Converging-Diverging Channel

This chapter presents the effect of convergence and divergence of a channel simultaneously on flow stability. The large value of wall surface waviness has been considered to study its effect on the critical Reynolds number. The temporal and spatial structure of the small disturbances is analysed for the forward, reverse and asymmetric geometry of the convergent-divergent channel. The three mechanisms of the instabilities, exponential instability, ratchet growth in space and localized large transient growth in time, are discussed.