Seeing the organic curvature of some newer fans in turbofan engines, I'm curious if they use bell shaped lift distribution curves in their design, or something else all together.
The bell shaped lift distribution has been used on the Horten flying wings in order to reduce lift at the outer, rearward parts of the wing for stability and better controllability.
The fan blade of a jet engine has no need for a tailored reduction in lift towards the tips; instead it tries to maximize the thrust from the available area. The wavy shape is the result of a compromise which tries to sweep the outer, supersonic part of the blade aft and at the same time to minimize the torsion resulting from that sweep. Therefore, the blade is first swept forward and then aft.
RR Trent fan (picture source)