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CTR events

Tea Seminar : Friday, January 24, 2020 - 4:30pm : Speaker(s): Dr. Isabel Houghton
Abtract:

Biologically generated turbulence has been proposed as an important contributor to nutrient transport and ocean mixing. However, for swimming animals to produce non-negligible transport and mixing, they must produce eddies at scales comparable to the length scales of stratification in the ocean. It has previously been argued that biologically generated turbulence is limited to the scale of the individual animals involved, which would make turbulence created by highly abundant centimeter-scale zooplankton such as krill irrelevant to ocean mixing. Their small size notwithstanding, zooplankton... Read More

Bio:
Dr. Isabel Houghton is currently a postdoctoral fellow at the Data Institute of University of San Francisco (USF) utilizing data science techniques to conduct research on observing oceanic dynamics.... Read More
Tea Seminar : Friday, January 10, 2020 - 4:30pm : Speaker(s): Dr. Maxime Bassenne
Abtract:

Unconditionally stable implicit time-marching methods are powerful in efficiently solving stiff differential equations. In this talk, I will present a novel unified framework for handling both physical and numerical stiffness based on Time-Accurate and highly-Stable Explicit (TASE) operators.

The proposed TASE operators act as preconditioners on the stiff terms and can be readily deployed to most existing explicit time-marching methods. The resulting time integration method remains the original explicit time-marching schemes, yet with nearly unconditional stability. The TASE operator... Read More

Bio:
Dr. Maxime Bassenne is a postdoctoral research fellow in the Laboratory of Artificial Intelligence in Medicine and Biomedical Physics in the Stanford Radiation Oncology department. He received his... Read More
Tea Seminar : Friday, December 13, 2019 - 4:30pm : Speaker(s): Professor and Chair Snezhana I. Abarzhi
Abtract:

Interfacial mixing and transport are nonequilibrium processes coupling kinetic to macroscopic scales. They occur in plasmas, fluids, and materials over celestial events to atoms. Grasping their fundamentals can advance a broad range of disciplines in science, mathematics, and engineering. This work focuses on the long-standing classic problem of stability of a phase boundary - a fluid interface that has a mass flow across it. We briefly review the recent advances and challenges in theoretical and experimental studies, develop the general theoretical framework directly linking the microscopi... Read More

Bio:
Snezhana Abarzhi works at the University of Western Australia as Professor and Chair of Applied Mathematics. Before the University of Western Australia, she worked at Carnegie Mellon University,... Read More
Tea Seminar : Friday, November 15, 2019 - 4:30pm : Speaker(s): Professor Michael E. Mueller
Abtract:

Turbulent combustion is an extremely challenging “multi-multi” problem: multi-physics, multi-scale, and multi-species. Since not all scales of turbulence and combustion can be resolved in DNS for practical conditions of interest, models are required for the unresolved turbulent combustion processes in LES and RANS. However, the large number of thermochemical scalars required to describe combustion chemistry (potentially hundreds or thousands of chemical species) means that the unresolved state-space that needs to be modeled is extremely high-dimensional. Turbulent combustion models can gene... Read More

Bio:
Michael E. Mueller is an Associate Professor in the Department of Mechanical and Aerospace Engineering at Princeton University, an associated faculty member in the Princeton Institute for... Read More
Tea Seminar : Friday, November 1, 2019 - 4:30pm : Speaker(s): Dr. Michael Adler
Abtract:

Swept shock-wave/turbulent-boundary-layer interactions (STBLIs) exhibit key dynamical differences from their spanwise-homogeneous counterparts, including the suppression of a dominant mechanism of low-frequency unsteadiness. An extensive database of wall-resolved simulations is constructed to examine the differences between the properties of spanwise-homogeneous, swept, and compound swept interaction classes. A novel method for calculating the dynamic linear response of these unsteady flows is also presented, which allows for the identification and characterization of absolute instabilities... Read More

Bio:
Dr. Michael Adler received his PhD in Aeronautical and Astronautical Engineering from The Ohio State University in 2019, where his research examined many aspects of shock-wave/turbulent-boundary-... Read More
Tea Seminar : Friday, October 25, 2019 - 4:30pm : Speaker(s): Dr. Hyun Ji (Jane) Bae
Abtract:

The resolvent formulation of McKeon & Sharma (2010) is applied to supersonic turbulent boundary layer flows in order to study the validity of Morkovin’s hypothesis, which postulates that high-speed turbulence structure in zero pressure-gradient turbulent boundary layers remains largely the same as its incompressible counterpart. The resolvent analysis highlights two distinct regions of the supersonic turbulent boundary layer in the wave parameter space: the relatively supersonic region and the relatively subsonic region. The relatively supersonic region, where the flow is supersonic rel... Read More

Bio:
Dr. Hyun Ji Bae is a postdoctoral scholar at the Department of Aerospace at Caltech. She received her Ph.D. from Stanford University in 2018 in Computational and Mathematical Engineering. Her main... Read More
Tea Seminar : Tuesday, September 3, 2019 - 10:00am : Speaker(s): Dr. Andrew Trettel
Abtract:

A recent mean velocity transformation (Trettel and Larsson 2016) converts compressible mean velocities into equivalent incompressible mean velocities.  This transformation works properly for channel flows but does not work properly for boundary layers.  A two-dimensional extension of this transformation reveals the inherent limitations in the transformation as an extension of the incompressible law-of-the-wall.  The transformation cannot properly transform the outer layer coordinate in boundary layers, and the error associated with this correlates highly with the error in the transformation... Read More

Bio:
Dr. Andrew Trettel received his PhD in mechanical engineering from the University of California, Los Angeles in 2019. Trettel’s recent research has been in developing and improving scaling laws for... Read More
Tea Seminar : Friday, August 23, 2019 - 4:30pm : Speaker(s): Professor Jan Nordström
Abtract:

The study of so called transmission problems in  [2] revealed that successful numerical filtering may include a delicate balance between the need to remove high frequency oscillations (filter often for accuracy) and the need to avoid possible growth  (filter seldom for stability).  In this talk we investigate this contradiction, and propose different avenues for improved functionality.

The filter operators derived in [1] are the basic building  blocks.  We demonstrate that explicit use of the basic filter operators guarantee accuracy but lead to instabilities, while an implicit imple... Read More

Bio:
Since 2010 Dr. Jan Nordström is a Professor in Scientific Computing and since 2012 he is the Head of Division of Computational Mathematics, in the Department of Mathematics, at Linköping University (... Read More
Tea Seminar : Thursday, August 22, 2019 - 10:00am : Speaker(s): Dr. Zhao Wu
Abtract:

An unsupervised machine-learning algorithm, the self-organizing map (SOM), is used to identify the turbulent boundary layer (TBL) and non-TBL regions in bypass transition. The data employed for the analysis are from an archived direct simulation publicly available in the Johns Hopkins Turbulence Databases (JHTDB, http://turbulence.pha.jhu.edu). The data points in the entire flow domain are automatically classified into TBL and non-TBL regions by the SOM, based on their standardized velocity, velocity fluctuations, velocity gradients and their spatial locations. Thus the SOM identifies the t... Read More

Bio:
Dr. Zhao Wu received his doctoral degree in Mechanical Engineering from The University of Manchester, UK in 2017. During his PhD, his research was focused on direct numerical simulations of fluid... Read More
Tea Seminar : Wednesday, August 21, 2019 - 10:00am : Speaker(s): Mr. Xiaoyi Lu, Ph.D. Candidate
Abtract:

Lu presents findings on the hydrodynamic stability of a premixed flame subjected to transverse shear. The problem configuration is a situation of interest for laminar and turbulent flames when they travel into a region of shear.

The linear stability problem is first analytically solved, and the dispersion relation is determined. The effects of the transverse shear and thermal expansion are examined. Lu’s research then carried out a weakly nonlinear analysis in the weak thermal expansion limit and derived the modified Michelson-Sivashinsky (MS) equation, which describes the evolution... Read More

Bio:
Mr. Xiaoyi Lu is a Ph.D. Candidate in Theoretical and Applied Mechanics at the University of Illinois at Urbana-Champaign. He received his B.S. degree in Mechanical Engineering from the University of... Read More

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