70 research outputs found
DATIV - Remote enhancement of smart aerosol measurement system using Raspberry Pi based distributed sensors
Enclosed public spaces are the hotspots for airborne disease transmission. To measure and maintain indoor air quality in terms of airborne transmission, an open source, low cost and distributed array of Particulate Matter Sensors has been developed and named as Dynamic Aerosol Transport for Indoor Ventilation or DATIV system. This system can use multiple Particulate Matter Sensors (PMS) simultaneously and can be remotely controlled using a Raspberry Pie based operating system. The data acquisition system can be easily operated using the GUI within any common browser installed on a remote device such as a PC or Smartphone with corresponding IP address. The software architecture and validation measurements are presented together with possible future developments
Taylor-Couette turbulence at radius ratio : scaling, flow structures and plumes
Using high-resolution particle image velocimetry we measure velocity
profiles, the wind Reynolds number and characteristics of turbulent plumes in
Taylor-Couette flow for a radius ratio of 0.5 and Taylor number of up to
. The extracted angular velocity profiles follow a log-law more
closely than the azimuthal velocity profiles due to the strong curvature of
this setup. The scaling of the wind Reynolds number with the Taylor
number agrees with the theoretically predicted 3/7-scaling for the classical
turbulent regime, which is much more pronounced than for the well-explored
case, for which the ultimate regime sets in at much lower Ta. By
measuring at varying axial positions, roll structures are found for
counter-rotation while no clear coherent structures are seen for pure inner
cylinder rotation. In addition, turbulent plumes coming from the inner and
outer cylinder are investigated. For pure inner cylinder rotation, the plumes
in the radial velocity move away from the inner cylinder, while the plumes in
the azimuthal velocity mainly move away from the outer cylinder. For
counter-rotation, the mean radial flow in the roll structures strongly affects
the direction and intensity of the turbulent plumes. Furthermore, it is
experimentally confirmed that in regions where plumes are emitted, boundary
layer profiles with a logarithmic signature are created
An experimental study of regime transitions in a differentially heated baroclinic annulus with flat and sloping bottom topographies
A series of laboratory experiments has been carried out in a thermally driven
rotating annulus to study the onset of baroclinic instability, using horizontal
and uniformly sloping bottom topographies. Different wave flow regimes have
been identified and their phase boundaries -- expressed in terms of appropriate
non-dimensional parameters -- have been compared to the recent numerical
results of \citet{thomas_slope}. In the flat bottom case, the numerically
predicted alignment of the boundary between the axisymmetric and the regular
wave flow regime was found to be consistent with the experimental results.
However, once the sloping bottom end wall was introduced, the detected
behaviour was qualitatively different from that of the simulations. This
disagreement is thought to be the consequence of nonlinear wave-wave
interactions that could not be resolved in the framework of the numerical
study. This argument is supported by the observed development of interference
vacillation in the runs with sloping bottom, a mixed flow state in which
baroclinic wave modes exhibiting different drift rates and amplitudes can
co-exist
Benchmarking in a rotating annulus: a comparative experimental and numerical study of baroclinic wave dynamics
The differentially heated rotating annulus is a widely studied tabletop-size
laboratory model of the general mid-latitude atmospheric circulation. The two
most relevant factors of cyclogenesis, namely rotation and meridional
temperature gradient are quite well captured in this simple arrangement. The
radial temperature difference in the cylindrical tank and its rotation rate can
be set so that the isothermal surfaces in the bulk tilt, leading to the
formation of baroclinic waves. The signatures of these waves at the free water
surface have been analyzed via infrared thermography in a wide range of
rotation rates (keeping the radial temperature difference constant) and under
different initial conditions. In parallel to the laboratory experiments, five
groups of the MetStr\"om collaboration have conducted numerical simulations in
the same parameter regime using different approaches and solvers, and applying
different initial conditions and perturbations. The experimentally and
numerically obtained baroclinic wave patterns have been evaluated and compared
in terms of their dominant wave modes, spatio-temporal variance properties and
drift rates. Thus certain ``benchmarks'' have been created that can later be
used as test cases for atmospheric numerical model validation
Reference experiment on aerosol particle transport for dynamic situations
To study airborne transport of aerosol particles by mixed convection and dynamic situations within a closed room, the Cottbus Aerosol Particle Reference Experiment (CARE) was built and equipped, which includes thermal manikins and a spreader dummy. For various flow configurations (location of spreader, heating bodies, windows opened, air ventilation with and without air purification systems) flow visualisation was performed, particulate matter sensors (PMS) measured local particle concentrations, head-mounted camera systems counted particle concentrations of individuals and finally, large field of view Shake-The-Box Particle Tracking delivered velocity fields. The comprehensive experimental configuration of different measurement systems are discussed in terms of their aerosol transport properties and quantitative results, effective application and comparative efficiency explaining the flow dynamics. The findings from these experiments also provide information under which circumstances particularly high concentrations of aerosol particles can be found on which locations
Thermoelectric convection in a planar capacitor: theoretical studies and experiments in parabolic flights
International audienceNous avons étudié la convection thermoélectrique dans un condensateur plan placé dans un environnement de microgravité et dans des conditions terrestres avec une stratification thermique instable ou stable. L’analyse énergétique montre que dans le cas de stratification stable, la convection thermoélectrique est retardée alors que dans le cas de stratification thermique instable, elle est amplifiée par la poussée d’Archimède avant que cette dernière ne prenne le dessus et pilote la convection thermique naturelle. Une expérience réalisée lors des vols paraboliques illustre la formation de la convection thermoélectrique à la fin de la phase de microgravité
a comparative experimental and numerical study of baroclinic wave dynamics
The differentially heated rotating annulus is a widely studied tabletop-size
laboratory model of the general mid-latitude atmospheric circulation. The two
most relevant factors of cyclogenesis, namely rotation and meridional
temperature gradient are quite well captured in this simple arrangement. The
radial temperature difference in the cylindrical tank and its rotation rate
can be set so that the isothermal surfaces in the bulk tilt, leading to the
formation of baroclinic waves. The signatures of these waves at the free water
surface have been analyzed via infrared thermography in a wide range of
rotation rates (keeping the radial temperature difference constant) and under
different initial conditions. In parallel to the laboratory experiments, five
groups of the MetStröm collaboration have conducted numerical simulations in
the same parameter regime using different approaches and solvers, and applying
different initial conditions and perturbations. The experimentally and
numerically obtained baroclinic wave patterns have been evaluated and compared
in terms of their dominant wave modes, spatio-temporal variance properties and
drift rates. Thus certain “benchmarks” have been created that can later be
used as test cases for atmospheric numerical model validation
The state of the Martian climate
60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes
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