[bolbol]

Hi,
I was trying to assign the pressure and the mass flow rate at inlet for my case in Fluent, but after some research on the forums here, I've found that u can't do that because it's mathematically over specifying.


But someone suggest that i can use UDF to override this part, can this method work? and where exactly i just use it, in mass flow rate condition or in pressure-inlet condition?

[Kushal Puri]

Originally Posted by bolbol

Hi,
I was trying to assign the pressure and the mass flow rate at inlet for my case in Fluent, but after some research on the forums here, I've found that u can't do that because it's mathematically over specifying.


But someone suggest that i can use UDF to override this part, can this method work? and where exactly i just use it, in mass flow rate condition or in pressure-inlet condition?

This supersonic initial gauge pressure will come into picture only when your inlet flow is supersonic.

[bolbol]

Originally Posted by Kushal Puri

This supersonic initial gauge pressure will come into picture only when your inlet flow is supersonic.

what if my flow is subsonic?

[Kushal Puri]

Originally Posted by bolbol

what if my flow is subsonic?

It will use this value just for initial guess for the fast convergence, nothing else.

[bolbol]

Originally Posted by Kushal Puri

It will use this value just for initial guess for the fast convergence, nothing else.

then it's impossible even with using UDF ?

[Kushal Puri]

Originally Posted by bolbol

then it's impossible even with using UDF ?

Actually defined both the pressure and mass flow as inlet is over constrained inlet boundary condition. I think fluent will not take it

[Goaksy]

Originally Posted by Kushal Puri

This supersonic initial gauge pressure will come into picture only when your inlet flow is supersonic.

SO on a similar note, I want my inlet to be supersonic and I do not know the pressure but only mass flow rate. what do I do ?

I have a compressible flow 2D simulation.

[LuckyTran]

You need to figure out what Mach number you want. Otherwise, any Mach number greater than 1 is supersonic and there are infinitely many conditions that will be supersonic and give you a mass flow rate.


Once you pick a Mach number, a specific masss flow rate will dictate the static pressure.

[Goaksy]

Sir the case is something like this.
A density based, steady state, RANS averaged, non reacting(cold flow simulation), 2d planar, Spalart Allmaras viscosity model. The air and fuel inlets are perpendicular to each other.
The inlets are mass flow inlets(known from the source paper). Here I have turned on turbulence intensity and hydraulic diameter condition and set the intensity to 5%.
The materials air is ideal gas and viscosity constant. Mixture hydrogen air density is constant and viscosity ideal gas mixing law.
The outlet is a pressure outlet constant at 1 bar ( how do I keep this ? For some simulations I tried I had kept gauge pressure and pressure as absolute pressure).
Should I also turn on prevent backflow and target mass flow rate ?
The fluid domain is then initialized with equivalence ratio 0.6.

The paper says for the mass flow rate inlet of air of 0.5kg/s the highest mach obtained is 1.21.
Till now in the flow domain the highest mach obtained is 0.54. We are not understanding where we are wrong. Can you please help us and if you dont mind please share your mail id, it will be easy for me to share the case details.
This is for my college project and the deadline is in 72hrs 😵

[LuckyTran]

If it's a college project then you have paid instructors to answer your questions 24/7. Maybe use the resources which you've paid for.


Mach number inside domain means nothing for the inlet. You need the inlet Mach number. And do not use a mass flow inlet and a mass flow outlet, pick one. Fluent always uses gauge pressures, you just have to deal with it. Only thing you can maybe do is set the operating pressure to 0 but it is still technically a gauge of 0.