[sameerhad12]

I am trying to simulate the flow of air inside a rectangular 2D geometry (slightly tapered at the end). I give the initial value of pressure about 261kPa in solution initialization and in the inlet boundary condition. but after the solution is converged the results are totally absurd. In final results the initial value shown is about -0.5 bar at the inlet which does not matches with the already given inlet boundary conditions. Please help me out

[LuckyTran]

Make sure you realize there are two inputs. The actual pressure boundary condition and an initial (gauge) pressure.

For subsonic flows, the supersonic / initial gauge pressure dialogue box is not a boundary condition.

The value in that box is used only for initialization AND only if you "select from" that boundary. Otherwise, the initial pressure is from something else (the user set value if you use standard, or whatever boundary was actually selected)

Other than initialization, the value that is in the initial gauge pressure dialogue box is moot, it does nothing.

[sameerhad12]

thanks you for your answer but I already try this but I get the same absurd results. Please tell me that what boundary condition I will give at outlet? I am using a pressure outlet condition with 0 gauge pressure at outlet. at inlet I am giving velocity inlet condition with 2.6 bar at inlet

[LuckyTran]

Originally Posted by sameerhad12

thanks you for your answer but I already try this but I get the same absurd results. Please tell me that what boundary condition I will give at outlet? I am using a pressure outlet condition with 0 gauge pressure at outlet. at inlet I am giving velocity inlet condition with 2.6 bar at inlet

I have no idea what you mean by absurd but... can you clarify how you specify both velocity and pressure? Is 2.6 bar the static pressure or stagnation/total pressure?

What is your equation of state?

Did you remember stagnation temperature also?

Velocity inlets are tricky because they can easily end up being ill-posed. The problem is probably the velocity inlet and not the pressure outlet, unless you have like a choked flow then the pressure outlet can be anything and your flow is determined only by upstream conditions. Anyway, lots of scenarios to consider.

[sameerhad12]

here I attached the boundary conditions of air T0 and P0 are stagnation and T and P are static

[LuckyTran]

But what did you specify in Fluent? You can't specify all 5 of those things, only 3 of them.

What is your equation of state? Depending on which EOS you use, you may also need to set the operating pressure.

[sameerhad12]

I specify only static conditions i.e of pressure, temperature and velocity. I am only using ideal gas law as EOS i.e pV=mRT. The operating pressure is 1 bar i.e atmospheric, it is taken as default value.I didn't disturb it. will it effect the simulation?