[Dknot]

Hello!

I am new with CFD and fluid dynamics. My question is about steady state velocity profiles of air bursts into tank:

As seen in attached image I have two situations: In first one, I have air bursting to tank with 1,9m/s speed. Pressure in tank is quite low, 10mbar (=10hPa).
In second situation, I have air bursting with same 1,9m/s speed, but pressure of tank is different, 1 atm (normal air pressure).
In both situations air goes out from small holes up in tank. Gravitation is neglected in this situation.

So, everything remains the same except pressure in tank. However, velocity profiles are completely different as seen in figures below. Velocity profile plots are horizontal cut lines in y=0,03m.
I am quite sure that profile is different because density of air is smaller in 10mbar pressure. I still lack any concrete mathematical evidence why profile is so different.

So my question is: Why profile is so different? Why there is recirculation zone in 1atm simulation but no recirculation zone in 10mbar simulation? Any references to links that explain this phenomenom would be appreciated because I would really want to understand this phenomenom.

Thanks alredy for answers and follow up questions,

-Dknot