CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   FLUENT (https://www.cfd-online.com/Forums/fluent/)
-   -   Rocket Nozzle problem (https://www.cfd-online.com/Forums/fluent/38755-rocket-nozzle-problem.html)

 Jeremie November 28, 2005 12:44

Rocket Nozzle problem

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

 nasser November 29, 2005 03:53

Re: Rocket Nozzle problem

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

 Jeremie November 29, 2005 10:10

Re: Rocket Nozzle problem

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 February 17, 2013 11:48

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 February 17, 2013 12:42

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 February 18, 2013 02:12

thanks alot dear

 abdul Sami February 18, 2013 04:06

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 February 18, 2013 05:57

Hi Sami,

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

I did now, this is one example ...

try ... may you get better information

GOOD LUCK

Mamdouh

 abdul Sami February 18, 2013 22:29

thank you so much mamdouh

 kabilan October 8, 2014 06:13

pressure ratio

hi sir,