The sharp corner formation in 2d Euler dynamics of patches: infinite   double exponential rate of merging
  For the 2d Euler dynamics of patches, we investigate the convergence to the singular stationary solutions in the presence of a regular strain. It is proved that the rate of merging can be made double exponential for all time. 
Sergey A. Denisov
math.AP math-ph math.MP physics.flu-dyn