In your description, Rizwana, you haven't made it clear what components of velocity the variables u, v, and w represent. Apparently you have cylindrical coordinates x, y, and z where y is the radial direction, z is the axial direction, and x is the angular direction. What is the correspondence between these latter three directions and u, v, and w? Which corresponds to which? (Note: It is inadvisable to use x and y for radius and angle notation, since these symbols are so commonly used for cartesian coordinates.)
You say "it is just axial direction of flow", but what does that mean? Are you (or your guide) saying that u, v, and w are constant in the axial direction? If so, it is still quite possible to have nonzero curl components in all three directions even with constant values along the z-direction.
It is important to realize that matlab's 'curl' function is valid only for cartesian coordinates. Here is what curl looks like in cylindrical coordinates according to one of my textbooks:
curl A = er*(1/r*dAz/dt-dAt/dz) + et*(dAr/dz-dAz/dr) ...
+ ez*(1/r*d(r*At)/dr-1/r*dAr/dt)
where r is the radius, t is the angle in radians, and z is the distance along the axial direction. Presumably what you called y is called r here, what you called x is called t here, and your z is this z. The vectors er, et, and ez are unit vectors in the r, t, and z directions and Ar, At, and Az are corresponding components of the field vector A.
You described your u, v, and w quantities as being 220-element column vectors. It is to be hoped that these actually represent some kind of two-dimensional grid. Otherwise you will never be able to compute all the partial derivatives you need.
