How to locate the vortex eyes in a vector field without using the data cursor and find the circulation around the eye.

greetings of the day

I am unable to extract the velocity values around the vortex eye inside a closed contour, so a to get the circulation. Dose anyone know how to isolate the velocity contour containg the vortex eye and find the circulation it. Ihave a .mat file of the velocity vector feild. I have calculated the curl but the i think its for the whole vector feild not at the particular region of recirculation . heres my code;

clear all

close all

load('B00001_X0_70_AvgV.mat')

x=x1';

y=y1';

vy=vy';

figure

contour(x,y,vy,15,'linewidth',1,'linecolor','b')

hold on

sr=surf(x,y,vy);

sr.EdgeColor='none';

sr.FaceColor='interp';

sr.FaceAlpha=0.8;

% [c,h]=contourf(x,y,vy,[0,-30.46],'linewidth',2);

contour(x,y,vy,[0,-30.46],'linewidth',1,'linecolor','k');

qv=quiver(x,y,vx',vy,'Color','k');

qv.LineWidth=2;

qv.AutoScaleFactor=1.5;

grid off

figure

surf(x,y,curl(vx',vy))

view(2)

% [curlx,curly,cav]=curl(x,y,vy);

%%It would be of great help if i can get some leads on it.

thanks

[raj sekhar]

i need to find the recirculation inside the contours defined by black lines. i have also attached the .mat file.

Thankyou for any help

raj

Answer 1

[darova]

You want to find velocities inbetween [0,-30.46]. So just select appropriate indices:

idx = -30.46 < vy & vy <= 0;
vy1 = vy;
vy1(~idx) = nan;
surf(x,y,vy1)

Maybe interpolation will be needed

x2 = linspace(min(x),max(x),100);
y2 = linspace(min(y),max(y),100);
[X2,Y2] = meshgrid(x2,y2);
vy2 = interp2(x,y,vy,X2,Y2);
idx = -30.46 < vy2 & vy2 <= 0;
vy2(~idx) = nan;
surf(X2,Y2,vy2)

[raj sekhar]

i am a beginnner in matlab and was stuck with his for a week, thank you so much @darova, this is perfect i have tried another method in the mean time : finding the local maxima in the flow feild which will give me the location of the eye and now about to find the circulation around it by defining an area around the eye. Well i will also use the code u have written for cross validation. I hope u dont mind if i stay in touch.

[darova]

YOu are welcome! Please accept the answer if it helped

[Ashfaq Ahmed]

hi @raj sekhar could you kindly let me know how did you find the location of the center of the vortex using the local maxima method? I am stack at the similar problem and it would be a great help if you kindly share your ideas.