Imbalance in transient simulation

Roland R · December 8, 2009, 10:50

Hi,

While the calculation is running, I always check the mass/energy imbalance and the mass flow at the inlet/outlet.

In steady state simulation there is not problem with these, but I don't understand what does the mass imbalance mean in the case of transient simulation. End of every timestep the imbalance is under 0.1% but the mass flow at inlet and outlet are different (for example 0.3kg/s @inflow and 0.35 kg/s @outflow).
How is this possible?

Regards
Roland.R

Attesz · December 8, 2009, 12:05

Hát ez tényleg elég érdekes, kíváncsi vagyok

ghorrocks · December 8, 2009, 17:55

Assuming your imbalances are small, in a transient simulation it means your modelled domain is loosing mass. This can only happen in a compressible simulation. If it is happening in a incompressible simulation then you have a problem.

Roland R · December 9, 2009, 06:39

I thought so

Thank you;

Roland R.

December 8, 2009, 10:50	Imbalance in transient simulation	#1
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	Hi, While the calculation is running, I always check the mass/energy imbalance and the mass flow at the inlet/outlet. In steady state simulation there is not problem with these, but I don't understand what does the mass imbalance mean in the case of transient simulation. End of every timestep the imbalance is under 0.1% but the mass flow at inlet and outlet are different (for example 0.3kg/s @inflow and 0.35 kg/s @outflow). How is this possible? Regards Roland.R

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December 8, 2009, 12:05		#2
Attesz Senior Member Attesz Join Date: Mar 2009 Location: Munich Posts: 368 Rep Power: 17	Hát ez tényleg elég érdekes, kíváncsi vagyok

December 8, 2009, 17:55		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Assuming your imbalances are small, in a transient simulation it means your modelled domain is loosing mass. This can only happen in a compressible simulation. If it is happening in a incompressible simulation then you have a problem.

December 9, 2009, 06:39		#4
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	I thought so Thank you; Roland R.