University of Western Ontario
London, Ontario, Canada
Using a spectral (fourier) method, we present numerical simulations of the evolution of finite-amplitude, two-dimensional disturbances to a $\tanh^{3}y$ mixing layer. This particular flow has three neutral modes, each of which has a strong singularity at the critical layer, and we examine the nonlinear interaction of these modes, finding that the behaviour is very different from that of the more usual $\tanh^{3}y$ mixing layer.