Learning Forum

[chiragthakar29]

The room has basically three components inlet, outlet and rest is wall. I want to create negative pressure in compare to the outside of the room. I am having two fans one at inlet and one at outlet. I want to know the inlet velocity and outlet velocity which can lead to this neagtive pressure generation.nAs 1 atm = 101325 PanI want to generate only pressure of 101300 Pa.nI am confused that what to take the boundary conditions of the inlet and outlet so that I can get the required pressure results.nn

[Rob]

Negative pressure compared to what? What are you using for air density, and what do you expect to see with a negative pressure?n

[chiragthakar29]

Negative pressure in compare to outside of the room.nThe default fluid air is taken into consideration.nI only want to make the negative pressure inside the room constant with respect to time..that is what I want to see..n

[Rob]

If you suck the air out of the room (negative velocity) and use a pressure boundary at ambient on the inlet that may give you want you want. Using two fixed flow boundaries in a steady state model will give either zero or infinite pressure. n

[chiragthakar29]

I did as you guided me sir, but I am getting -10 Pa pressure even if I am taking a very less outlet velocity like 1m/s. I am attaching certain photos so that you get an idea about my simulation.nInlet velocity is coming around 4m/s.nThe main concern is that why the pressure is coming like -10Pa . I want attain a constant 101300 Pa which is only 25 Pa less than atmospheric pressure. nPlease help.nnn

[Rob]

If you want -25Pa you may need to suck more air out, so increase the flow rate. You did read the manual section(s) explaining how the operating pressure worked didn't you?n

[chiragthakar29]

Does in CFD post when we select the contour and select in it to show pressure, it shows gauge pressure?n

[Rob]

Why? If atmospheric pressure is 101325Pa what is the difference between -25Pa Gauge and 101300 Pa absolute? n

[chiragthakar29]

Yes, I got your point . Thank you for your guidancen