Lee waves in a stratified flow Part 3. Semi-elliptical obstacle

Lee waves from a sphere in a stratified flow

Flow of foam past an elliptical obstacle.

To investigate the link between discrete small-scale and continuous large scale mechanical properties of a foam, we observe its two-dimensional flow in a channel, around an elliptical obstacle. We measure the drag, lift, and torque acting on the ellipse versus the angle between its major axis and the flow direction. The drag increases with the spanwise dimension, in marked contrast with a squar...

Stratified Kolmogorov flow . Part 2

Forced stratified flows are shown to suffer two types of linear long-wave instability: a ‘viscous’ instability which is related to the classical instability of Kolmogorov flow, and a ‘conductive instability’, with the form of a large-scale, negative thermal diffusion. The nonlinear dynamics of both instabilities is explored with weakly nonlinear theory and numerical computations. The introducti...

Lee Waves and Mountain Waves ∗

Buoyancy perturbations develop when stably stratified air ascends a mountain barrier. These perturbations often trigger disturbances that propagate away from the mountain as gravity (or buoyancy) waves. Gravity waves triggered by the flow over a mountain are referred to as mountain waves or lee waves. Mountain waves sometimes reveal their presence through dramatic cloud formations, such as smoo...

The Dissipation of Trapped Lee Waves. Part I: Leakage of Inviscid Waves

Leaky trapped mountain lee waves are investigated by examining the structure of individual linear modes in multilayer atmospheres. When the static stability and cross-mountain wind speed are constant in the topmost unbounded layer, modes that decay exponentially downstream also grow exponentially with height. This growth with height occurs because packets containing relatively large amplitude w...