What happen with the scale of pressure?

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 October 14, 2008, 15:11 What happen with the scale of pressure? #1 Kostas Pan Guest   Posts: n/a i have problem with the scale of static pressure of a flow. it is show me big negative values of pressures. For example: In a pipe i put inlet pressure 40000Pa(approximately 0.4 atm) and outlet pressure 200000Pa(approximately 2 atm) and fluent show me values of pressure until -700000Pa (approximately 7 atm). How can it be occured this? If we have inlet pressure 0.4 atm then the minimum value can take the fluid is 0 atm.

 October 15, 2008, 03:48 Re: What happen with the scale of pressure? #2 devesh Guest   Posts: n/a Hi, The Inlet pressure you are giving is Static or Total Pressure ? is the same case for Outlet condition ? Did you check the Total/Static/ Dynamic pressure values after getting the solution ? you provided Pinlet = 0.4 atm, Poulet = 2 atm. in that case direction of flow will be completly reverse. In that Pinlet(0.4 atm is Total pressure) will be decomposed into two component:- Static Pressure & Dynamic Pressure. Please check those values. Are they give 0.4 atm by summing up Static & Dynamic pressure in the solution. I guess that will be helpfull, please fell free to ask if I can you help you in better way

 October 15, 2008, 05:24 Re: What happen with the scale of pressure? #3 Kostas Pan Guest   Posts: n/a hi devesh. In the box of Pressure inlet of Boundary contitions there are two options: "Gauge total pressure" and "Initial gauge prssure". I use the second option for static inlet pressure. This is right? Still, i want to ask you, why is there the "operation condition". if i put a value of prssure in the operation condition, this value where will apply? I don't unstarstand where useful this.

 October 15, 2008, 06:05 What happen with the scale of pressure? #4 devesh Guest   Posts: n/a Hi Kostas, Operating Pressure is Standard Pressure(i.e. 1 atm by default). Now what-ever pressure you put, that is Gauge pressure. You put 0.4 atm in Gauge Total Pressure (total pressure= static pressure + dynamic pressure). Fluent works on Absolute Pressure(i.e. Operating pressure + gauge pressure). If you want to know more about Pressure , Please go through FLuent User Guide, that will help you alot. By chance if u want to run your analysis, you put 0.4 atm in Gauge total Pressure. "Initial gauge Pressure" is for initial guessing & is used in case of Compressible Flow. best of luck......

 October 15, 2008, 11:16 Re: What happen with the scale of pressure? #5 Kostas Pan Guest   Posts: n/a Ok. i understand! In the box of operating condition there are X: and Y:. What mean that? That on this point we will have the operation condition? If define aq point which find out of geometry what mean?

 October 16, 2008, 03:07 Re: What happen with the scale of pressure? #6 devesh Guest   Posts: n/a Hi, I think you are talking about Reference Pressure Location !....If you have been scaled your geometry & if this is not a very complex flow condition then leave it as default value of Zero. If I am correct to understand your problem, then it is the location from where solver consider it as a reference point to adjust the Numerical Pressure with respect to surrounding cell centre. If I am misleading something, pls correct me.

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