To plot Cm vs azimuthal angle
 

I am working on 2D 3 blade VAWT simulation. I did the simulation in fluent for specific tsr. But i can't plot Cm vs azimuthal graph!!!! In xy plot from new iso surface i select the circular interface as x co-ordinate. But when i select it with curve length and Cm history file it says, "Can not plot curve length along x co-ordinate". But with direction vector it shows only position. Pls, someone help me to solve this................:(