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June 24, 2005, 07:21 |
super/sub sonic flows in laval nozzle
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#1 |
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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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June 24, 2005, 11:05 |
Re: super/sub sonic flows in laval nozzle
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#2 |
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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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June 24, 2005, 11:28 |
Re: super/sub sonic flows in laval nozzle
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#3 |
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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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June 24, 2005, 12:04 |
Re: super/sub sonic flows in laval nozzle
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#4 |
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Reference any text book on compressible flow or gas dynamics.
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August 17, 2005, 18:58 |
Re: super/sub sonic flows in laval nozzle
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#5 |
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try "nozzle" from http://www.aerorocket.com/products/products.html
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