Mass loss in exported inlet profile

Pheasants · April 14, 2013, 03:11

Hi guys,

I'm simulating a combustion in a combustor chamber with fluent.
Since the combustor's geometry is big, I divided the simulation into cold flow for the whole geometry, and later on hot flow for only small part of the geometry.

I exported the boundary profile from the result of the cold flow simulation (omega, k, v-x,y,z) with CFD-post, at some surface location (made with plane and surface revolution) , and use it as velocity inlet profile for the hot flow simulation at the exact same location.

Now, the intended convergence level is not yet satisfied, but there is apparent decrease in the mass flow rate (initially inlet mass flow rate was 0.0375 in, but after it was exported at several cutting location, it decreases into 0.0369).

Can anybody tell me why is this happening?

Thanks a lot guys.

Pheasants · April 15, 2013, 06:43

Hello guys..

Apparently the incorrect mass flow is coming from the cfd-post itself..

The massflow difference between inlet and outlet is less 0.0002% (which basically, no difference)..

But when I Define a surface, for example, 5cm from the inlet surface (with the same area), and then I calculate the massflow, the value changes.. and the massflow difference between the inlet and the newly defined surface is 0.8%, which is ridiculously huge..
If I define another surface, say now its 10 cm from the inlet, the mass flow changes again..

Do anybody know why was this happening? was it because the hybrid or conservative value used by the fluent solver?

thanks a lot guys.

April 14, 2013, 03:11	Mass loss in exported inlet profile	#1
Pheasants New Member Riza Yukananto Join Date: Mar 2013 Posts: 4 Rep Power: 13	Hi guys, I'm simulating a combustion in a combustor chamber with fluent. Since the combustor's geometry is big, I divided the simulation into cold flow for the whole geometry, and later on hot flow for only small part of the geometry. I exported the boundary profile from the result of the cold flow simulation (omega, k, v-x,y,z) with CFD-post, at some surface location (made with plane and surface revolution) , and use it as velocity inlet profile for the hot flow simulation at the exact same location. Now, the intended convergence level is not yet satisfied, but there is apparent decrease in the mass flow rate (initially inlet mass flow rate was 0.0375 in, but after it was exported at several cutting location, it decreases into 0.0369). Can anybody tell me why is this happening? Thanks a lot guys.

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April 15, 2013, 06:43		#2
Pheasants New Member Riza Yukananto Join Date: Mar 2013 Posts: 4 Rep Power: 13	Hello guys.. Apparently the incorrect mass flow is coming from the cfd-post itself.. The massflow difference between inlet and outlet is less 0.0002% (which basically, no difference).. But when I Define a surface, for example, 5cm from the inlet surface (with the same area), and then I calculate the massflow, the value changes.. and the massflow difference between the inlet and the newly defined surface is 0.8%, which is ridiculously huge.. If I define another surface, say now its 10 cm from the inlet, the mass flow changes again.. Do anybody know why was this happening? was it because the hybrid or conservative value used by the fluent solver? thanks a lot guys.