Unstable patterns in partly vegetated channels

Unstable patterns are identified in the results of numerical simulations of two cases of partly vegetated open channels, at the free unobstructed how side of the shear layer that separates the unobstructed channel from the vegetated zones. A time-dependent pattern was identified in a rectangular open channel compound with a vegetated bank, and cellular structure was found in a wide rectangular open channel spanning over a vegetated thin layer at the channel bed. Distinction between three modes of algebraic stress models: a prompt algebraic stress model, a delayed algebraic stress model, and an algebraic stress model with longitudinal vorticity sources relaxation, and the modeling of time-dependent turbulence is made, and discussed in the present context.