Mean effects of turbulence on elliptic instability in fluids

Elliptic instability in fluids is discussed in the context of the Lagrangian-averaged Navier-Stokes-alpha (LANS$-\alpha$) turbulence model. This model preserves the Craik-Criminale (CC) family of solutions consisting of a columnar eddy and a Kelvin wave. The LANS$-\alpha$ model is shown to preserve the elliptic instability for the inviscid case. However, the model shifts the critical stability angle. This shift increases (resp. decreases) the maximum growth rate for long (resp. short) waves. It also introduces a band of stable CC solutions for short waves.