Geometry and a priori estimates for free boundary problems of the   Euler's equation
  In this paper we derive estimates to the free boundary problem for the Euler equation with surface tension, and without surface tension provided the Rayleigh-Taylor sign condition holds. We prove that as the surface tension tends to zero, when the Rayleigh-Taylor condition is satisfied, solutions converge to the Euler flow with zero surface tension. 
Jalal Shatah and Chongchun Zeng