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▶ Past Seminars
Season 1 (20112012)
Season 2 (20122013)

▶ NIA Researcher/Faculty

Boris Diskin, Ph.D.
Research Fellow, NIA
Research Associate Professor,
Mechanical and Aerospace Engineering,
University of Virginia
Adjointbased optimization methods, Finitevolume discretizations, Multigrid methods on structured/unstructured grids
Web

Email

Elbert Jeyapaul, Ph.D.
Postdoctoral Fellow, NASA
Flow separation, Singlepoint turbulence modeling and LES.
Email

LiShi Luo, Ph.D.
The Richard F. Barry Jr. Distinguished Endowed Professor (in Residence, NIA)
Mathematics and Statistics,
Old Dominion University
Kinetic methods for CFD, Nonequilibrium flows, Complex fluids
Web

Email

Bill Moore, Ph.D.
Professor in Residence, NIA
Atmospheric & Planetary Sciences,
Hampton University
Thermal Evolution of Planet and Satellite Inteiors, Dynamical Evolution of Planets and Satellites, Coupled AtmosphereInterior Modeling of Planets, What Makes a Planetary Body Habitable?
Web

Email

Hiroaki Nishikawa, Ph.D.
Sr. Research Scientist, NIA
Viscous/inviscid discretization and convergence acceleration methods for unstructured grids
Web

Email

CFD Notes

Matteo Parsani, Ph.D.
Postdoctoral Fellow at NASA LaRC
highorder accurate methods for largeeddy simulation and aeroacoustics, efficient explicit and implicit time integrators and acceleration techniques for compressible flows

Email

Sriram Rallabhandi, Ph.D.
Sr. Research Engineer, NIA
Aircraft Design, Sonic Boom Modeling, MultiDisciplinary Design
Optimization, Aerodynamic Analysis, Computational Fluid Dynamics, Reduced Order Modeling and Model Order Reduction
Web

Email

Balaji Shankar Venkatachari, Ph.D.
Postdoctoral Fellow, University of Alabama at Birmingham
Resident at the NASA Langley Research Center in the Computational AeroSciences Branch,
working on numerical algorithm development, Hypersonics, TPS modeling (continuum and multiscale modeling), and CAA.
Email




NIA CFD Seminar Schedule
Click here to view the full list of videos.
Click the camera icon below to go directly to the video for each seminar.

04222014
11:00am  noon
NIA Room 141
video
Walsh Functions in Numerical Simulation: A New Framework for Solving Nonlinear Systems of PDEs
A segmented, orthonormal basis function set composed of Walsh Functions is used for deriving global solutions (valid over the entire domain) to nonlinear differential equations that include discontinuities. A powerful, selfmapping characteristic of this set is closure under multiplication  the product of any two elements of the set is also an element of the set: gn(x) gm(x) = gk(x) (xb  xa)^{1/2}. In the same way that Fourier series are used to generate global solutions to linear problems, this selfmapping property under multiplication allows similar approaches to nonlinear problems. A new derivation of the basis functions applies a fractallike algorithm (infinitely selfsimilar) focused on the distribution of segment lengths. Only two segment lengths are allowed in a group p. A recursivefolding algorithm that propagates fundamental symmetries to successive functions in the series determines the distribution of segment lengths. Functions, including those with discontinuities, may be represented on the domain as a series in gn(x) with no occurrence of a Gibbs phenomenon (ringing) across the discontinuity. Integrals and derivatives are computed using simple matrix multiplication of series representations of functions without the need for divided differences. A FORTRAN module for supporting Walsh function simulations is discussed. Examples are discussed for solution of the time dependent problems: an advection equation, a Burgers equation, and a Riemann problem.
Speaker Bio:

Dr. Peter Gnoffo is Senior Computational Aerothermodynamicist at NASA Langley Research Center. He earned his Ph.D in Mechanical and Aerospace Engineering at Princeton University in 1983. He joined NASA in 1974 after receiving a B.S. in Aerospace Engineering from Polytechnic Institute of Brooklyn. The subject lecture follows recent work published in the Journal of Computational Physics, Vol 258, pp 650688, Feb 2014, titled 'Global Series Solutions of Nonlinear Differential Equations with Shocks Using Walsh Functions.'


Relevant Publication:

"Global Series Solutions of Nonlinear Differential Equations with Shocks using Walsh Functions'",
Journal of Computational Physics, Volume 258, p. 650688.
[online ]


03042014
11:00am  noon
NIA Room 137
video
Development of Fast and Efficient CFD Tools, HexaGrid and FaSTAR
We have developed efficient CFD tools: an automatic hexahedra grid generator "HexaGrid" and a fast flow solver "FaSTAR". HexaGrid can generate Cartesianbased unstructured grids with bodyfitted layer grids just by inputting CAD geometry data and several control parameters such as surface grid sizes and domain sizes. Since the layer grids are generated by a projection method, the timeconsuming work that repairs gaps and overlaps of surface data is minimized. FaSTAR is a compressible flow solver of unstructured grids. It employs a simple facebased data structure and this helps performance optimization of the codes. An agglomerated multigrid method is also utilized to accelerate convergence. The octree data structure of the Cartesian grid is used for the agglomeration to keep the coarsegrid quality. Steady and unsteady simulations with HexaGrid and FaSTAR are presented at the seminar. We finally show a future outlook of CFD code development.
Speaker Bio:

Dr. Atsushi Hashimoto is a researcher at Japan Aerospace Exploration Agency (JAXA). He earned Ph.D. in Aerospace Engineering at Nagoya University, Japan in 2007. He joined JAXA in 2007. His area of expertise is aerodynamic prediction with unstructuredgrid CFD, aeroacoustics, and aeroelasticity.


Relevant Publication:

"Toward the Fastest Unstructured CFD Code 'FaSTAR'", AIAA20121075
[online]


02182014
11:00am  noon
NIA Room 101
video
Evaluation of Multigrid Solutions for Turbulent Flows
A multigrid methodology has been recently developed in a NASA solver, FUN3D, and
successfully applied for a wide range of turbulent flows, from simple twodimensional geometries to realistic threedimensional configurations.
The methodology is applicable to structured and unstructuredgrid solutions and includes both regular and agglomerated
coarse meshes. Significant speedups over singlegrid computations have been demonstrated.
In the current work, we report on a detailed evaluation of the solver performance in computing benchmark turbulent flows.
For those benchmark computations, multigrid solutions are compared with the corresponding singlegrid solutions
in terms of timetosolution characteristics measured in the same computing environment.
Multigrid efficiency enables a gridrefinement study of a turbulent
flow around an airfoil that is discussed in detail.
This talk is an extended version of the talk presented at AIAA SciTech2014 conference.
Speaker Bio:

Dr. Boris Diskin is Research Fellow at NIA. He earned Ph.D. in Applied Mathematics at The Weizmann Institute of Science, Israel in 1998. He was a Senior Research Scientist at ICASE and joined NIA from its inception in 2003. His area of expertise is adjointbased optimization and grid adaptation methods, finitevolume discretizations, and multigrid methods.



12032013
11:00am  noon
NIA Room 137
video
HigherOrder Moments and Their Modeling Approximations in a Turbulent
Channel Flow Subjected to Mean Strain.
Third and fourthorder moments and the budget terms in their transport equations are evaluated using results from Direct Numerical Simulations (DNS) of a turbulent channel flow at Re_tau = 395, to aid in the development of higherorder ReynoldsAveraged Navier Stokes (RANS) closure models. These models have been proposed as a means of obtaining more accurate predictions of complex flows. Strain has been applied to this channel to mimic a spatiallyevolving adverse pressure gradient flow leading to separation. Existing modeling hypothesis that relate higherorder moments to their lowerorder moments, such as gradient diffusion and assumed probability distribution functions have been tested. Insights into where to focus modeling efforts will be presented.
Speaker Bio:

Dr. Elbert Jeyapaul is a postdoctoral fellow at NIA, working on RANS turbulence modeling.
He received his doctorate in Aerospace engineering in 2011 from Iowa state university.



09242013
11:00am  noon
NIA Room 101
video
The MOOD Method  Multidimensional Optimal Order Detection  a first a posteriori approach to VeryHighOrder Finite Volumes methods.
This talk will be dedicated to the new type of very highorder Finite Volume methods for hyperbolic systems of conservation laws that I introduced and developed during my doctoral studies. This method, named MOOD for Multidimensional Optimal Order Detection, provides very accurate simulations for two and threedimensional unstructured meshes. The design of such a method is made delicate by the emergence of solution singularities (shocks, contact discontinuities) for which spurious phenomena (oscillations, nonphysical values creation, etc.) are generated by the highorder approximation. The originality of this work lies in a new treatment for theses problems. Contrary to classical methods which try to control such undesirable phenomena through an a priori limitation, we propose an a posteriori treatment approach based on a local scheme order decrementing. In particular, we show that this concept easily provides properties that are usually difficult to prove in a multidimensional unstructured framework (positivitypreserving for instance). The robustness and quality of the MOOD method have been numerically proved through numerous test cases in 2D and 3D for singlematerial compressible flows, and a significant reduction of computational resources (CPU and memory storage) needed to get stateoftheart results has been shown. I will moreover present some preliminary results on my current work at LANL for the case of multimaterial compressible flows.
Speaker Bio:

Dr. Steven Diot is Postdoctoral Research Associate at the Los Alamos National Laboratory. He received his Ph.D. degree in Applied Mathematics from the University of Toulouse (France) in 2012. During his Ph.D. research studies, he developed a new approach to VeryHighOrder Finite Volume methods for singlematerial compressible flows called the Multidimensional Optimal Order Detection (MOOD) method. An important part of his postdoctoral studies is the extension of the MOOD method to multimaterial compressible flows and to coupled physics.
[ Home Page 
PhD Defense Slides 
Awardwinning movie ]



09102013
11:00am  noon
NIA Room 141
video
Nonequilibrium Pressure Considerations in Modeling Viscous Rotating Flows
Hamilton's Principal of Least Action has been employed to incorporate nonequilibrium fluid behavior in the study of simple viscous flows. The original goal was to clarify the role of bulk viscosity in modeling highspeed viscous and reacting flows.[1,2] The theory demonstrated that bulk viscous transport effects and nonequilibrium density effects coexisted, but were intertwined. Employing acousticallybased estimates for this overall bulk viscous effect, the theory predicted correctly the densityjump and shock thickness for air flows at various Mach numbers.[2] The theory also exhibited a separate nonequilibrium pressure effect, and the associated pressure relaxation coefficient could be estimated using acoustic data. Recentlypublished work [3] has identified a possible new lowspeed sound source, while predicting that pressure deficits within the central cores of tornadoes and dust devils (and similarly aircraft trailing line vortices) can be substantially larger than equilibriumbased estimates. Modifying the NavierStokes equations to incorporate nonequilibrium pressure gradient forces in simple vortical flows resulted in an exact solution for an axial vortex [3] that bypasses the shear stress discontinuity found in Rankine vortex models by way of a a sheathlike nonequilibrium pressure zone that effectively isolates a rigidlyrotating central fluid region from an outer potential vortex region. Subsequently, the nearisolation of such a rotating central fluid column has been used to show that nonequilibrium pressure gradient forces can control the height of the central column. [4] The rotating column solution was employed successfully to predict the heights of terrestrial dust devil columns.
Nonequilibrium pressure gradient forces offer the potential for modeling Mars dust devil behavior more accurately, possibly enabling the estimation of maximum pressure deficits and swirl velocities via satellite observation. Of potentially greater importance, the theory may explain how streaks are formed and sustained in the wall region of turbulent boundary layers and thus offer the potential for improved turbulence models.
Speaker Bio:

Dr. Robert L. (Bob) Ash joined the engineering faculty at Old Dominion University at the time when LaRC was heavily involved in the design and development of their spectacularly successful Viking missions to Mars. His research has been sponsored primarily by NASA, and accomplishments have ranged from coinventing riblets for turbulent skin friction drag reduction through determination that the most costeffective and practical way to accomplish sample return and human missions to Mars was to manufacture the rocket propellant required for the return trip in situ using local Mars water and carbon dioxide (while he was working as a National Research Council Senior Resident Researcher at JPL). He and nowretired LaRC scientist, Dr. Allan J. Zuckerwar, have been collaborating for more than 30years, working to develop a better understanding of the role of bulk viscosity in modeling fluid behavior, and that effort has led to the work that will be discussed in this seminar. Professor Ash is designated as an Eminent Scholar in the Mechanical and Aerospace Engineering Departmetn at Old Dominion University.
[ Home Page ]


Relevant Publications:

1. Zuckerwar, A. J. and R.L. Ash, "Variational approach to the volume viscosity of fluids", Physics of Fluids, Vol. 18, 047101 (10 pages), April 2006.
[ journal ]
2. Zuckerwar, A.J., and R.L. Ash, "Volume viscosity in fluids with multiple dissipative processes", Physics of Fluids, Vol. 21, 033105 (12 pages), March 2009.
[ journal ]
3. Ash, R.L., I. Zardadkhan, and A.J. Zuckerwar, "The influence of pressure relaxation on the structure of an axial vortex", Physics of Fluids, Vol. 23, 073101, (12 pages), July 2011.
[ journal ]
4. Ash, R.L. and I.R. Zardadkhan, "Nonequilibrium pressure control of the height of a largescale, groundcoupled, rotating fluid column", Physics of Fluids, Vol. 25, 053101, (20 pages), doi: 10.1063/1.4807068, May 2013.
[ journal ]


08272013
11:00am  noon
NIA Room 141
video
Chaotic adjoint: from massive linear algebra to a lightweight wrapper of existing solvers
Many high fidelity unsteady flow simulations at high Reynolds number exhibit chaotic dynamics. Failure of conventional tangent and adjoint solvers for these simulations has been demonstrated on flow solvers including FUN3D. The Least Squares Shadowing approach recently developed by the speaker overcomes the illconditioning of chaotic dynamical system, and lead to stable tangent and adjoint sensitivity analysis. This talk will start with the problem faced in chaotic adjoint. We then introduce the Least Squares Shadowing approach, and the massive spacetime 4D linear system it requires to solve. Finally, we show how solving the linear system can be reduced to a lightweight wrapper of an existing PDE and adjoint solver.
Speaker Bio:

Dr. Qiqi Wang is Assistant Professor of Aeronautics and Astronautics
in Massachusetts Institute of Technology. His areas of expertise include design, optimization and
uncertainty quantification, unsteady flows, aeroelastics and aeromechanics, computational sensitivity analysis.
[ Home Page ]



