I was reading an article on the impact of jet in vanes. In this article I found that the net torque on the unsymmetrical or radially curved vanes is non zero. But, my question is that, why the torque on the symmetrical curved vane, when jet impinges tangentially at one end, is zero. My thoughts: As the force on the symmetrical vane, for the case described above, is in the horizontal direction only and the net force in vertical direction will be zero, if no losses are considered. Hence, the line of action of horizontal force is finite distance apart from the axis of the vane. Therefore, net troque must be finite. Note: this picture is only meant to define the sense of horizontal and vertical directions only and the axis of the vane and not the other terms which can vary according to the user.
A symetrical blade imparts the torque to the shaft with no turning force beween its ends.
However a non-symetrical blade will have an imbalance beween the torque one half compared to the other - which can cause one bearing to fail earlier for example or slight bending of the shaft causing clearance issues...