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Flow reversal in the sliding mesh of a centrifugal fan

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Old   July 20, 2023, 14:26
Default Flow reversal in the sliding mesh of a centrifugal fan
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kartik khanna
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Hi all,

Can any of you please throw some light on the below results which I have got from the transient analysis of a 3D centrifugal pump (sliding mesh)

So, basically I have created 2 cases which are as follows:
1. Centrifugal fan rotating CCW at 1500 rpm at 24pa Outlet static and 0pa total inlet.
2. Same fan rotating at 400 rpm CCW at 24pa Outlet static and 0pa total inlet.

Below are the plots of velocity vectors' plots obtained for the two results.

1. For 1500 rpm, the plots have been shown for 0.2175s, 3.51s and 6.05s. If you see the plots, you will notice that the flow is reversing back from the outlet back into the rotor and this reverse flow is increasing with time. What do you think the reason might be. I understand that the flow reversal is logical to happen in first few timesteps since the rotation of the rotor might create some negative pressure inside which is filled in by the flow reversal. But why is the flow reversal increasing over time?

2. For 400 rpm, below are the velocity plots at time steps 0.145s and 3.156s. Here also, the trend is same as 1500 rpm.

Can someone please let me know as to what the reason of this increasing flow reversal might be? I have tried running the cases at lower outlet static pressure of 3pa (just to make sure that the higher static pressure isn't causing the flow reversal). But the results have been the same. I can post the solver settings if that is imperative to explain what is happening.

Thanks and Regards
Attached Images
File Type: jpg 400rpm_0.145s.jpg (79.1 KB, 8 views)
File Type: jpg 400rpm_3.51s.jpg (97.8 KB, 8 views)
File Type: jpg 1500rpm_0.2175s.jpg (87.4 KB, 5 views)
File Type: jpg 1500rpm_3.51s.jpg (116.7 KB, 4 views)
File Type: jpg 1500rpm_6.0537s.jpg (87.1 KB, 4 views)
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centrifugal fan, cfd - post, reverse flow, sliding mesh, staticpressure

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