Learning Forum

[manu prabha anand]

I have a doubt regarding porous media simulation. I have attached the test case files for both simulations in google drive.  https://drive.google.com/drive/folders/1NNz9imRNjz9gyQAT6GyXcdsRLZtUadOK?usp=share_link

[manu prabha anand]

[manu prabha anand]

[manu prabha anand]

[manu prabha anand]

[manu prabha anand]

What is my error?

[Rob]

If you plot pressure drop with velocity to create the porous coefficients (or use an alternative way to determine these) what do you get? The plot doesn't tally with what I'd expect. 

What material is flowing? Why set the operating pressure to zero? 

 

[manu prabha anand]

Air is the fluid.

When i use experimental data as shown in figure, to get plot with that plot i fit the curve using polynomial as shown , then i used that to relate with darchy equation to get the data. Do you have any tutorial for porous media calculation? Even if i give ansys default porous media properties, nothing changes. the result is same. I tried even fine structured mesh also.Nothing changes.

Operating pressure is set to zero because the calulation should be on absolute pressure condition. What is the difference when operating pressure is changed. Do i have to keep operating pressure 8bar? I have tried that also.no change in result.

[manu prabha anand]

What about operating condition?

[manu prabha anand]

but when i do Pressure inlet and mass flow outlet the result is what I expected. Is this boundary condition good or not.

[Rob]

And the air density? 

[manu prabha anand]

https://forum.ansys.com/forums/topic/fluent-simulation-i-am-getting-error-in-pressure-incompressible-pipe-flow/

Air density do not know for comprssed gas at 8 bar we can calculate but uncertain over the flow in this condition, which in real application it must be varying, because it is cooled, but similar problem with  a pipe plow also i had posted it earlier that case it is impressile flow, it has constant air density. This also same with a simple pipe flow iposted earlier, that also in compressible flow we can consider contant density of 1.22kg/m3, but that also same results , error in pressure calculation? why? This preoblem also solved with pressure and mass flow outlet condition.

 

[manu prabha anand]

https://drive.google.com/drive/folders/1NNz9imRNjz9gyQAT6GyXcdsRLZtUadOK?usp=share_link

[manu prabha anand]

what is the error in the above simualtion?

 

[manu prabha anand]

if i know only inlet mass flow rate and outlet properties are not known, how to give inlet mass flow rate 3.7kg/s and pressure 9 bar, but on computation , i give superonic gauge pressure is 9 bar, but on calculation why the property change?

[Rob]

What error? You did read what the supersonic pressure is for? 

[manu prabha anand]

yes, I have read it before. 

"The static pressure (termed the Supersonic/Initial Gauge Pressure) must be specified if the inlet flow is supersonic or if you plan to initialize the solution based on the pressure inlet boundary conditions. 

The Supersonic/Initial Gauge Pressure is ignored by ANSYS FLUENT whenever the flow is subsonic. If you choose to initialize the flow based on the mass flow inlet conditions, the Supersonic/Initial Gauge Pressure will be used in conjunction with the specified stagnation quantities to compute initial values according to isentropic relations."

My question is if i know a gas flow mas flow rate, in which the pressure of the gas is 9 bar, how to fix mas flow rate and pressure at the inlet. I have given 9 bar supersonic gauge for initialization, but i had calculated density for 9 bar using (rho=P/RT) and given the density to the fluid medium constant. " if i give density constant to fix the pressure of the flowing fluid. what is the error in my input? Am

[manu prabha anand]

I am asking, Am i doing correct or not? 

[Rob]

You don't set the inlet pressure, it's based on the local flow field. If your whole system is at elevated pressure you may be able to use fixed density. The operating pressure mimics the atmospheric pressure and boundaries are then set at gauge relative to the operating pressure. If the system is truely compressible, then zero operating pressure and setting the boundaries can be more stable. 

Note, the initial condition is just that. Once the solver has done some iterations it's no longer going to show the initial conditions in the results.