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super/sub sonic flows in laval nozzle

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Old   June 24, 2005, 06:21
Default super/sub sonic flows in laval nozzle
  #1
Kalyan
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I am currently working on supersonic flows and mass flow rates in Convergent-Divergent nozzle with StarCD 3.24. I am encountering some problems.

My nozzle is of dimensions

inlet dia : 9mm Outlet dia : 9mm throat dia : 3 mm throat length : 1mm total nozzle length :51mm

I am a beginner in Starcd and in Fluid dynamics stuff.

My design is a simple 2-d model (two conical sections meeting at the throat) with around 3000 elements.

boundaries are

pressure : 2 bar- 20 bar [ at one end of the nozzle]

pressure : 1 bar (constant all the time) [at another end of the nozzle]

rest of the cells as wall and i tried with symmetry BCīs too.

i have kept the density as a function dependent on temperature and pressure f(T,P) and viscosity as inviscid flow.

i have run with SIMPLE solver and a residual tolerance of 10e-5

As far as(from theory) i know that the mass flow rate should not increase after a certain pressure (after we reach mach 1).

but i see that from 2 bar - 20 bar the mass flow rate keeps on increasing.

i use the commands getc all dens integrate cset to get the mass flow rate

is there any problem with my model? can you please help me, why i cannot see the mass flow rate constant ...

can you please suggest me on the model, any help would be great

thanking you Kalyan Yalamanchili
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Old   June 24, 2005, 10:05
Default Re: super/sub sonic flows in laval nozzle
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Pauli
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If I understand your post, you're holding the downstream pressure constant & raising the upstream pressure.

I'm a bit rusty on supersonic flow. But I believe mass flow rate will continue to rise even after the nozzle chokes (Mach number = 1). I believe this is due to the increase in upstream density. Now if you hold the upstream pressure constant & continue to lower the downstream pressure, then mass flow rate will hit a limit at some pressure ratio. I don't remember the exact value.
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Old   June 24, 2005, 10:28
Default Re: super/sub sonic flows in laval nozzle
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kalyan yalamanchili
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thanx Pauli

i know that when the pressure is constant at the inlet and the pressure at the outlet is decreasing there will a choked flow...

are you sure that the inverse isīt true ...?

please confirm this .... if you have any links concerning this please do post them

thanx once again kalyan
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Old   June 24, 2005, 11:04
Default Re: super/sub sonic flows in laval nozzle
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Pauli
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Reference any text book on compressible flow or gas dynamics.
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Old   August 17, 2005, 17:58
Default Re: super/sub sonic flows in laval nozzle
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al
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try "nozzle" from http://www.aerorocket.com/products/products.html
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