Attractive internal wave patterns

This paper gives background information for the fluid dynamics video on internal wave motion in a trapezoidal tank.Comment: 2 pg, movie at two resolutions _low(Low-resolution) and _hr(High-resolution

Attractive internal wave patterns

This paper gives background information for the fluid dynamics video on internal wave motion in a trapezoidal tank.Comment: 2 pg, movie at two resolutions _low(Low-resolution) and _hr(High-resolution

Three-dimensional advective--diffusive boundary layers in open channels with parallel and inclined walls

We study the steady laminar advective transport of a diffusive passive scalar released at the base of narrow three-dimensional longitudinal open channels with non-absorbing side walls and rectangular or truncated-wedge-shaped cross-sections. The scalar field in the advective--diffusive boundary layer at the base of the channels is fundamentally three-dimensional in the general case, owing to a three-dimensional velocity field and differing boundary conditions at the side walls. We utilise three-dimensional numerical simulations and asymptotic analysis to understand how this inherent three-dimensionality influences the advective-diffusive transport as described by the normalised average flux, the Sherwood $Sh$ or Nusselt numbers for mass or heat transfer, respectively. We show that $Sh$ is well approximated by an appropriately formulated two-dimensional calculation, even when the boundary layer structure is itself far from two-dimensional. This important result can significantly simplify the modelling of many laminar advection--diffusion scalar transfer problems: the cleaning or decontamination of confined channels, or transport processes in chemical or biological microfluidic devices

Stratified inclined duct: direct numerical simulations

The stratified inclined duct (SID) experiment consists of a zero-net-volume exchange flow in a long tilted rectangular duct, which allows the study of realistic stratified shear flows with sustained internal forcing. We present the first three-dimensional direct numerical simulations (DNS) of SID to explore the transitions between increasingly turbulent flow regimes first described by Meyer \& Linden (\textit{J. Fluid Mech.} \textbf{753}, 242-253, 2014). We develop a numerical set-up that faithfully reproduces the experiments and sustains the flow for arbitrarily long times at minimal computational cost. We recover the four qualitative flow regimes found experimentally in the same regions of parameter space: laminar flow, waves, intermittent turbulence, and fully-developed turbulence. We find good qualitative and quantitative agreement between DNS and experiments and highlight the added value of DNS to complement experimental diagnostics and increase our understanding of the transition to turbulence, both temporally (laminar/turbulent cycles) and parametrically (as the tilt angle of the duct and the Reynolds number are increased). These results demonstrate that numerical studies of SID -- and deeper integration between simulations and experiments -- have the potential to lead to a better understanding of stratified turbulence in environmental flows

Editorial : Special issue on the 13th international workshop on the physics of compressible turbulent mixing

The study of compressible turbulent mixing associated with Richtmyer-Meshkov (RM), Rayleigh-Taylor (RT), and Kelvin-Helmholtz (KH) instabilities is motivated by diverse applications in science and engineering, including supersonic combustion, detonation, instability of collapsing gas bubbles, stratified flows in geophysical applications, chemical engineering, inertial confinement fusion (ICF), supernovae, and molecular clouds. Further, the interaction of shock waves with materials is also of interest in biomedical applications, such as fragmentation of cancer cells during shockwave chemotherapy and cavitation damage to human tissues during lithotripsy. In many of these applications, the Reynolds number is very high and the instabilities rapidly lead to turbulent mixing. In the case of ICF, which is regarded as a promising approach to controlled thermonuclear fusion: (1) these instabilities lead to the growth of perturbations on the interfaces within the capsules; (2) perturbations grow into the nonlinear regime by mode coupling and eventually cause mixing of materials; and (3) material mixing inhibits thermonuclear burning of the fuel

Accuracy of PECARN, CATCH, and CHALICE head injury decision rules in children: a prospective cohort study

© 2017 Elsevier Ltd Background Clinical decision rules can help to determine the need for CT imaging in children with head injuries. We aimed to validate three clinical decision rules (PECARN, CATCH, and CHALICE) in a large sample of children. Methods In this prospective observational study, we included children and adolescents (age

Variability of outcome measures in trials of intravenous therapy in acute severe paediatric asthma: a systematic review

Objective To determine the variability of primary and secondary outcomes used in trials of intravenous bronchodilators in children with acute severe paediatric asthma. Methods Systematic search of MEDLINE, EMBASE, Cochrane CENTRAL and the WHO International Clinical Trials Registry Platform for randomised trials in children (less than18 years) with acute severe paediatric asthma comparing intravenous bronchodilator therapy to another treatment. Initial search was performed on 7 January 2016 with an updated search performed on 6 September 2018. Primary and secondary outcomes were collated. Results We identified 35 published papers and four registered study protocols. 56 primary outcomes were found, the most common being a clinical asthma score (23/56; 41%). Other identified primary outcomes included bedside tests of respiratory function (11/56; 20%) and measures of length of stay (9/56; 16%). There were a total of 60 different secondary outcomes, the most common were various length of stay measures (24/60; 40%) and adverse events (11/60; 18%). Conclusion Studies comparing intravenous treatment modalities for children with acute severe paediatric asthma exhibit great variation in the type, number and timing of outcome measures used. There are no patient or family-specific outcomes reported. There is a need to develop international consensus