Conferences, Lectures, & Seminars
Events for November
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Modeling Combustion with Detailed Chemistry
Wed, Nov 07, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Zhuyin Ren Ph.D.Cornell UniversitySibley School of Mechanical & Aerospace EngineeringAbstractCombustion modeling is now playing an important role in the design and optimization of
advanced combustion devices such as internal combustion engines and gas turbine
combustors. For high-fidelity combustion modeling, it is essential, though challenging, to
resolve the highly nonlinear turbulence-chemistry interaction and to predict the emissions
of pollutants such as NOx and particulates. This requires the accurate description of
turbulent mixing as well as the use of detailed chemistry.In this talk, recent progresses in PDF methods for turbulent reactive flows, particularly
the sensitivity analysis, will be described and demonstrated. Then the talk will focus on
presenting the ICE-PIC dimension-reduction method and the ISAT storage-retrieval
method for the efficient implementation of detailed chemistry in combustion modeling.
The theoretical basis, validation, and computational efficiency of these methods will be
described. This talk will also describe the x2f_mpi software for efficient chemistry
calculations in large-scale parallel simulations. It will conclude with a discussion on
applying the ICE-PIC, ISAT, x2f_mpi algorithms to incorporate detailed chemistry in
combustion simulations.Location: Stauffer Science Lecture Hall, Rm 102
Audiences: Everyone Is Invited
Contact: April Mundy
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Measuring unsteady efficiency and performance of biological and bio-inspired propulsors
Wed, Nov 14, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Prof. John O. DabiriGraduate Aeronautical Laboratories and BioengineeringCalifornia Institute of TechnologyAbstract:
This talk will describe the development of new experimental and analytical
tools to extract the governing mechanisms of animal swimming and flying
from empirical observations. The approach advocated presently avoids
direct use of the vorticity field in favor of a Lagrangian,
particle-tracking perspective. The benefits of this strategy are
demonstrated in laboratory studies of the bluegill sunfish and various
jellyfish species. These laboratory observations are complemented by
inexpensive computational models and a new in situ field apparatus, which
enables a SCUBA diver to make velocimetry measurements normally confined
to artificial laboratory environments. The principles derived from these
studies are applied to fluid dynamic problems as varied as autonomous
underwater vehicle design, cardiovascular flow diagnostics, and wind energy harvesting.Location: Stauffer Science Lecture Hall, Rm 102
Audiences: Everyone Is Invited
Contact: April Mundy
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Title: Examination of the link between aerosol properties and cloud droplet activation efficiency
Wed, Nov 21, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Don CollinsAssociate ProfessorDept. of Atmospheric SciencesTexas A & M UniversityAbstract:Among the factors contributing to the overall uncertainty in the indirect effect of aerosols on climate is the still inadequately understood relationship between particle size, composition, and critical supersaturation. Applying the results of laboratory studies of the activation efficiency of relatively simplistic aerosols to predict CCN concentration for an ambient aerosol for which only an incomplete description of its size distribution and composition is available is undoubtedly challenging, as is reflected in the varied success of several recent CCN closure efforts. Whereas an understanding of the link between composition and critical supersaturation is ultimately needed, insight into the factors controlling activation can be gained through an improved understanding of the relationship between hygroscopic growth under subsaturated conditions and cloud droplet formation under supersaturated conditions.
I will describe both our recent efforts aimed at quantifying the link between critical supersaturation and hygroscopicity, and our recent development and use of an instrument that permits quantification of the link between critical supersaturation and composition.Location: Stauffer Science Lecture Hall, Rm 102
Audiences: Everyone Is Invited
Contact: April Mundy
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Global Modes and Aerodynamic Sound Generation In Self-Excited Hot Jets
Wed, Nov 28, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Lutz Lesshafft Postdoctoral Fellow University of California at Santa Barbara Santa Barbara, CA One of the most remarkable phenomena in the field of aerodynamic instability is the spontaneous bifurcation of a steady flow towards a selforganized state of intrinsic oscillations. Similar to the von Kármán vortex street in cylinder wakes, hot jets constitute another class of such globally unstable flows: whereas an isothermal jet behaves as an amplifier of external perturbations, sufficiently heated jets display intrinsic oscillations in the form of regularly spaced ring vortices. Comparison of direct numerical simulation results to theoretical predictions, derived from Ginzburg-Landau model equations, demonstrates that these self-sustained oscillations in subsonic hot jets are dominated by the dynamics of a nonlinear wave front, which separates an oscillating flow region from the upstream steady flow. The bifurcation towards a state of self-sustained synchronized oscillations ('nonlinear global mode') is due to the existence of an absolutely unstable region in the underlying base flow. A linear stability analysis allows us to predict the naturally selected frequency, as well as the critical temperature ratio for the onset of global instability. Both the near- and the far-field of the jet are resolved via DNS: the acoustic field generated by such a synchronized vortex street is found to be that of a compact dipole, with maximum acoustic intensity in the axial direction of the jet. A numerical analysis of the Lighthill equation reveals that this radiation pattern is due to strong entropy fluctuations within the jet.
Location: Stauffer Science Lecture Hall, Rm 102
Audiences: Everyone Is Invited
Contact: April Mundy