Global singularity-free solution of the Iordanskii force problem
  We present a derivation of the transverse force acting on a hydrodynamic vortex in the presence of an incoming sound wave from a global solution of the scattering problem, using the method of matched asymptotic expansions. The solution presented includes a detailed treatment of the interaction of the incident wave with the vortex core, and is free from the singularities in the momentum exchange between vortex and sound wave which have led to contradictory results for the value of the transverse force in the literature. 
Markus Flaig and Uwe R. Fischer