Why negative pressure at inlet in backwardFacingStep2D tutorial?

bobuhito · May 5, 2022, 10:30

Right out of the box, this tutorial simulates a negative inlet pressure
(inlet P/rho = -41 m^2/s^2, outlet P/rho is zero) though it forces a positive
inlet velocity (44.2 m/s). Is this some problem with the turbulence model,
or am I going crazy (this seems to defy conservation of energy)?
I'm using openfoam2112.

bobuhito · May 6, 2022, 01:03

Nevermind, my mistake. In short, this reverse pressure gradient is explained just
with Bernoulli's principle. As for energy, somewhere outside of the simulation
(i.e., before the inlet), the pressure must be positive (i.e., greater than the outlet
pressure) to have gotten the air moving at its high inlet speed. It all seems pretty
obvious now.

May 5, 2022, 10:30	Why negative pressure at inlet in backwardFacingStep2D tutorial?	#1
bobuhito New Member BH Join Date: Dec 2021 Posts: 9 Rep Power: 4	Right out of the box, this tutorial simulates a negative inlet pressure (inlet P/rho = -41 m^2/s^2, outlet P/rho is zero) though it forces a positive inlet velocity (44.2 m/s). Is this some problem with the turbulence model, or am I going crazy (this seems to defy conservation of energy)? I'm using openfoam2112.

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May 6, 2022, 01:03		#2
bobuhito New Member BH Join Date: Dec 2021 Posts: 9 Rep Power: 4	Nevermind, my mistake. In short, this reverse pressure gradient is explained just with Bernoulli's principle. As for energy, somewhere outside of the simulation (i.e., before the inlet), the pressure must be positive (i.e., greater than the outlet pressure) to have gotten the air moving at its high inlet speed. It all seems pretty obvious now.