  In this work, we present general solutions for closely spaced co-rotating
helical vortices using a filament approach. For these vortex structures,
helical symmetry is broken, but solutions maintain a form of spatial
periodicity. We show there exists a moving frame where vortex elements move
along the structure without distorting it. These solutions can be used to
characterize the evolution of the twin-tip vortices produced in the wake of a
tip-splitting rotor blade. The resulting wake has a dual nature. Locally, the
structure behaves much like an helical pair aligned with the locally tangent
flow. However, as we move away from the vortex structure the induced flow is
reminiscent of an 'equivalent' helical vortex with thicker core.
