The stability of inviscid vortex streets of finite cored vortices

The stability of two-dimensional infinitesimal disturbances of the inviscid Karman vortex street of finite area vortices is reexamined. Numerical results are obtained for the growth rate and oscillation frequencies of disturbances of arbitrary subharmonic wavenumber and the stability boundaries are calculated. The stabilization of the pairing instability by finite area demonstrated by Staffman and Schatzman (1982) is confirmed and also Kida's (1982) result that this is not the most unstable disturbance when the area is finite. Contrary, however, to Kida's quantitative predictions, it is now found that finite area does not stabilize the street to infinitesimal two-dimensional disturbances of arbitrary wavelength and that it is always unstable except for one isolated value of the aspect ratio which depends upon the size of the vortices.