The
Environmental Fluid Mechanics Research Group aims
to understand the fundamental dynamics of flow and
transport in environmental system and,
consequently, to improve our ability to model and
monitor these systems. Environmental Fluid
Mechanics have a wide range of impacts on many
environmental problems related to climate change,
air quality, hydrology, ecology, and sustainable
development, to name a few.
From
the effect of millimeter-scale turbulence on water
condensation around submicron particles in clouds
to the global-scale atmospheric and oceanic
currents that control the climate and the weather
on earth, the flows of environmental fluids
interact with other physical, chemical, and
biological processes to shape the world around us.
While we try, and sometimes succeed, in developing
accurate mathematical models for these processes
based on first principles, the
strong interaction of the various processes and
scales make it impossible to have a "model of
everything" that can capture all the complexities of
our environment. In addition, the engineering of
manmade systems and their interaction with the
natural systems further complicate the task.
The
alternative approach that is used today is to try
too isolate one or a set of processes and study
them, analytically numerically or experimentally,
while parameterizing their interaction with the
other, neglected, processes. Global climate models
for examples parameterize the effect of geophysical
turbulence; air quality models often parameterize
the physical and chemical interactions with the
earth surface, and cloud models parameterize all the
small scale physico-chemical processes. These
parameterizations are of course themselves simple
models for the processes we elect not to model in
detail.
In
the Environmental Fluid Mechanics Research Group at
Princeton, we seek to develop models for the
dynamics of geophysical flow and transport at scales
that are relevant to environmental problems, i.e.
from millimeters up to a few kilometers. For each
problem, we seek the best combination of analytical,
numerical, and experimental tools to find the
appropriate solutions.
On
the analytical side, we use simplified forms of the
governing equations (the Navier-Stokes equations)
and similarity theories (such as the Monin-Obukhov
Similarity Theory) to focus on the most important
dynamics in environmental flows.
On
the numerical side, we mostly use the
large eddy simulation technique (LES),
which solves only for the largest
turbulent scales, to simulate
environmental flows and transport in
complex domains, (see figure to the
right). We are also very actively
involved in improving the
parameterization of unresolved
turbulence in LES and the
parameterizations, in coarser
geophysical models, of unresolved
physics such as surface variability (see
figure below), atmospheric boundary
layers , etc
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Contours
of the Smagorinsky coefficient (rough
indicator of the turbulence intensity)
around a building
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Velocity
deviation from its horizontal mean in an LES
over a roughness transition. We can discern
three zones, the internal boundary layer (IBL),
the zone of upstream plume(s), and the mixed
zone above the blending height
On
the experimental side, we use in-situ point sensors,
remote sensors, and distributed sensing networks to
measure the wide range of spatial and temporal
scales of atmospheric flows and their interaction
with the surface. The long-term aim of our efforts
is to combine experimental data and simulations and
to assimilate them them into integrated frameworks
to elucidate environmental dynamics and guide
environmental policy.
Met
station setup at roof of the
Engineering Quadrangle - Princeton
University
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Measuring surface fluxes using the
eddy covariance technique on the
plaine-morte (work with the EFLUM lab
at EPFL)
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Measuring
heat & momentum fluxes using
scintillometers on the roofs of EPFL
campus (work with the EFLUM lab at
EPFL)
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