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Tea Seminar : Friday, May 24, 2019 - 4:30pm : Speaker(s): Mr. Angxiu Ni
Abtract:

Turbulence is an important example of chaotic dynamical systems, and sensitivity analysis is a powerful tool for design via computation.  However, traditional sensitivity methods explode for chaotic systems, posing the challenge we will address in this talk.  We first review how to compute meaningful derivatives of long-time-averaged objectives in chaotic systems via the shadowing method, which we then reformulate as a 'non-intrusive' minimization problem on the unstable subspace. Then we show a recent adjoint shadowing theorem, based on which we develop an adjoint sensitivity algorithm, NI... Read More

Bio:
Mr. Angxiu Ni (pronounces as ang-shyou-knee) got his BS in Mechanical Engineering from Tsinghua University. He then got two MS, one at Tsinghua University working with Professor Haixin Chen, one at... Read More
Tea Seminar : Friday, May 3, 2019 - 4:30pm : Speaker(s): Mr. Seyedshahabaddin (Shahab) Mirjalili
Abtract:

From oceanic breaking waves to atomization of liquid fuels for combustion, two-phase flows are omni-present in natural and industrial settings. Despite decades of numerical method development, due to the many challenges involved in simulation of realistic two-phase flows, no gold-standard has yet emerged in the literature. In this study, we present a novel diffuse interface method that addresses various challenges for simulation of incompressible, immiscible two-phase flows. The boundedness of this mass-conserving interface-capturing method is proven analytically. Then, a comparison of the... Read More

Bio:
Shahab Mirjalili defended his PhD in Mechanical Engineering at Stanford University in March 2019. During his PhD under the supervision of Professor Ali Mani, he focused on development of numerical... Read More
Tea Seminar : Friday, April 26, 2019 - 4:30pm : Speaker(s): ICME / CTR Visiting Associate Professor Qiqi Wang
Abtract:

What is the future of computing? Some believe it's big data. For others, it's big computation. Supporters of big data believe that most problems can be solved by gathering huge amounts of data and applying machine learning. Those who believe in big computation, however, postulates that all phenomena in the world can be explained by solving simple physical equations with sufficient computational power. Who is right? In this talk, I will give my personal view on this question.

Bio:
Qiqi Wang (pronounces as Chi-chi Wong) got his BS in mathematics from University of Science and Technology at Hefei, China. He then got his Ph.D. in Computational and Mathematical Engineering at... Read More
Tea Seminar : Friday, April 5, 2019 - 4:30pm : Speaker(s): Dr.-Ing. Lin Fu
Abtract:

Shock-wave/boundary-layer interactions are typical flow phenomena in hypersonic flows. In this study, large-scale DNS and equilibrium wall-modeled LES (WMLES) are employed to investigate and predict the physical processes responsible for the intense overheating downstream from the shock-impingement region, where the boundary layer suddenly transitions to turbulence.  (1) At low shock incidence angles, the post-shock transition strongly depends on the inlet disturbances, e.g. the amplitude and the random phase. WMLES has difficulties to replicate the DNS statistics due to the fact that coars... Read More

Bio:
Dr.-Ing. Lin Fu is a Postdoctoral Fellow of CTR at Stanford University since January 2018. He is now working on hypersonic flows in Prof. Moin’s group. Before he joined CTR, he obtained his Ph.D.... Read More
Tea Seminar : Friday, March 15, 2019 - 4:30pm : Speaker(s): Dr. Quentin Douasbin
Abtract:

Combustion devices are prone to combustion instabilities (CIs). They classically occur when heat release rate oscillations and acoustic fluctuations become coherent, creating constructive interferences. To predict the occurrence of CIs in combustion devices, one must account for 1) the acoustic waves in the entire combustion system and 2) the flame response to these fluctuations. The former can only be obtained if the acoustic properties of the boundaries are properly prescribed. During this seminar, a Time Domain Impedance Boundary Condition (TDIBC) method will be presented as well as a mo... Read More

Bio:
Before joining the CTR, Dr. Quentin Douasbin was a Postdoctoral Fellow at CERFACS, Toulouse, France, where he worked on the development of CFD software for industrial partners. He received his Ph.D.... Read More
Tea Seminar : Friday, March 1, 2019 - 4:30pm : Speaker(s): Dr. Mario Di Renzo
Abtract:

The impingement of electric fields on flames is known to have potential for mitigating combustion instabilities, enhancing flame propagation, and decreasing pollutant emissions. In particular, electric fields can be used to steer ions produced inside the flame in opposite directions depending on their sign. These ions collide and exchange momentum with the surrounding neutral molecules, which leads to modifications in the flow field. In this talk, steady axisymmetric numerical simulations of methane/air counterflow laminar diffusion flames are employed in order to analyze the effects of the... Read More

Bio:
Before joining the CTR as a Postdoctoral fellow, Dr. Di Renzo was a researcher at Politecnico di Bari, Italy, where he received his BS and MS in Mechanical Engineering as well as his Ph.D. under the... Read More
Tea Seminar : Friday, February 15, 2019 - 4:30pm : Speaker(s): Dr. Adrián Lozano-Durán
Abtract:

Turbulent flows in the presence of bounding surfaces, as those occurring in oceanic and atmospheric currents, around vehicles, or inside pipes, may be apprehended as a collection of whirls or eddies. These eddies follow a regeneration cycle, i.e, existing eddies are seeds for the origin of new ones and so forth.  Understanding this process is critical for the modeling and control of geophysical and industrial flows where a non-negligible fraction of the energy is dissipated by turbulence in the immediate vicinity of walls. In the present work, we examine the causal interactions among energy... Read More

Bio:
Dr. Adrian Lozano-Duran received his PhD from the Technical University of Madrid in 2015 at the Computational Fluid Mechanics Lab. headed by Prof. Jiménez. His main research has focused on... Read More
Tea Seminar : Friday, January 25, 2019 - 4:30pm : Speaker(s): Visiting Associate Professor Antonino Ferrante
Abtract:

We have developed a new pressure-correction method for simulating incompressible flows over curved walls. The methodology is applicable to DNS, LES and RANS. We chose the orthogonal formulation of the Navier-Stokes equations in curvilinear coordinates vs the generalized curvilinear coordinates because the computational cost of advancing the numerical solution of the governing equations in time is substantially reduced as the orthogonal formulation does not contain cross-derivatives in the advection, diffusion, Laplacian, and gradient operators. As a result, the numerical stencils of the fin... Read More

Bio:
Professor Antonino Ferrante is an Associate Professor of the William E. Boeing Department of Aeronautics & Astronautics at the University of Washington (UW), Seattle, where he leads the... Read More
Tea Seminar : Friday, January 18, 2019 - 4:30pm : Speaker(s): Dr. Andrea Lani
Abtract:

The COOLFluiD (Computational Object Oriented Libraries for Fluid Dynamics) project, which started in 2002 as a joint effort between the Von Karman Institute for Fluid Dynamics (VKI) and the Center for mathematical Plasma Astrophysics (CmPA) at the University of Leuven (KUL), has led to the development of a world-class open source platform for HPC and multi-physics modelling. Within this framework, research efforts have been devoted particularly to the modeling of space re-entry aerothermodynamics and magnetized plasmas. The former includes the development of models/algorithms for simulating... Read More

Bio:
Dr. Andrea Lani is currently Research Expert at the Center for Mathematical Plasma Astrophysics (CmPA) at KU Leuven and Director of the Leuven Computational Modeling Center (LCMC). Previously, he has... Read More
Tea Seminar : Friday, January 11, 2019 - 4:30pm : Speaker(s): Dr. Jinah Jeun
Abtract:

In this talk we investigate amplifying behavior of small perturbations about Reynolds-averaged Navier-Stokes solutions of high-speed turbulent jets using input-output (I/O) analysis.  Inspired by control theory in electrical engineering, our method investigates how input forcing (jet turbulence) leads to output noise.  Singular value decomposition of the resolvent of the linearized Navier-Stokes equations forms an orthonormal set of I/O mode pairs, sorted in descending order by the magnitude of the corresponding singular values.  In this way we find that the input modes capture coherent str... Read More

Bio:
Dr. Jinah Jeun was a Postdoctoral Associate in the Department of Aerospace Engineering and Mechanics at the University of Minnesota. She received her BS degree in Aerospace Engineering from Korea... Read More

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