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Experimental and Numerical Studies of Stably Stratified Turbulent Boundary Layers

2009-11 Seed Grant

Owen Williams
Graduate student Owen Williams sits next to the thermally stable boundary layer tunnel at Princeton's Gas Dynamics Lab. In the background is the Particle Image Velocimetry (PIV) system consisting of a high speed camera and Ar-Ion laser

Princeton faculty from Civil and Environmental Engineering (CEE), Mechanical and Aerospace Engineering (MAE), and collaborators from the Geophysical Fluid Dynamics Laboratory (GFDL) and University of Maryland are using computer simulations and wind tunnel experiments to improve the representation of the atmospheric boundary layer in climate model simulations.

One of the major scientific challenges of this century is the critical need to improve measurements and modeling of environmental systems and how they interact with engineered systems, with the ultimate aims of:

  1. Enhancing the sustainability of engineered systems by reducing their environmental impacts.
  2. Mitigating the effect of global environmental change on these systems, the economy, and society.

To that end, significant research efforts are focusing on advancing our understanding of the dynamics of geophysical fluid flows.

Atmospheric dynamics are of special importance in view of the increasing observational data and climate model predictions strongly indicating that climate patterns are changing in response to increasing concentrations of anthropogenic greenhouse gases in the atmosphere.

However, current efforts to advance general circulation models, the main tool for studying climate dynamics, are hampered by major deficiencies in the models representing the small-scale, unresolved physical processes. Specifically, major efforts are needed to improve the representations of clouds and of the atmospheric boundary layer (ABL) in these models.

Here, Bou-Zeid and colleagues are working to improve understanding of the stably-stratified turbulent atmospheric boundary layer, observed during nighttime and over polar regions, in order to improve its parameterization in climate and weather models.

To date, laboratory experiments and a suite a numerical simulations ranging from Direct Numerical Simulations (grid size ~ 1 mm) to Single Column Model (SCM) simulations (grid size ~ several km) have yielded new insights into the dynamics of the stable ABL and the role of buoyancy in modulating its turbulence. The project has also led to the development of an improved simple parameterization of the stable ABL for GFDL’s SCM.

The work is intended to lead to enhanced predictive capabilities related to wind-energy and polar atmospheric chemistry. Bou-Zeid has received funding from the National Science Foundation to continue work initiated in this project. To learn more about this project, visit the Environmental Fluid Mechanics and Gas Dynamics Lab websites.

Educational Impacts

As part of this project, Bou-Zeid developed the course “Environmental Fluid Mechanics” (CEE 305) where final course projects focused on energy and the environment. Several students studied wind and temperature profiles in the stable ABL collected using a SODAR deployed at Forrestal campus as well as aircraft profiles, while others studied a range of topics including heat flux in walls, thermoregulation of elephants, and CO2 flux measurements over Princeton’s campus. The course presents aspects and applications of fluid dynamics and will increasingly serve as a bridge between CEE, MAE and Geosciences. The course “Boundary Layer Meteorology” (CEE/ GEO/ AOS 588) was heavily revised as part of the project.

At the graduate level, the Ph.D. dissertations of Owen Williams (MAE) and Stimit Shah (CEE) are significantly focused on stable turbulent boundary layers.

Summer intern Laszlo Szocs ’13 participated in the construction of the Particle Image Velocimetry (PIV) system required for velocity field measurements while Emily Moder ’13 conducted an analysis of the angle of turbulent coherent structures in thermally stable flows as well as the measurements of temperature variation across the boundary layer.

Other Outcomes

Since 2009, the project has fostered a series of yearly SEAS-AOS-GFDL workshops on “Fluid Dynamics & the Global Environment”, which aim to bridge the engineering, geosciences, and GFDL communities.

A proceedings paper titled “Turbulent Coherent Structures in a Thermally Stable Boundary Layer” was published from the presentation by Owen Williams at the Seventh International Symposium on Turbulence and Shear Flow Phenomena in Ottawa, July 2011.

Participating Departments

Collaborating Institution

Elie Bou-Zeid, Assistant Professor, Civil and Environmental Engineering

Robert W. Hallberg, Lecturer, Geosciences, Atmospheric and Oceanic Sciences, Geophysical Fluid Dynamics Laboratory

Alexander Smits, Eugene Higgins Professor and Chair of Mechanical and Aerospace Engineering

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Research Associates

Sean Bailey, visiting research collaborator
Chris Golaz
Jim Huang
Pino Martin, visiting research scholar, mechanical and aerospace engineering
Charles Talbot

Graduate Students

Dena Feldman
Clara Helm
Stimit Shah
Owen Williams

Undergraduate Students

Jonathan Goh '11
Jasmine Low '11
Emily Moder '13
Ida Posner '12
Laszlo Szocs '13