Eddy Viscosity Ratio Plots - interpretation

Using SimScale
1

I am finally able to use ParaView well enough to get some images that match what my brain wants to see :wink:

I have used the link @LWhitson2 provided a while back which expalains EVR plots. This is the link.

First I would like someone to interpret these 3 EVR plots (the 2nd just adds LIC to see how well attached flow is) that I have made, as they stand, on their own.

I will supply more information about the mesh and sim parameters as needed.

I have my own interpretation, but that is from a very newbie perspective, so I donā€™t want to say much yet :wink:

I am concerned about how I would change the mesh to better allow my boundary layer to be precisely analyzed as the connected flow approaches the trailing edgeā€¦

Any EVR experts out there (@LWhitson2 :pray: ā€¦)

EVR_and_yPlus
EVR_and_yPlus1711Ɨ1080 201 KB

EVR_and_yPlus_LIC
EVR_and_yPlus_LIC1711Ɨ1080 274 KB

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EDIT: Funny, at the autoscale color range, it looks like the BL is resolved much better???
I was just assumed that the correct range to view was what the link used, another ass u me issue ???
EVR_and_yPlus_aytorange
EVR_and_yPlus_aytorange1711Ɨ1080 196 KB

2

Hi Dale!

If you have your values of the EVR it just indicates the laminar or turbulent regimes. Thatā€™s actually just an ā€œeasierā€ way to think about the physical part than directly prescribing Reynolds stresses or k or epsilon at the inlet (for the inlet we usually prescribe the turbulent intensity). What was your interpretation of the EVR?

Cheers,

Jousef

3

Yes, that is my impression so far but I was trying to follow the logic at that linkā€¦

They use a 30 EVR max on all the sample plots they show, I now think that is not a hard and fast rule, as you say, the actual magnitude of EVR will be based on the turbulence values use for the simulation.

I guess I would like to know, is the 30 EVR max a hard value for interpretation :question:

My turbulence initial values were: k-omega SST with k=0.00325 m^2/s^2 and omega=142.5 1/s ā€¦

4

Hey Dale!

For most turbulent cases the range is around 1e3 to 1e4 (shear layers, fully-developed duct flows etc.) but from what I have read is that usually at free-stream boundaries of most external flow the EVR is between 1 and 10. However you are correct here Dale that this ratio can be used to see where the mesh has to be resolved better. I would have to read this up again and do a small research - forgot the exact procedure on such cases to be honest :slight_smile:

By the way, for k and epsilon, have you considered this post from @1318980 (Darren): Defining Turbulent Boundary Conditions ?

Best,

Jousef

5

I am pretty sure if I looked at that last fall, when I decided to use dylans method for k and omega calcsā€¦
I will have a look again when my SimScaling gets less hectic :wink: