Dynamics of vorticity fronts

Abstract

Vorticity fronts can form in a shear flow as the result of fast patches of fluid catching up with slower ones. This process and its consequences are studied in an inviscid two-dimensional model consisting of piecewise uniform-vorticity layers. Calculations using the method of contour dynamics for ‘intrusive’ initial states indicate that the leading edge of the front evolves into a robust structure whose propagation speed can be accounted for by a simple shock-joining theory. Behind the leading edge several different effects can occur depending upon the relative amplitude of the intrusion. These effects include lee-wave generation with possible wave breaking and folding of the front. A critical value of the frontal slope, above which wave breaking occurs, is suggested.