130 research outputs found
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 or Nusselt numbers for mass
or heat transfer, respectively. We show that 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
Inclined gravity currents filling basins: The influence of Reynolds number on entrainment into gravity currents
In many important natural and industrial systems, gravity currents of dense fluid feed basins. Examples include lakes fed by dense rivers and auditoria supplied with cooled air by ventilation systems. As we will show, the entrainment into such buoyancy driven currents can be influenced by viscous forces. Little work, however, has examined this viscous influence and how entrainment varies with the Reynolds number, Re. Using the idea of an entrainment coefficient, E, we derive a mathematical expression for the rise of the front at the top of the dense fluid ponding in a basin, where the horizontal cross-sectional area of the basin varies linearly with depth. We compare this expression to experiments on gravity currents with source Reynolds numbers, Res , covering the broad range 100 < Res < 1500. The form of the observed frontal rises was well approximated by our theory. By fitting the observed frontal rises to the theoretical form with E as the free parameter, we find a linear trend for E(Res ) over the range 350 < Res < 1100, which is in the transition to turbulent flow. In the experiments, the entrainment coefficient, E, varied from 4 × 10−5 to 7 × 10−2. These observations show that viscous damping can be a dominant influence on gravity current entrainment in the laboratory and in geophysical flows in this transitional regime
Antenatal corticosteroids for accelerating fetal lung maturation for women at risk of preterm birth
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
Inclined gravity currents filling basins: The influence of Reynolds number on entrainment into gravity currents
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
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