Hello,

I am currently working on a simple convergent-divergent nozzle, with the following characteristics: -radius inlet&outlet=0,5m -radius throat =0,1m -Pin=20 bar -Tin=3424K -The fluid is water vapor (considered as ideal-gas and Cp=3225J/kg.K)

I used the coupled implicit axisymetric solver on a 2D mesh and tried to evaluate the influence of the different models (inviscid, S-A and RNG k-e) and meshes size (750, 3000 and 12000 cells), considering the fact that i have to output the mass flow rate and the velocity at the outlet and compare it with the following results: MFR=32,0893 kg/s Uex=3145,86 m/s

The Boudary Conditions are: -Pressure inlet (Po=20bar, P=19,5, To=3424K) -Pressure outlet (Pg=1bar) -Axis on the symetry edge. -Wall

I reached good comparative results with the 2 first meshes but for the last one (12000 cells) with the laminar and RNG k-e model, the Uex stabilize at 2300m/s and it seems that recirculation occurs (I have a reversed flow on the Pout and the velocity vectors show a region of recirculation near the wall at the exit). How can I obtain good results on this mesh? Do i need to refine the mesh near the recirculation? or do you think, the problem is related to the turbulence model?

If someone have any suggestions or hints,i would be very grateful. Regards

Jeremie

Hello jeremie I modeled 2D and 3D nozzle. some times your modeling is correct but your input data (e.g P out)is not correct. you can not use laminar model. your flow is turbulence.use boundary layer near your wall and you can use spallarat-almaras and K-epsilon and may be flow pressure in end of nozzle is smaller than atmosferic pressure . if your problem not solved mail me

Thank you very much Nasser. I put a Bounbary Condition on the wall and a lower pressure outlet (Pout=0,2bar) and it worked well with the S-A model. Regards Jeremie

[abdul Sami]

please can any one answer
why static pressure decrease in divergent section of nozzle and why total pressure and temperature remain constant througout the nozzle plz plz plz can any answer

[mrenergy]

Hi Sami,

it is basic science ...

total pressure and temperature remain constant throughout the nozzle ...

because they are the total energy ... they are constants unless shock wave occurs in the diverging part (supersonic NOZZLE)... or the nozzle is frictional


the static pressure increases in the converging section if the Mach number at throat became unity and the flow in the converging zone became supersonic ...
for supersonic flow ... the definitions of nozzle and diffuser are reversed ... according to the property relations for supersonic flow ...
and this is the reason for the name (converging - diverging NOZZLE)

Mamdouh

[abdul Sami]

thanks alot dear

[abdul Sami]

Plz tell me the terms, static pressure, total pressure, static temperature and total temperature with respect to convergent divergent nozzle I m so worried plzz help me I will be thankful i m not clear with these terms plz give detail answer

[mrenergy]

Hi Sami,

just google it, you will get many sources of information.

I did now, this is one example ...

http://www.google.ca/url?sa=t&rct=j&...MJv1DkYUMhX6Mg

try ... may you get better information

GOOD LUCK

Mamdouh

[abdul Sami]

thank you so much mamdouh

[kabilan]

hi sir,
could you please help to calculate jet pressure ratio.
in fluent pressure inlet condition total gauge pressure as 20bar,
supersonic/init pressure as 19.5 bar, and outlet pr is 1 bar,
how to calculate jet pressure ratio?
and total temperature of my inlet condition?
thank you sir..

[kabilan]

excuse me sir,
if i want to analyse into still air how can i give b.c value at outlet?