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April 29, 2013, 07:32 |
Q-criterion
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#1 |
New Member
Carlo
Join Date: Apr 2013
Posts: 2
Rep Power: 0 |
Hi,
could you help me to create a Matlab script for visualization of vortex by Q-criterion? I have the gradient of velocity gained by DNS with software Channelflow. This file because of the construct for becomes 4-D double: 32x33x32x9, where 9 indicates le nine components of the gradient in every nodes. How can I write the script to display the vortex by the Q-criterion? Q = 0.5(Ω^2− S^2), where Ω=tr[ΩΩt ]^1/2and S=tr[SSt ]^1/2 with S = 1/2 (∇v + (∇v)t) and Ω= 1/2(∇v - (∇v)t) but how I use ∇v ? In Matlab, please. Thanks a lot |
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April 29, 2013, 12:16 |
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#2 |
Senior Member
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Let us suppose you have the following matrix:
x(nx,ny,nz): x coordinates of your grid y(nx,ny,nz): y coordinates of your grid z(nx,ny,nz): z coordinates of your grid dudx(nx,ny,nz): x-wise derivative of x-wise velocity component dudy(nx,ny,nz): y-wise derivative of x-wise velocity component . . . dwdz(nx,ny,nz): z-wise derivative of z-wise velocity component This is, more or less, how i would put it down in Matlab: %MATLAB CODE iso_q=100; %Pick your number here %Definition of Q q=-0.5*(dudx.^2+dvdy.^2+dwdz.^2)-dudy.*dvdx-dudz.*dwdx-dvdz.*dwdy; %Plotting a Q isosurface, Q=iso_q figure() p=patch(isosurface(x,y,z,q,iso_q)); set(p,'FaceColor','red','EdgeColor','none'); daspect([1,1,1]) axis tight ax = -1; ay = 1; az = 1; view([ax,ay,az]); camroll(240) camlight lighting gouraud %END OF MATLAB CODE hope it works |
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April 30, 2013, 03:19 |
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#3 |
New Member
Carlo
Join Date: Apr 2013
Posts: 2
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Thanks a lot...
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April 30, 2013, 14:32 |
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#5 |
Senior Member
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Dear Far,
i'm glad you appreciate my contributions. I admit that is now a long time i'm thinking about putting all this stuff together in some place that i already identified as a cfd-online blog... However, as you may imagine, time is never enough as all the material would require some modifications or testing before being directly posted for the general use. In contrast, posting specific answers once in a while is more easy and directly useful for the one who asked. Nonetheless, as my working group was also considering this opportunity to "share stuff", i promise i will now seriously consider posting on a blog. |
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July 11, 2018, 14:48 |
uits for Q-criterion
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#10 |
New Member
Josh
Join Date: Jul 2018
Posts: 1
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I have a simple question what units are used for q-criterion
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July 11, 2018, 15:55 |
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#11 | |
Senior Member
Santiago Lopez Castano
Join Date: Nov 2012
Posts: 354
Rep Power: 15 |
Quote:
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July 11, 2018, 15:58 |
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#12 |
Senior Member
Santiago Lopez Castano
Join Date: Nov 2012
Posts: 354
Rep Power: 15 |
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