Negative mass flow rate

Lokesh · June 19, 2014, 12:09

Hi,
I am trying to check mass flow rate and am getting negative mass flow rate. For the same model if I am changing some boundary conditions such as pressure values I am getting positive values for some conditions. Why is this happening?
What I have to do if I get negative mass flow rate.

me3840 · June 19, 2014, 17:26

Negative mass flow rates just means the mass flow is going against the normal of the face of whatever you're measuring it on.

If you change pressure on the boundary conditions it's possible to reverse the direction of the flow.

You seem to be confused by something pretty fundamental. What are you trying to find out?

Lokesh · June 19, 2014, 18:12

Thanks for the reply. I am learning star ccm+.
I have modeled a body in which I am trying to give primary inlet pressure, secondary inlet pressure and exit pressure. I am checking for mass flow rate convergence. There for some boundary conditions I got negative mass flow rate.

me3840 · June 20, 2014, 15:47

That doesn't sound unreasonable. In general high pressure flows to low pressure. For certain pressures on your BCs it's possible for the flow to reverse direction. What's the problem?

June 19, 2014, 12:09	Negative mass flow rate	#1
Lokesh New Member Lokesh Join Date: May 2014 Posts: 6 Rep Power: 12	Hi, I am trying to check mass flow rate and am getting negative mass flow rate. For the same model if I am changing some boundary conditions such as pressure values I am getting positive values for some conditions. Why is this happening? What I have to do if I get negative mass flow rate.

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June 19, 2014, 17:26		#2
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 25	Negative mass flow rates just means the mass flow is going against the normal of the face of whatever you're measuring it on. If you change pressure on the boundary conditions it's possible to reverse the direction of the flow. You seem to be confused by something pretty fundamental. What are you trying to find out?

June 19, 2014, 18:12		#3
Lokesh New Member Lokesh Join Date: May 2014 Posts: 6 Rep Power: 12	Thanks for the reply. I am learning star ccm+. I have modeled a body in which I am trying to give primary inlet pressure, secondary inlet pressure and exit pressure. I am checking for mass flow rate convergence. There for some boundary conditions I got negative mass flow rate.

June 20, 2014, 15:47		#4
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 25	That doesn't sound unreasonable. In general high pressure flows to low pressure. For certain pressures on your BCs it's possible for the flow to reverse direction. What's the problem?