Learning Forum

[rajendrapor]

Hello All, 

How can I extract the mass flow rate data at a cross-section of my geometry in a transient simulation?

I have tried to make a monitor of Report--->Flux----> Mass flow rate. However, it does not show any change in the mass flow rate with time.

I am simulating an oscillatory system with pressure as inlet BC.

[Rob]

If you plot images is the result changing? 

[rajendrapor]

Hi Rob. Thanks for the quick response.

I am using a sinusoidal pressure inlet udf as BC for my system. I want to extract the data at a particular cross section. But it remains at zero with the simulation time (as attached in the figure). By plotting the images, what exactly do you mean? Should I plot the contours?

 

[Rob]

Yes, velocity contours. If you didn't set the report up correctly (ie using an area value for a point monitor) it's very possible to get a zero value on the monitors. 

[rajendrapor]

Hi Rob, 

Yes, I am able to plot velocity contour plots. Attached is an example of the velocity plot (after extracting data from Fluent). I am not able to figure out why the mass flow rate is zero, the expected behavior is that it should give me a sinusoidal function.

 

[Rob]

That looks like you have a velocity field. How is the report defined? 

[rajendrapor]

I have tried to make a monitor of Report--->Flux----> Mass flow rate, at a cross-section of my model geometry. 

[Rob]

On an iso-surface or a named mesh (interior) face? If you report mass average of velocity on that surface what do you get? 

[rajendrapor]

I am trying to monitor the mass flow rate at the named (mesh-interior) face. I will monitor the mass average of velocity and let you know as soon as possible. 

[Rob]

No need to monitor, just create the report and check the value. This is to get an idea of whether there is flow, ie if there's a problem with the model rather than the report. Similarly run the mass flow report at the current time and see what value is posted to the TUI. 

[rajendrapor]

Okay. Although I monitored the flow also. and got something like below. I checked the values also and I am getting the values correctly. I don't know why my mass flow rate is showing as zero on the monitor. Since I need to save data for every time step.

 

 

[Rob]

If you open the mass flow report there should be a calculate or display button. What value does that post to the TUI?

[rajendrapor]

It is displaying 0 kg/s. However, at the inlet, I am getting a mass flow rate of 0.00053036776 kg/s. 

[Rob]

Odd, what about the outlet?

[rajendrapor]

There is no outlet in the system. It is a closed system, in which the flow gets reversed.

[Rob]

OK, so why wouldn't mass flow be zero? 

[rajendrapor]

Meaning thereby? 

Due to the closed system, the mass flow rate is zero?

[Rob]

Yes, if the density is fixed then you should have a zero mass flux. What goes in comes out.