Flow measurement via sensor Flow simulation & asymmetry of results

Hello

I am asking for your help to find a trick to measure a flow rate through a "sensor" part in Solidworks flow simulation.

Please find attached a view of the simulation result of my concept. Fluid used: air. Boundary conditions: Inlet flow rate on the left of 8735 kg/h and outlet flow at the other end, a pressure of 20mbar.

I would like to measure the air flow that would come back to mix with the primary flow in a fireplace (the place where the velocities are negative in X). I created circular sensors along my "recirculated" flow. On the other hand, the flow rates indicated seem inconsistent to me:

 

We clearly see an inconsistency on one unit, we measure a flow rate higher than the inlet condition which is 8735 kg/h. The other speeds also seem high to me.

Do you have any tricks or other methods that would measure my desired flow rate? (Ideally, you should keep the values in mass flows). In addition, I was able to observe a slight asymmetry of the flow while my model is totally symmetrical Do you know where this could come from? (Calculation performed in transient over 10 seconds with a step of 0.01 seconds & level 2 automatic refinement. The mesh seems to me to be fine enough)

Thank you for your answers.

Kind regards

Can you repost photos 1 and 2 in a little bigger?

Hello, below are the 2 images in a "ZIP" archive. In the meantime, I had the technical support who told me an asymmetry due to a turbulent flow.

 


images.zip

In general, in aeraulic systems, a perforated sheet is laid at least at a distance of 5 d to try to have a laminar flow