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tomasz.kura
Posts: 2
Registered: ‎10-26-2013

Compressible air flow in converging-diverging nozzle

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11-16-2013 02:19 AM

Hello!

 

I'm trying to analyse compressible air flow through c-d nozzle.I want to get Mach number equal 1 at the throat, and then make the air sonic. Due to theoretical formulas, to get desired Mach number at the end of it, we just need to know critical mass flow rate through the throat and 'end area to throat area ratio'. I've tried some combinations, but all the time I get wrong (smaller) Mach number.

 

For example for throat radius of 15 [mm], to get at the end 2,5 [Ma] radius for the final area should be 24,36 [mm], and mass flow rate: 0,6388 [kg/s]. Total temperature is 500 [K].

 

I've set variable condition for air, and tried many turbulence models, but all the time I can't get more, than 2,3 [Ma] at the end. What might be the explanation? All the time it's approximately 0,2 Ma less than theoretically.

 

 

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wildej
Posts: 781
Registered: ‎08-25-2011

Re: Compressible air flow in converging-diverging nozzle

11-18-2013 01:04 AM in reply to: tomasz.kura

Hi Tomasz,

 

Assuming your model is set up correctly with Mass Flow (or Total Pressure) and Total Temp upstream and unknown downstream you should be OK. Advection Schemes 2 and 5 should be best for compressible flow. I would suggest you start with 5.

You do only have an 8% error, which is not bad - perhaps some mesh refinement might bring you closer.

 



Jon Wilde
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New Member
tomasz.kura
Posts: 2
Registered: ‎10-26-2013

Re: Compressible air flow in converging-diverging nozzle

11-18-2013 03:27 PM in reply to: wildej

Thank you for answer.

 

I've tried both advection schemes. And many mesh settings as well.Unfortunatelly still getting the same results. In addition I've wanted to make the simulation dscribed here:

 

http://wikihelp.autodesk.com/Simulation_CFD/enu/2013/Help/0407-Learning407/0807-Verifica807/0815-Com...

 

to check if I'm able to get similar results. But again, I had different ones. Is it possible to receive full configuration for that case? It would propably help me get good results as well in my analysis.

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