## Search

Now showing items 1-10 of 27

#### Disruption of SSP/VWI states by a stable stratification

(Cambridge University PressJournal of Fluid Mechanics, 2015-11-06)

We identify ‘minimal seeds’ for turbulence, i.e. initial conditions of the smallest possible total perturbation energy density Ec that trigger turbulence from the laminar state, in stratified plane Couette flow, the flow ...

#### Instabilities of interacting vortex rings generated by an oscillating disk

(American Physical SocietyPhysical Review E, 2016-09-14)

We propose a natural model to probe in a controlled fashion the instability of interacting vortex rings shed from the edge of an oblate spheroid disk of major diameter $\textit{c}$, undergoing oscillations of frequency ...

#### Multiple instability of layered stratifed plane Couette flow

(Cambridge University PressJournal of Fluid Mechanics, 2017-02-25)

We present the linear stability properties and nonlinear evolution of two-dimensional plane Couette flow for a statically stable Boussinesq three-layer fluid of total depth 2$h$ between two horizontal plates driven at ...

#### Nonlinear evolution of linear optimal perturbations of strongly stratified shear layers

(Cambridge University PressJournal of Fluid Mechanics, 2017-08-25)

The Miles-Howard theorem states that a necessary condition for normal-mode instability in parallel, inviscid, steady stratified shear flows is that the minimum gradient Richardson number, $Ri_{g,min}$, is less than 1/4 ...

#### Testing linear marginal stability in stratified shear layers

We use two-dimensional direct numerical simulations of Boussinesq stratified shear layers to investigate the influence of the minimum gradient Richardson number Rim on the early time evolution of Kelvin–Helmholtz instability ...

#### The structure and origin of confined Holmboe waves

(Cambridge University PressJournal of Fluid Mechanics, 2018-08-10)

Finite-amplitude manifestations of stratified shear flow instabilities and their spatio-temporal coherent structures are believed to play an important role in turbulent geophysical flows. Such shear flows commonly have ...

#### Dependence on aspect ratio of symmetry breaking for oscillating foils: implications for flapping flight

(Cambridge University PressJournal of Fluid Mechanics, 2015-12-07)

Using two-dimensional direct numerical simulations, we investigate the flow in a fluid of kinematic viscosity ν and density ρ around elliptical foils of density ρ_s with major axis c and minor axis b for three different ...

#### A new method for isolating turbulent states in transitional stratified plane Couette flow

(Cambridge University PressJournal of Fluid Mechanics, 2016-10-26)

We present a new adaptive control strategy to isolate and stabilize turbulent states in transitional, stably stratified plane Couette flow in which the gravitational acceleration (non-dimensionalized as the bulk Richardson ...

#### Robust identification of dynamically distinct regions in stratified turbulence

(Cambridge University PressJournal of Fluid Mechanics, 2016-10-18)

We present a new robust method for identifying three dynamically distinct regions in a stratified turbulent flow, which we characterise as quiescent flow, intermittent layers and turbulent patches. The method uses the ...

#### Nonlinear effects in buoyancy-driven variable-density turbulence

(Cambridge University PressJournal of Fluid Mechanics, 2017-01-01)

We consider the time dependence of a hierarchy of scaled L²ᵐ-norms D_m,ω and D_m,θ of the vorticity ω =∇ x u and the density gradient ∇θ, where θ = log.(ρ*/ ρ*₀), in a buoyancy-driven turbulent flow as simulated by Livescu ...