Inviscid drops with internal circulation

Abstract

The shape of a moving inviscid axisymmetric drop is considered as a function of surface tension and of the intensity of the internal circulation. In a frame of reference moving with the drop, the drop is modelled as a region of diffused vorticity which is bounded by a vortex sheet, and is imbedded in streaming flow. First, an asymptotic analysis is performed for a slightly non-spherical drop whose circulation is very close to that required for the spherical shape. The results indicate that steady drop shapes may exist at all but a number of distinct values of the Weber number, the lowest two of which are 4.41 and 6.15. For highly deformed drops, the problem is formulated as an integral equation for the shape of the drop, and for the strength of the bounding vortex sheet. A numerical procedure is developed for solving this equation, and numerical calculations are performed for Weber numbers between 0 and 4.41. Limiting members in the computed family of solutions contain spherical drops, and inviscid bubbles with vanishing circulation. Computed new shapes include saucer-like shapes with a rounded main body and an elongated tip. The relationship between inviscid drops and drops moving at large Reynolds numbers is discussed.