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 solomedic August 27, 2011 05:29

Reference Pressure CFX

I am doing flutter analysis of AGARD 445.6 wing. all physics has been developed and I am sure that all settings are correct. the only problem that I am getting is setting the pressure. I have a reference pressure in default domain>basic settings and a reference pressure in air as ideal gas so what these pressure signifies? which pressure is used to find density. for density we use absolute pressure which is sum of reference and static pressure? from where I will get static pressure?

lets sum up. I want to have a dynamic pressure of 4500 Pascals at .9 Mach using air as ideal gas so what pressures and temp should I use? Kindly reply this is very Important:confused:

 ghorrocks August 27, 2011 07:15

Density is calculated on absolute pressure. The absolute pressure is the sum of the reference pressure (the one on the domain tab) and the pressure variable (which is static pressure).

Please do not hijack multiple threads with the same post again. It is a misuse of the forum. I have removed all the duplicate posts.

 solomedic August 27, 2011 12:40

Reference Pressure CFX

I will not post same message to multiple threads, I just did it to get an reply from immediately.
thanks ghorrock for the help but my question remain unanswerd

I need dynamic pressure of 4500 pa at Mach .9????

I used air as ideal gas and its reference pressure is 1atm not the one at basic settings tab. reference temp is 298k. assuming that velocity at .9Mach is 270m/s or any value you would suggest?

SO what reference Pressure now I should use at default domain>basic setting? to get dynamic pressure of 4500 pascals at velocity of 270m/s.

 ghorrocks August 28, 2011 06:46

A dynamic pressure of 4.5kPa where? At the inlet? At a specific point in the domain? Isn't this simply a matter of setting the inlet velocity to a appropriate value to get the correct dynamic pressure?

Set the reference pressure to be the ambient pressure, so atmospheric (if in the atmosphere) or the wind tunnel down stream pressure (if a wind tunnel).

 solomedic August 28, 2011 23:37

Reference Pressure

Thanks ghorrocks for reply. a dynamic pressure of 4.5kpa at wing or for simplification make it at inlet. Velocity I thought as well to just change it to match the dynamic pressure but I have to at Mach .9 as well, so the relation v=M*sqrt(gamma*R*T) must all to be specified.
Now can you suggest some velocity at inlet and some reference pressure? I am stuck and very few days are left to pressent this work.

 ghorrocks August 29, 2011 18:50

As I said, the reference pressure should be set to the atmospheric pressure.

It sounds like your condition of Ma=0.9 and dyn pressure of 4.5kPa can be evaluated to define the velocity, density, pressure and temperature of the inlet boundary. Then I would use a simple inlet boundary with velocity and temperature defined and an outlet at 0 pressure.

 solomedic August 30, 2011 10:48

thats what I cant understand that how the dynamic pressure and Mach can be translated to inlet velocity,temp etc.????? can you tell how can I find inlet velocity from these conditions

 ghorrocks August 30, 2011 19:00

That is just basic fluid mechanics from the definitions of Mach number and dynamic pressure, and anything else you already know about the flow.

 acd January 6, 2013 14:30

Hi solomedic,

Did you find a way to change the dynamic pressure for your analysis.

I am currently doing the same AGARD 445-6 analysis (ANSYS 14) and am struck at the same place. I have used the data from the literature for velocity, dynamic pressure and input them at the default domain setting for reference pressure and velocity value for inlet velocity, but I am not able to get the flutter characteristics as found in the experimental result.

If you have solved the problem can you please guide me on how you achieved it.

Regards
ACD

 solomedic January 7, 2013 02:06

Quote:
 Originally Posted by acd (Post 400347) Hi solomedic, Did you find a way to change the dynamic pressure for your analysis. I am currently doing the same AGARD 445-6 analysis (ANSYS 14) and am struck at the same place. I have used the data from the literature for velocity, dynamic pressure and input them at the default domain setting for reference pressure and velocity value for inlet velocity, but I am not able to get the flutter characteristics as found in the experimental result. If you have solved the problem can you please guide me on how you achieved it. Regards ACD
ok thats good to see, someone else also doing the same project. its been over 1 year I have done it, so dont exactly remember it, but found the method to how to set the pressure over the wing. it was a hit and trial type method. you have to specify a point over a wing and set the tracker to total pressure. track it during run, if it match the experimental value continue the run, if not change the atmospheric pressure to match the value.

 Jordane August 1, 2014 05:19

Quote:
 Originally Posted by solomedic (Post 400410) ok thats good to see, someone else also doing the same project. its been over 1 year I have done it, so dont exactly remember it, but found the method to how to set the pressure over the wing. it was a hit and trial type method. you have to specify a point over a wing and set the tracker to total pressure. track it during run, if it match the experimental value continue the run, if not change the atmospheric pressure to match the value. you can contact me on muhammadaamir38@yahoo.com, hope I will be able to help you better
Hi solomedic
I also do the agard 445.6 wing flutter analysis but get stuck wth setting the reference pressure, density and velocity in CFX. Could you tell me how to do that?

 solomedic August 1, 2014 06:39

Quote:
 Originally Posted by Jordane (Post 504020) Hi solomedic I also do the agard 445.6 wing flutter analysis but get stuck wth setting the reference pressure, density and velocity in CFX. Could you tell me how to do that?
Nice work Jordane, it's been long time I have done it. I couldn't completely remember how I done it, but it was more of trial and error sort of method. You have to change total pressure at input and monitor dynamic pressure at the wing, continue playing with total pressure until you get the desired dynamic pressure. another guy also asked the same question in this post, Hopefuly hecan answer u better. Kindly share if you find the way. Feel free to ask if u are stuck somewhere

 Jordane August 3, 2014 05:22

Quote:
 Originally Posted by solomedic (Post 504035) Nice work Jordane, it's been long time I have done it. I couldn't completely remember how I done it, but it was more of trial and error sort of method. You have to change total pressure at input and monitor dynamic pressure at the wing, continue playing with total pressure until you get the desired dynamic pressure. another guy also asked the same question in this post, Hopefuly hecan answer u better. Kindly share if you find the way. Feel free to ask if u are stuck somewhere
Hi, solomedic. Thank you for your reply. As you mean, I have to do the Steady-state analysis with the wing and monior the dynamic pressure, but how do I setting the initial condition for CFX-Pre with Steady-state analysis ?

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