Isolate PVC with the Q-citerion

velkon · July 25, 2022, 09:24

Hi!
I am trying to isolate a precessing vortex core with the Q criterion. However because there are a lot of other structures visible when imposing a certain Q value, I can not see the PVC properly. Does anybody know a method where you can isolate the 3D PVC with the Q-criterion.

Kind regards,

sbaffini · July 27, 2022, 05:18

The stupid question first: does your velocity field suggest that a PVC is actually present?

Second, have you tried with different Q values?

I only worked on a single geometry with multiple swirl ratios, but I was able to visualize it both with the Q and lambda criterions.

velkon · July 27, 2022, 05:21

Quote:

Originally Posted by sbaffini

The stupid question first: does your velocity field suggest that a PVC is actually present?

Second, have you tried with different Q values?

I only worked on a single geometry with multiple swirl ratios, but I was able to visualize it both with the Q and lambda criterions.

Hi Sbaffini,
Thank you for your response. Yes from POD and experimental results it is clear that a PVC is present in the flow. Furthermore I can see the PVC with the Q criterion when imposing different values. However a lot of other structures are still also present making it hard to see it.

Do you perhaps know how to isolate the PVC from those other structures?

sbaffini · July 27, 2022, 05:55

Quote:

Originally Posted by velkon

Hi Sbaffini,
Thank you for your response. Yes from POD and experimental results it is clear that a PVC is present in the flow. Furthermore I can see the PVC with the Q criterion when imposing different values. However a lot of other structures are still also present making it hard to see it.

Do you perhaps know how to isolate the PVC from those other structures?

To isolate the PVC in general, POD is indeed a good approach, but for the Q criterion I don't know of any general technique to isolate specific structures. Also, if you already tried changing value of the Q isosurface, then you probably already tested the meaningful range of possible values, meaning that no way exists to isolate the PVC with the Q criterion.

What solver/visualizer are you using? How is your Q defined? Is it possible that it is coded wrong?

July 25, 2022, 09:24	Isolate PVC with the Q-citerion	#1
velkon New Member velkon123 Join Date: Jan 2020 Posts: 14 Rep Power: 8	Hi! I am trying to isolate a precessing vortex core with the Q criterion. However because there are a lot of other structures visible when imposing a certain Q value, I can not see the PVC properly. Does anybody know a method where you can isolate the 3D PVC with the Q-criterion. Kind regards, Last edited by velkon; July 25, 2022 at 10:57.

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July 27, 2022, 05:18		#2
sbaffini Senior Member Paolo Lampitella Join Date: Mar 2009 Location: Italy Posts: 2,213 Blog Entries: 29 Rep Power: 41	The stupid question first: does your velocity field suggest that a PVC is actually present? Second, have you tried with different Q values? I only worked on a single geometry with multiple swirl ratios, but I was able to visualize it both with the Q and lambda criterions.