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Old   March 2, 2005, 09:28
Default OPERATING PRESSURE
  #1
manish
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Hello All,

I was wondering how to set my operating pressure and pressure inlet and outlet:

I have a chamber which is initially pumped down to .1 psi, and then i have a nozzle that has supersonic air flowing into the chamber at 180 psi.

I have set the operating pressure as .1 psi, and the boundary conditions for pressure inlet and outlet accordingly.

i haven NOT specified a location for the operating pressure, and I hope it uniformly is distributed along the whole chamber? does anyone know if this is the right approach?

hope to hear from somoone soon.

Thanks. -manish
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Old   March 2, 2005, 10:07
Default Re: OPERATING PRESSURE
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manish
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If someone could let me know how I should setup this problem, I would appreciate it.

i basically have a near vacuum chamber(.1psia) and I am flowing air through a supersonic nozzle.

i have done it in a particular way, but I do not know if this is correct.

hope someone can help me. please. manish
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Old   March 3, 2005, 05:49
Default Re: OPERATING PRESSURE
  #3
Melaku H.
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The information you provided is a bit scketchy, like whether your simulation is steady or transient...? Ideal gas model? but I would try the folowing:

1. I think you wanted to the near vacuum condition to increase the overall pressure ratio..I may be wrong here. In any case it would be IMPOSSIBLE to use the floating operating pressure even if you have a transient condition since you said U have a pressure inlet and pressure outlet B.C.

2. If it is a steady state simulation then I would try to set the operating pressure to be the mean absolute pressure of the flow. It also depends on the type of model you choose...incompressible ideal gas, or ideal gas itself. I'm assuming the flow will be compressible and may be with a shock somewhere.

Last but not least if your flow is in the high-Mach number, then Operatign pressure is less significant and you can simply use Guage Pr = Absolute pressure....round off errors are not that significant for this particular flow.
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Old   March 3, 2005, 05:50
Default Re: OPERATING PRESSURE
  #4
Melaku H.
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Hi,

The information you provided is a bit scketchy, like whether your simulation is steady or transient...? Ideal gas model? but I would try the folowing:

1. I think you wanted to the near vacuum condition to increase the overall pressure ratio..I may be wrong here. In any case it would be IMPOSSIBLE to use the floating operating pressure even if you have a transient condition since you said U have a pressure inlet and pressure outlet B.C.

2. If it is a steady state simulation then I would try to set the operating pressure to be the mean absolute pressure of the flow. It also depends on the type of model you choose...incompressible ideal gas, or ideal gas itself. I'm assuming the flow will be compressible and may be with a shock somewhere.

Last but not least if your flow is in the high-Mach number, then Operatign pressure is less significant and you can simply use Guage Pr = Absolute pressure....round off errors are not that significant for this particular flow.

Melaku H.
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Old   March 3, 2005, 09:06
Default Re: OPERATING PRESSURE
  #5
manish
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I apologize for that.

It is steady state and attains a mach exit of 5.0. I have set the operating pressure as the overall pressure of Mars(or our chamber setup). Is this correct? It is Nitrogen that I am using.

Thank you for all your help. -manish

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Old   March 3, 2005, 17:28
Default Re: OPERATING PRESSURE
  #6
Melaku H.
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Hi,

The fact that you have steady state simulation throws floating operating pressure out - not applicable. So now you left with a high Mach number (still less than hypersonic range or I would say lower end of it) steady flow simulation. Its a much easier case than the transient condition - transient is a headache in such conditions. So I don't see any problem here as long as you have a sound convergence. If you still have doubts about your results, I would say check the mesh dependency of your soulution (i.e see if change in mesh size affects your soln...repeat it till u see no change in solution - this is pretty standard way of checking ur answer, the closest u can get, if u don't have experimental result) and Its also wise to have somewhat strict convergence criteria..etc

rgds

Melaku H.
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Old   February 25, 2011, 05:40
Post hypersonic inline inlet
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Vivek V.Kumar
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Hi,
Even I am having a doubt in setting the operating pressure. I am simulating a hypersonic inline inlet at mach no.= 7 at an altitude of 35 km.
I have taken solver as density based, implicit,2D , steady, absolute.
Density as ideal gas and tried with operating pressure of 0 atm.
My results are not converging...
I ve even tried to give the density as constant and input the value at std. atmospheric condition.... but no result. Could u pls help me to solve it.
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