Operating Density

kr660170 · August 15, 2018, 07:49

Hello Guys,

Can someone explain me clearly what is the use of operating density that is found in the BC-Operating conditions?

LuckyTran · August 15, 2018, 10:55

It's highly dependent on what models you have activated the purpose of the operating density. But presumably, you likely have gravity enabled and are using a Boussinesq model. The operating density would be the unperturbed density. You really should state what models you are using...

kr660170 · August 16, 2018, 03:24

Thanks Lucky for your reply. I have defined density as piecewise-linear and i have enabled gravity Option. I am working on the Simulation of melting process of metal foam with Paraffin wax.

So basically operating density is used when you define the density as boussineseq approximation right?

LuckyTran · August 16, 2018, 11:16

Whenever you enable gravity an operating density is needed. This density is needed due to hydrostatic effects (pressure changes due to elevation) which occur when there is gravity and because Fluent uses gauge pressures for BC's and so on.

If you do use Boussinesq, you don't need the operating density because of the way Boussinesq works (operating temperature is the key parameter here).

If you do not use Boussinesq, then operating density is needed. Fluent automatically takes an average pressure and uses it as the operating density unless you click the check box to specify your own operating density. If you are doing natural convection with a pressure boundary, it's always a good idea to specify the operating density because you need it in order to specify the pressure on the boundary.

August 15, 2018, 07:49	Operating Density	#1
kr660170 New Member Karthik Join Date: Apr 2017 Posts: 29 Rep Power: 9	Hello Guys, Can someone explain me clearly what is the use of operating density that is found in the BC-Operating conditions?

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August 15, 2018, 10:55		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,672 Rep Power: 65	It's highly dependent on what models you have activated the purpose of the operating density. But presumably, you likely have gravity enabled and are using a Boussinesq model. The operating density would be the unperturbed density. You really should state what models you are using...

August 16, 2018, 03:24		#3
kr660170 New Member Karthik Join Date: Apr 2017 Posts: 29 Rep Power: 9	Thanks Lucky for your reply. I have defined density as piecewise-linear and i have enabled gravity Option. I am working on the Simulation of melting process of metal foam with Paraffin wax. So basically operating density is used when you define the density as boussineseq approximation right?

August 16, 2018, 11:16		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,672 Rep Power: 65	Whenever you enable gravity an operating density is needed. This density is needed due to hydrostatic effects (pressure changes due to elevation) which occur when there is gravity and because Fluent uses gauge pressures for BC's and so on. If you do use Boussinesq, you don't need the operating density because of the way Boussinesq works (operating temperature is the key parameter here). If you do not use Boussinesq, then operating density is needed. Fluent automatically takes an average pressure and uses it as the operating density unless you click the check box to specify your own operating density. If you are doing natural convection with a pressure boundary, it's always a good idea to specify the operating density because you need it in order to specify the pressure on the boundary.