuckyTran · April 17, 2019, 10:59

Fluent always solves compressible navier-stokes (unless you are using the inviscid flow model). If you use detailed chemistry there is also no issue.

Some of the combustion models have limitations on compressibility effects due to the nature of the models themselves. Since you're unwilling to tell us what model you are using, I'll leave it up to you to figure it out.

April 16, 2019, 10:38	compressible flow simulation	#1
hnemati Member SAM Join Date: Apr 2012 Posts: 74 Rep Power: 14	Dear all I am currently trying to simulate the combustion of methane-air in an incinerator, where methane is injected through a nozzle and mixed with air. I used to apply low-Mach number approximation for the simulation since the maximum Mach number was around 0.3. I recently got a case that the Mach number is around 2 at the nozzle. However, the rest of the flow is at Mach <0.3. The question is, the low-Mach number is still valid or I have use fully compressible equations. Thank you

April 16, 2019, 15:49		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	What software are you using and what equations are being solved? For non-reacting flows, most commercial CFD software (Fluent, Star-CCM, CFX, mostFOAM) solve the compressible navier-stokes and there is no problem. For reacting flows it's a little more complicated because of the combustion model usually has limitations. hnemati likes this.

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April 17, 2019, 10:59		#5
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	Fluent always solves compressible navier-stokes (unless you are using the inviscid flow model). If you use detailed chemistry there is also no issue. Some of the combustion models have limitations on compressibility effects due to the nature of the models themselves. Since you're unwilling to tell us what model you are using, I'll leave it up to you to figure it out.