National Institute of Aerospace
Computational Fluid Dynamics Seminar

A place to share ideas and problems for barrier-breaking developments

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▶ Contacts

Boris Diskin   [ E-mail ]
Hiroaki Nishikawa   [ E-mail ]

▶ Past Seminars

    Season 7 (2017-2018)
    Season 6 (2016-2017)
    Season 5 (2015-2016)
    Season 4 (2014-2015)
    Season 3 (2013-2014)
    Season 2 (2012-2013)
    Season 1  (2011-2012)

    List of Speakers

▶ NIA Researchers
Boris Diskin, Ph.D.  
Research Fellow, NIA

Adjoint-based optimization methods, Finite-volume discretizations, Multigrid methods on structured/unstructured grids
Web | E-mail
David Del Rey Fernández, Ph.D.  
Postdoctoral Fellow, NIA

Robust high-order numerical methods for the solution of partial differential equations.
Prahladh S. Iyer Ph.D.  
Postdoctoral Fellow, NIA

DNS/ LES of complex flows, transition to turbulence and turbulence modeling.
Heather Kline Ph.D.  
Research Engieer, NIA

Adjoint-based design, transition to turbulence, and hypersonic air-breathing propulsion
Yi Liu, Ph.D.  
Senior Research Scientist, NIA

high-order accurate methods, turbomachinery and rotorcraft applicaitons.
Hiroaki Nishikawa, Ph.D.  
Associate Research Fellow, NIA

Discretization and convergence acceleration methods for unstructured grids
Web | E-mail | CFD Notes   View Hiroaki Nishikawa's LinkedIn profile Follow HiroNishikawa on Twitter
Juliette Pardue  
PhD Student, ODU/NIA

Mesh generation, parallel algorithms, and computational geometry.
Pedro Paredes, Ph.D.  
Research Engineer, NIA

Linear flow instability and control of complex flows and study of laminar-turbulent transition in compressible boundary layers
Balaji S. Venkatachari, Ph.D.  
Sr. Research Engineer, NIA

Numerical algorithm development, Hypersonics, TPS modeling (continuum and multi-scale modeling), and CAA.
Ali Uzun, Ph.D.  
Sr. Research Scientist, NIA

Computational fluid dynamics using high-order numerical methods, turbulence simulations, computational aeroacoustics and parallel computing.
Li Wang, Ph.D.  
Sr. Research Engineer, NIA

Turbulent flow simulation and modeling, high-order finite element CFD methods, adjoint-based sensitivity analysis and design optimization, adaptive meshing, multigrid acceleration strategies, and highperformance computing.
Beckett Zhou, Ph.D.  
Research Scholar, NIA

Adjoint-based design optimization, computational aeroacoustics and hybrid RANS/LES methods
▶ Faculties in Residence
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 Atmosphere-Interior Modeling of Planets, What Makes a Planetary Body Habitable?
Web | E-mail

NIA CFD Seminar Schedule

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108th NIA CFD Seminar:

10-01-2018   11:00am-noon (EDT)   NIA Room 137      video

Overset mesh and related technology in scFLOW

scFLOW is a commercial CFD code developed by Software Cradle since 2016. I introduced the overset mesh technology of SC/Tetra at NIA seminar in 2014. scFLOW is a successor product of SC/Tetra. scFLOW is based on a cell-centered discretization while SC/Tetra is based on a node-centered discretization. Unstructured polyhedral cells can be used for a computational mesh, and both pressure-based and density-based FVM solvers have been implemented for incompressible and compressible flows. Overset mesh technology is introduced aiming to analyze a flow around objects with complex motions. Hole-cutting process is realized using alternating digital tree (ADT) data structure and inclusion determination based on the X-rays algorithm. scFLOW's overset mesh technology can be coupled with physical functions such as free surface analysis, 6-DOF mechanism analysis and flow-structure interaction (FSI) analysis. The density-based scheme coupled with the overset mesh technology is especially effective for analyzing a moving object in a high-Mach number compressible flow. Numerical results of basic verification and engineering application are shown in this presentation.

[ presentation file (pdf) ] Tomohiro Irie

Speaker Bio: Tomohiro Irie is a group leader of Software Engineering Department at Software Cradle Co., Ltd. in charge scFlow solver development.

107th NIA CFD Seminar:

09-27-2018   11:00am-noon (EDT)   NIA Room 101      video

Solutions of Boundary Value and Periodic Problems for Flexible Multibody Dynamics Systems

Traditionally, the solution of flexible multibody dynamics problems is obtained via time marching. Many problems, however, are formulated as boundary value or periodic problems. The dynamic response of flexible multibody systems will be investigated via the finite element method, within the framework of the motion formalism, which leads to governing equations presenting low-order nonlinearities. Boundary value and periodic problems require global interpolation schemes that approximate the unknown motion fields over the system's entire period of response. The classical interpolation schemes developed for linear fields cannot be used for the nonlinear configuration manifolds, such as SO(3) or SE(3), that are used to describe the kinematics of multibody systems. Furthermore, the configuration and velocity fields are related through nonlinear kinematic compatibility equations.
It seems natural to implement the collocation version of the Fourier spectral method to determine periodic solutions of flexible multibody systems. Clearly, special procedures must be developed to adapt the Fourier spectral approach to flexible multibody systems. Assembly of the linearized governing equations at all the grid points leads to the governing equations of the spectral method. Numerical examples illustrate the performance of the proposed approach.
For periodic and boundary value problems, an approach based on the assembly of time- discretized elements provides an alternative approach to the problem. While it does not achieve the exponential convergence of Fourier spectral methods, it is computationally effective. The classical time integration schemes used in structural and multibody dynamics, such as the generalized-&alpha schemes, are not suitable for this approach. Time-discontinuous Galerkin schemes will be shown to be well suited for the solution of such problems.
The development of rigorous motion interpolation schemes also leads to interesting schemes for the spatial discretization of beam and shells. Spectral beam elements will be presented that are far simpler to implement than their counterparts based on the shape function used in classical finite element methods.

[ presentation file (pdf) ] Olivier A. Bauchau

Speaker Bio: Dr. Bauchau earned his B.S. degree in engineering at the Université de Ličge, Belgium, and M.S. and Ph.D. degrees from the Massachusetts Institute of Technology. He has been a faculty member of the Department of Mechanical Engineering, Aeronautical Engineering, and Mechanics at the Rensselaer Polytechnic Institute in Troy, New York (1983-1995), a faculty member of the Daniel Guggenheim School of Aerospace Engineering of the Georgia Institute of Technology in Atlanta, Georgia (1995-2010), a faculty member of the University of Michigan Shanghai Jiao Tong University Joint institute in Shanghai, China (2010-2015). He is now Igor Sikorsky Professor of Rotorcraft and Langley Professor at the Department of Aerospace Engineering at the University of Maryland.
His fields of expertise include finite element methods for structural and multibody dynamics, rotorcraft and wind turbine comprehensive analysis, and flexible multibody dynamics. He is a Fellow of the American Society of Mechanical Engineers, a Technical Fellow of the American Helicopter Society, and a Fellow of the American Institute of Aeronautics and Astronautics. His book entitled "Flexible Multibody Dynamics" has won the 2012 Textbook Excellence Award from the Text and Academic Authors Association. He is the 2015 recipient of the ASME d'Alembert award for lifelong contributions to the field of multibody system dynamics.

106th NIA CFD Seminar:

09-24-2018   11:00am-noon (EDT)   NIA Room 141      video

DNS of Roughness-Induced Transition in the Boundary Layer of a Hypersonic Spherical Forebody

The laminar-turbulent transition of the boundary layer on spherical forebodies at hypersonic speeds is a fundamental and yet not fully understood problem. Laminar-turbulent transition significantly impacts on skin friction and heat-transfer rates at the wall and, thus, its understanding is related to reliability and costs of re-entry vehicles.

Numerous experimental investigations have been conducted on capsule models with roughness in the last decades. However, further numerical investigations based on new computational methods are still needed. Compared to stability analysis (e.g. linear stability theory and parabolized stability equations), Direct Numerical Simulations allow for a more complete insight into non-linear instability mechanisms. Furthermore, as wind-tunnel experiments at realistic re-entry conditions matching all relevant dimensionless parameters, including the Damköhler number, are extremely difficult to realize, numerical simulations represent an important and often non-substitutable investigation tool.

In this talk, I will present the instability mechanisms in the boundary layer of a capsule-like geometry in the presence of a patch of (pseudo-)random distributed roughness. A set of different simulations are conducted for freestream conditions matching both wind-tunnel (Ma=6) and realistic re-entry (Ma=20) scenarios. In the case of re-entry conditions, the gradual inclusion of chemical and thermal non-equilibrium in the gas modeling will show the influence of the high temperature on the stability properties of the reacting boundary layer in the roughness wake.

[ presentation file (pdf) ] Antonio Di Giovanni

Speaker Bio: Antonio Di Giovanni is a PhD student at the Technical University of Munich, Germany. His research includes stability investigations on high-enthalpy hypersonic boundary layers. Current research projects comprehend studies of roughness-induced transition on capsule geometries and Görtler instabilities under consideration of non-equilibrium effects.

105th NIA CFD Seminar:

09-18-2018   11:00am-noon (EDT)   NIA Room 137      video

Three-Dimensional Prism-Dominant Mesh Generation for Viscous Flows Around Surface Slope Discontinuities

The NASA CFD Vision 2030 Study has identified mesh generation to be a significant bottleneck in the CFD pipeline. Human intervention is often required due to a lack of robustness and automation while generating the mesh. An automated approach to generating unstructured three-dimensional, prism-dominant meshes for viscous flows is presented. Meshes comprised of prisms are advantageous because they yield a more accurate solution and have fewer elements than their purely-tetrahedral mesh counterpart. An extrusion-based approach using multiple normals is used where anisotropic prisms are formed from the surface mesh facets and blend prisms are used to fill the cavities between multiple normals. Multiple normals are needed at a node to satisfy the visibility requirement for all incident surface facets. These multiple normals arise at regions of the surface mesh where there are convex discontinuities in the slope of the surface across edges. Nodes where blend region meshes must be formed are classified using an exhaustive enumeration scheme based on the number of convex edges and concave edges that are incident upon the node. Templates are presented to robustly mesh all the enumerated types of blend regions that occur at ridges, cusps, and corner nodes, including non-Lipschitz nodes. Intersections are detected in the boundary layer using an efficient spatial partitioning tree and are treated using Laplacian smoothing of the normal vectors or by reducing the total height of the boundary layer in the identified regions. The remainder of the volume is then tetrahedralized with an isotropic Delaunay mesh generator.

[ presentation file (pdf) ] Juliette Pardue

Speaker Bio: Juliette Pardue is a Ph.D. candidate in Computer Science at Old Dominion University under Dr. Andrey Chernikov and Dr. Nikos Chrisochoides. She is part of the Center for Real Time Computing, National Institute of Aerospace, and NASA Langley. Her research interests include mesh generation, parallel algorithms, computational fluid dynamics, and computational geometry. She has been published in the International Meshing Roundtable, the International Conference on Parallel Processing where her paper won the best paper award, the Virginia Modeling, Analysis, and Simulation Center Capstone Conference, and AIAA's Aviation Fluid Dynamics Conference. The first revision of her 2D distributed-memory parallel mesh generation work and code are currently under review by ACM's Transactions on Mathematical Software.

104th NIA CFD Seminar:

08-22-2018   11:00am-noon (EDT)   NIA Room 141      video

Sensitivity analysis of flexible multibody systems with application to rotor dynamics

The combination of analysis and optimization methods in mechanical engineering, also known as design optimization, has great potential in product development. In turn, robust sensitivity analyses that provide reliable and efficient objective function gradients play a key role in design optimization. This paper presents a discrete adjoint method for the sensitivity analysis of flexible mechanical systems. The ultimate goal is to be able to relate the physical properties of beam cross-sections to the dynamic behavior of the system, which is key to design realistic flexible elements. The underlying flexible multibody formulation is one that supports large-amplitude motion, beams with sophisticated composite cross-sections, and kinematic joints. A summary of the kinematic and dynamic foundations of the forward equations is presented first. Then, a discrete adjoint method, along with meaningful examples and validation, is presented. The method has proven to provide accurate and reliable sensitivities.

[ presentation file (pdf) ] Alfonso Callejo

Speaker Bio: Alfonso Callejo graduated in Industrial Engineering from the University of Navarra in 2008 and obtained a Master's Degree in Mechanical Engineering from the Technical University of Madrid in 2010. He obtained a Ph.D. in Mechanical Engineering at the University Institute for Automobile Research in 2013, entitled "Dynamic Response Optimization of Vehicles through Efficient Multibody Formulations and Automatic Differentiation Techniques". During his Ph.D., he conducted research at the Motion Research Group of the University of Waterloo. In 2013 he joined the National Institute for Aviation Research at Wichita State University. From 2014 to 2016 he was a Postdoctoral Fellow at McGill University's Centre for Intelligent Machines. Dr. Callejo is currently an Asst. Research Scientist at the University of Maryland. His research interests are in the areas of Efficient Multibody Formulations, Flexible Multibody Systems and Sensitivity Analysis.

103rd NIA CFD Seminar:

07-24-2018   11:00am-noon (EDT)   NIA Room 137      video

Study of High-Speed Transition due to Roughness Elements

Transitional hypersonic boundary layers due to diamond-shaped and cylindrical roughness elements (passive tripping) are studied using direct numerical simulations (DNS). A low Reynolds number experiment, consisting of an array of diamond-shaped roughness elements (Semper & Bowersox 2017), and a high Reynolds number experiment, consisting of an array of cylindrical roughness elements (Williams et al. 2018), are used to validate our simulations. Three dynamically prominent flow structures are consistently observed in both arrays as well as in their respective isolated roughness configurations. These flow structures are the upstream vortex system, the shock system, and the shear layers and the counter-rotating streamwise vortices from the wake of the roughness elements. Analysis of the power spectral density (PSD) reveals the dominant source of instability due to the diamond-shaped roughness elements as a coupled system of the shear layers and the counter-rotating streamwise vortices irrespective of spanwise roughness-spacing (isolated roughness and roughness-array). However, the dominant source of instability due to the cylindrical roughness elements is observed to be the upstream vortex system irrespective of spanwise roughness-spacing. Therefore, the shape of a roughness element plays an important role in the instability mechanism. Furthermore, dynamic mode decomposition (DMD) of three-dimensional snapshots of pressure fluctuations unveil globally dominant modes consistent with the PSD analysis in all the roughness configurations.

[ presentation file (pdf) ] Prakash Shrestha

Speaker Bio: Prakash Shrestha is a doctoral candidate in the Department of Aerospace Engineering and Mechanics at University of Minnesota-Twin Cities. Currently, he is working at National Institute of Aerospace (NIA) as a summer visiting student with Scott Berry, NASA Langley Research Center (LaRC), in high-speed transition due to wall-injectors. His research interests include boundary-layer stability, transition to turbulence, modal analysis, complex grid-generation, supersonics, and hypersonics.

102nd NIA CFD Seminar:

06-20-2018   11:00am-noon (EDT)   NIA Room 137      video

A GPU Accelerated Adjoint Solver for Shape Optimization

A graphics processing units (GPUs) accelerated adjoint-based optimization platform is proposed in this paper. Significant speed up gains and strong linear scalability of an existing in-house developed three-dimensional structured GPU Reynolds Averaged Navier-Stokes solver is presented first. As a first step towards the proposed GPU adjoint solver, a two-dimensional structured adjoint Euler solver is developed. The adjoint solver is further utilized to set up an airfoil shape optimization framework in Python and demonstrated for an airfoil shape optimization inverse problem. The two-dimensional adjoint Euler solver is extended to incorporate GPU acceleration using Compute Unified Device Architecture (CUDA) kernels and named ADjoint-GARfield (ADGAR). The adjoint optimization platform, ADGAR, is verified to a high accuracy of 14 significant digits with the serial adjoint Euler solver. Diagonalized Alternate Direction Implicit (DADI) iterative implicit schemes for both the forward and adjoint formulations are implemented and accelerated using CUDA kernels. The GPU accelerated structured code is finally successfully utilized to perform several airfoil shape optimizations for inverse design problems. Significant speedup up to 20x is observed using ADGAR for computations on a single GPU over a single CPU core.

[ presentation file (pdf) ] Asitav Mishra

Speaker Bio: Asitav Mishra is an Assistant Research Scientist in the Department of Aerospace Engineering at the University of Maryland as well as at the NIA since Oct 2017. His earlier research experiences include post-doctoral scholar positions at the University of Michigan (2015-2017) and the University of Wyoming (2012-2015) following his Ph.D in Aerospace Engineering from the University of Maryland in 2012. His research interests include adjoint based coupled multi-disciplinary fixed and rotary-wing design optimization, vortex wake-lifting surface interactions as well as performance predictions in rotary wing flows, and high performance computing using heterogenous GPU/CPU computing paradigms applied to CFD problems.

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