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December 4, 2016, 20:15 |
Diffuser simulation in Fluent
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#1 |
New Member
Join Date: Dec 2016
Posts: 2
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Hi all,
I'm trying to simulate an annular diffuser (pre+dump diffuser, see pic) of a combustor. The simulation is in 2D axisymmetric. I have used several turbulence models including k-epsilon, k-omega and RSM. It seems to me that the predicted total pressure loss at the pre-diffuser outlet (i.e. from 1-2 in the pic) is significantly lower than the experimental value (about 50% lower). The y+ of the mesh is lower than 2.5 which I think should be okay and finer mesh didn't make any difference. I also used the inlet velocity profile obtained from the experiment as the inlet condition. What do you think could possibly be the reason? I 've also noticed that by increasing the inlet turbulent intensity, the total pressure loss could increase. If that's the case, what intensity is suitable with a Re=2*10^5 and inlet height=38.1mm. I initially set it to 4% but the predicted total pressure loss was too low. Thanks for your suggestions. Alice |
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December 5, 2016, 10:59 |
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#2 |
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Join Date: Oct 2015
Posts: 5
Rep Power: 11 |
Hi alicesun
You can check this link, https://goo.gl/rc8TY4 , as it says: " High-turbulence case: High-speed flow inside complex geometries like heat-exchangers and flow inside rotating machinery (turbines and compressors). Typically the turbulence intensity is between 5% and 20% " Also by checking both the Medium-turbulence &Low-turbulence cases, I think that annular diffuser of a combustor is considered as a High-turbulence case with turbulence intensity is between 5% and 20%. For a sensible change in the value of pressure loss, take the turbulence intensity by 10%, after that compare it with experimental value. |
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December 8, 2016, 06:26 |
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#3 |
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Hi Mohy,
Thanks a lot for the suggestion. As you said, I did increase the turbulence intensity to 10% and the total pressure loss increased too. However, in the experiment it is stated that the flow is a fully developed flow from an intake with a very long settling length, which is not the case of turbomachinery where flow comes from the OGV exit with some distortion. In such circumstances, do you think I=10% is still reasonable? As the equation for fully developed flow in your link says, I obtain an intensity around 4% for a Reynolds number of 2*10^5. Kind regards, Alice |
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Tags |
combustor, diffuser, fluent, total pressure drop |
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