[jonior]

hi every ,

iam simulating a nozzle ,i am using a compressor and pressure control gauge the pressure coming into the nozzle inlet from the compressor is 0.5bar

how can i put this value in the boundary condition (pressure inlet)
i mean that there are 3 sections in pressure :
1- operating pressure (in operating condition)
2-gauge total pressure
3-supersonic/initial gauge pressure

i am confused i dont know how to put the correct value in every section

pls hlp
thanks

[ghost82]

Hi,
I think you can define operating pressure condition to atmospheric (101325 Pa).
Gauge total pressure is defined by the sum of static pressure + kynematic pressure - operating pressure (for an incompressible fluid), or is a function of static pressure, mac number and gamma (cp/cv) - operating pressure for compressible fluids (constant cp).
If your fluid is not supersonic then the supersonic/initial gauge pressure is not important, so I usually input a value slightly lower then the total pressure (I remember I read it somewhere in fluent user guide).

So let's say you are simulating an incompressible fluid with inlet pressure (static pressure) = 0,5 barg (1,5 bar) and an inlet velocity of 10 m/s.
Operating pressure: 101325 Pa
Gauge total pressure: 1,5 bar + 1/2*rho*10^2 - 101325 Pa = 48769 Pa (assuming density 1,88 kg/m3)
Initial gauge pressure: 45000 Pa

[jonior]

i am using compressible ideal gas flow ???????????/
and my only data is the inlet pressure .5 bar and the diameter of the nozzle (inlet) is 0.5mm
could you pls hlp

[ghost82]

Read here for compressible fluid and total pressure equation. You need to calculate mach number and gamma at your inlet:
http://aerojet.engr.ucdavis.edu/flue...ug/node219.htm

[jonior]

i know that iam asking tooooo much pls dont be anger from me ,

1-in my case what is the value of static pressure (or equation to calculate)when my pressure inlet from the compressor is 0.5 bar
2- Cp for ideal gas=1006, but how can i get Cv to calculate gamma

[ghost82]

For an ideal gas cp=cv+R where R is the universal gas constant and cp and cv the molar heat capacities.
If the manometer is mounted perpendicular to the flow direction you can assume what you read is the static pressure.
Static pressure means pressure measured in static condition (as the fluid doesn't move).
I'm writing mounted perpendicular to the flow because in that condition you can assume that dynamic pressure (relative to the fluid velocity) is negligible when it is measured from the manometer.

[jonior]

Originally Posted by ghost82

If the manometer is mounted perpendicular to the flow direction you can assume what you read is the static pressure.
Static pressure means pressure measured in static condition (as the fluid doesn't move).
I'm writing mounted perpendicular to the flow because in that condition you can assume that dynamic pressure (relative to the fluid velocity) is negligible when it is measured from the manometer.

i am using pressure gauge controller In the
measurements, the device was placed between the compressor and the nozzle. should i use manometer ,doesn't the regulator enough

[ghost82]

Condider what you are reading as static pressure.

[jonior]

thank you a lot for your help ,i hope you help me in other problems in this simulation in the boundary conditions
1-i have 4 pressure inlets (injectors)with the same pressure guage (0.5bar)
2- the main opening is (pressure inlet) atmospheric pressure
3-the outlet is (pressure outlet) atmospheric

my question is in fluent:
1- when setting refernce value which place should i use
2-in solution initialization compute from where? (which boundary)

[ghost82]

1- Reference values are used to calculate some parameters such as Cd, Cl, etc. and they are not used to compute the solution; you have to set them only if you have to calculate parameters that use them.
2- You can do an hybrid initialization for your case; if you study the steady state solution no matter what are the initial conditions, the solution should converge to a unique solution indipendent of the initial conditions; however, setting properly initial conditions helps the convergence of the solution.

Please don't cross post, as per forum's rules.