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April 4, 2022, 02:22
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Confusion about velocity behavior in nozzle
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#1 |
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Member
Syed Wajeeh
Join Date: Mar 2022
Posts: 56
Rep Power: 4  |
Hello all, I am simulating supersonic flow in a bell nozzle and the problem I am facing is that the velocity starts decreasing after a certain length in the diverging section both for inviscid and viscid models. I am unable to grasp the reason behind it as I and my instructor both think that it should be constant if not increasing but should not decrease. I am attaching the screen shot of what I am saying. It will be a great favor if some one can help me in this regard.
Pressure Inlet = 5.099 MPa Pressure Outlet = 101325 Pa Models = Inviscid and k-w SST. comparison.JPG Density.JPG Temp.JPG Inv Velo.jpg viscid velocity.jpg |
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April 4, 2022, 04:37
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#2 |
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Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,675
Rep Power: 66 |
You're plotting centerline properties in a (2D?) 3D nozzle.
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April 4, 2022, 05:29
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#3 |
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Member
Syed Wajeeh
Join Date: Mar 2022
Posts: 56
Rep Power: 4 |
Yes, these are the graphs for center line velocity of a 2D planar nozzle.
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April 4, 2022, 08:31
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#4 |
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Senior Member
Matt
Join Date: Aug 2014
Posts: 947
Rep Power: 17 |
What does your mesh look like?
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April 4, 2022, 09:00
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#5 |
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Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,675
Rep Power: 66 |
No I'm saying you're looking at centerline properties in a real nozzle and thinking these are somehow equivalent to 1D isentropic flow
Welcome to the real-er world. |
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April 4, 2022, 09:06
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#6 |
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Member
Syed Wajeeh
Join Date: Mar 2022
Posts: 56
Rep Power: 4 |
I agree with you. But what I am asking is that for k-w SST, shouldn't it be increasing in the center in accordance with boundary layer flow development ? No issues if it is not behaving well for inviscid.
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April 6, 2022, 06:33
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#8 |
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Senior Member
Lorenzo Galieti
Join Date: Mar 2018
Posts: 373
Rep Power: 12 |
This to me is because you are not putting straight sections before and after the converging and diverging sections. For the first one, what happens is that you send undeveloped flow in the nozzle, for the second one, I have the feeling the pressure outlet interacts in a somehow weird way with the flow. You should not draw conclusions on the results near the boundary conditions
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April 6, 2022, 06:36
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#9 |
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Member
Syed Wajeeh
Join Date: Mar 2022
Posts: 56
Rep Power: 4 |
LoGal thanks mate. Cheers
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April 6, 2022, 07:31
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#10 |
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Senior Member
Lorenzo Galieti
Join Date: Mar 2018
Posts: 373
Rep Power: 12 |
just extend both ends of the nozzle quite a lot with straight sections ( 6-7 Diameters length) and redo the simulation. I believe it should improve the result
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April 6, 2022, 09:11
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#11 |
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Member
Syed Wajeeh
Join Date: Mar 2022
Posts: 56
Rep Power: 4 |
LoGal, will do. Thanks once gain
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