Please help me to solve this problem!

I have been asked to calculate vorticity of three velocity components u, v & w. I have attached .txt file for the same. As I knew curl does the same in MATLAB. Hence i tried these lines of code:

u=VarName1;

>> v=VarName2;

>> w =VarName3;

>> Ulin =linspace(min(u),max(u),33);

>> Vlin =linspace(min(v),max(v),33);

>> Wlin =linspace(min(w),max(w),33);

>> [U,V,W]=meshgrid(Ulin,Vlin,Wlin);

>> [CURLX, CURLY, CURLZ, CAV] = curl(U,V,W);

But when I type CURLX all are showing zero values...

Answer 1

[Jos (10584)]

Did you check the contents of each variable?

Answer 2

[Roger Stafford]

By the way you have defined U, V, and W, they must have a curl of identically zero. There can be no vorticity. That is because U = (max(u)-min(u)/32*x, V = (max(v)-min(v)/32*y, and W = (max(w)-min(w)/32*z, so all the partial derivatives that go to make up the curl must be zero: dU/dy = dU/dz = dV/x = dV/dz = dW/dx = dW/dy = 0.

[the cyclist]

As a way of confirming Roger's wise words, note that if you add some random noise to your vectors:

U = U + rand(33,33,33);
V = V + rand(33,33,33);
W = W + rand(33,33,33);

then you will see non-zero curl everywhere.

[Rizwana]

I have u ,v and w in data set which is varying in values. I cannot meshgrid it because iam running out of memory. Hence using linspace space command

[Roger Stafford]

You will need to use the 'curl' function in the form

 [curlx,curly,curlz] = curl(X,Y,Z,U,V,W);

unless your X, Y, and Z are unit-spaced (see the documention.) The X, Y, Z need to be monotonic and in a form as if produced by 'meshgrid' though the spacing can be variable. These represent positions in the field, while U, V, and W represent the corresponding x, y, and z components of the vector field at these positions.

If your points are so numerous that you are running out of memory, you will have to do the computation in small enough sections of the field that you don't run out of memory. However, be aware that since the curl of the field is also a vector field, it will occupy just as much memory as the three arrays U, V, and W do.