Dr Dan Lucas

Layer formation and transition to turbulence in horizontally shearing stably stratified flows

Layers in stratified flows are regions of relatively well-mixed fluid separated by sharp gradients of temperature or density. They are commonly observed to arise spontaneously and are important in regulating the transport of heat, mass and nutrients in the ocean. Unfortunately there are limited theoretical descriptions of their origins and maintenance. In this talk we survey several new results for turbulent flows driven by a shear which is perpendicular to a stable stratification. First we show how in a body forced system layer formation can be associated to a stratified linear instability via nonlinear unstable steady solutions. Next we explore the differences when we instead drive the flow by moving boundaries in a plane Couette configuration. Here we find layers confined near the walls which are seemingly disconnected from any linear mechanism. However the layer scale provides insight into the way turbulence is shut-off when stratification becomes very large.