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CTR events

CTR Tea : Friday, November 10, 2017 - 4:30pm : Speaker(s): Dr. Hiroyuki Abe
Abtract:

Separation and reattachment of a turbulent boundary layer are crucial issues in aeronautical and engineering applications since they are associated with upper bound of efficiency for the devices. Understanding of the underlying physics and the accurate prediction however may not be still sufficient especially for pressure-induced separated flows. In the present work, we have performed a series of direct numerical simulations (DNSs) for a pressure-induced turbulent separation bubble on a flat plate. Suction and blowing are imposed at the upper boundary for producing a separation bubble. The... Read More

Bio:
Dr. Hiroyuki Abe is an Associate Senior Researcher in Japan Aerospace Exploration Agency. He received his PhD in Mechanical Engineering from Tokyo University of Science in 2002. His research... Read More
CTR Tea : Friday, November 3, 2017 - 4:30pm : Speaker(s): Kookjin Lee
Abtract:

We consider the numerical solution of parameterized linear systems where the system matrix, the solution, and the right-hand side are parameterized by a set of uncertain input parameters. We explore spectral methods in which the solutions are approximated in a chosen finite-dimensional subspace. It has been shown that the stochastic Galerkin projection technique typically does not minimize any measure of the solution error. As a remedy for this, we propose a novel stochastic least-squares Petrov–Galerkin (LSPG) method. The proposed method is optimal in the sense that it produces the solutio... Read More

Bio:
Kookjin Lee is a Ph.D. candidate in the Computer Science department at the University of Maryland College Park, working with Professor Howard Elman. Kookjin’s primary research interest lies in... Read More
CTR Tea : Friday, October 20, 2017 - 4:30pm : Speaker(s): Dr. Xinyu Zhao
Abtract:

Radiative heat transfer process in combustion systems has received relatively little attention to date. Recently, it starts to generate increasing interest given the current trends of engine designs for both internal combustion engines and aeronautical engines. Meanwhile, the need to properly model radiative heat transfer in fire-related scenarios is another driver of the interest. Radiation inside combustion systems is a complex process involving the interactions between spectral gases, soot, droplets, turbulence and the enclosure geometry. Gasses and soot/wall have distinct emission and a... Read More

Bio:
Dr. Xinyu Zhao is an Assistant Professor at the University of Connecticut. She joined the Mechanical Engineering Department in 2015 Spring, and prior to that, she was a postdoctoral research fellow... Read More
CTR Tea : Friday, September 29, 2017 - 4:30pm : Speaker(s): Dr. Perry Johnson
Abtract:

The dynamics of velocity gradients in turbulent flows not only represent an attractive way to explore theoretical issues such as intermittency, but also prove important for a number of micro-physical processes that occur in turbulent environments. Inspired by the qualitative success of the restricted Euler model for Lagrangian evolution of velocity gradients, this talk will introduce a stochastic Lagrangian model carefully constructed for homogeneous isotropic turbulence. Using the local isotropy hypothesis, it will be demonstrated how such a model can be applied in large-eddy simulations (... Read More

Bio:
Dr. Perry Johnson recently finished his PhD in Mechanical Engineering at Johns Hopkins and joined CTR as a postdoctoral scholar this September 2017. His research interests include small-scale... Read More
CTR Tea : Friday, September 22, 2017 - 4:30pm : Speaker(s): Dr. Michael Karp
Abtract:

In this talk several aspects of transition to turbulence in wall-bounded shear flows are addressed. One aspect discusses the formation and evolution of coherent structures, such as counter-rotating vortex pairs (CVPs) and hairpins, observed in various transitional as well as turbulent flows. The vortex dynamics is followed using a novel analytical-based numerical method for the evolution of localized disturbances in homogenous shear base-flows. Using insights gained from the evolution of localized disturbances, a minimal element model, capable of following the evolution of packets of hairpi... Read More

Bio:
Dr. Michael Karp is a Postdoctoral Fellow in the Center for Turbulence Research at Stanford University. Karp received all of his degrees from the Faculty of Aerospace Engineering, Technion (BSc 2007... Read More
CTR Tea : Friday, September 8, 2017 - 4:30pm : Speaker(s): Professor Karthik Duraisamy
Abtract:

This talk will address the issue of sub-grid closure in large eddy simulations, leveraging ideas from non-equilibrium statistical mechanics. The approach is based on the Mori-Zwanzig (M-Z) formalism, which provides a framework to re-cast a high-dimensional dynamical system into an equivalent, lower-dimensional system. In this reduced system, which is in the form of a generalized Langevin equation (GLE), the effect of the unresolved modes on the resolved modes appears as a convolution integral (which is sometimes referred to as memory). The appearance of the memory term in the GLE demonstrat... Read More

Bio:
Karthik Duraisamy is an Associate Professor of Aerospace Engineering at the University of Michigan, Ann Arbor. He obtained a doctorate in aerospace engineering and masters in applied mathematics from... Read More
CTR Tea : Friday, September 1, 2017 - 4:30pm : Speaker(s): Jan Nordström
Abtract:

We derive boundary conditions for the nonlinear incompressible Navier-Stokes equations following the general recipie given in [1]. We present two formulations stemming from different techniques to diagonalize the boundary terms. Both formulations lead to an energy estimate.

In the first formulation, the boundary conditions are obtained through a suitable set of rotations. In the second formulation, the boundary conditions are derived directly by a standard eigenvalue decomposition [2, 3]. The two formulations differ in character and have different pro’s and con’s.

The rotationa... Read More

Bio:
Since 2010 Jan Nordström is a Professor in Scientific Computing and since 2012 serves as the Head of the Division of Computational Mathematics, Department of Mathematics, Linköping University. He... Read More
CTR Tea : Friday, August 25, 2017 - 4:30pm : Speaker(s): Fazlolah Mohaghegh (Ehsan)
Abtract:

This study shows recent developments in the Smoothed Profile Method (SPM) as a diffuse-interface approach. SPM is well suited towards simulating the dynamics of dense particulate flows at the meso-scale, i.e. when particles are resolved. Several challenges are addressed: extension of the diffuse interface method for a wide range of Reynolds numbers, tackling the stability of computations in an FSI setting with added mass effects, and developing a parallel implementation with adaptive mesh refinement to handle large ensembles of particles. This research also offers a new particle collision m... Read More

Bio:
Fazlolah Mohaghegh (Ehsan) is a PhD Candidate at the University of Iowa working under supervision of Professor Udaykumar. He received his BS and MS in Mechanical Engineering from Sharif University of... Read More
CTR Tea : Friday, August 18, 2017 - 4:15pm : Speaker(s): Professor Peter Schmid
Abtract:
In recent years, PDE-constrained optimization has become an effective and efficient tool in the analysis of complex fluid systems. Inherent stability, receptivity to external or internal forcing, or sensitivity to uncertainties or imperfections of fluid systems can be treated within this approach. We will present a computational framework based on this concept and demonstrate its ability to extract relevant information from numerical simulations, with examples from aero-acoustics, inertial mixing, roughnes... Read More
Bio:
Peter Schmid is Chair Professor of Applied Mathematics and Mathematical Physics at Imperial College London. Before joining Imperial he held a research director position at the French National... Read More
CTR Tea : Friday, August 4, 2017 - 4:15pm : Speaker(s): Dr. Xiang I. A. Yang
Abtract:

The cascading process of turbulent kinetic energy from large-scale fluid motions to small-scale and lesser-scale fluid motions in isotropic turbulence may be modeled as a hierarchical random multiplicative process according to the multifractal formalism. In this work, we show that the same formalism might also be used to model the cascading process of momentum in wall-bounded turbulent flows. However, instead of being a multiplicative process, the momentum cascade process is additive. The proposed multifractal model is used for describing the flow kinematics of the low-pass filtered streamw... Read More

Bio:
Dr. Xiang I. A. Yang is a Postdoctoral Fellow in the Center for Turbulence Research at Stanford University. Yang received his Bachelor’s degree in Mechanical Engineering from Peking University in... Read More

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