National Institute of Aerospace
Computational Fluid Dynamics Seminar

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

NIA CFD Seminar, Season 7 (2017-2018)
#103:   07-24-2018, Prakash Shrestha
Study of High-Speed Transition due to Roughness Elements
#102:   06-20-2018, Asitav Mishra
A GPU Accelerated Adjoint Solver for Shape Optimization
#101:   05-02-2018, Brody Bassett
Meshless Methods for the Neutron Transport Equation
#100:   04-10-2018, Hiroaki Nishikawa
Uses of Zero and Negative Volume Elements for Node-Centered Edge-Based Discretization
#99:   03-13-2018, Beckett Zhou
Aeroacoustic Optimization Capabilities in the Open-Source SU2 Solver
#98:   02-20-2018, Li Wang
High-fidelity Multidisciplinary Sensitivity Analysis and Design Optimization for Rotorcraft Applications
#97:   01-30-2018, Jialin Lou
Development and Implementation of Reconstructed Discontinuous Galerkin Methods for Computational Fluid Dynamics on GPUs
#96:   11-28-2017, Yong Su Jung
Hamiltonian-Strand (HAMSTR) Approach Using Hybrid Meshes for Aerodynamic Flow Analysis
#95:   10-16-2017, James D. Baeder
A Personal Journey Towards High Fidelity Rotorcraft CFD
#94:   09-28-2017, Olivier A. Bauchau
Flexible Multibody Dynamics Tools For Rotorcraft Comprehensive Analysis
#93:   09-19-2017, Yi Liu
Third-Order Edge-Based Hyperbolic Navier-Stokes Scheme for Three-Dimensional Viscous Flows
#92:   08-18-2017, Keiichi Kitamura
SLAU2 and Post Limiter for (Unlimited) Second-Order Flow Simulations on Unstructured Grids

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.

101st NIA CFD Seminar:

05-02-2018   10:00am-11:00am (EST)   NIA Room 137      video

Meshless Methods for the Neutron Transport Equation

Mesh-based methods for the numerical solution of partial differential equations (PDEs) require the division of the problem domain into non-overlapping, contiguous subdomains that conform to the problem geometry. The mesh constrains the placement and connectivity of the solution nodes over which the PDE is solved. In meshless methods, the solution nodes are independent of the problem geometry and do not require a mesh to determine connectivity. This allows the solution of PDEs on geometries that would be difficult to represent using even unstructured meshes. The ability to represent difficult geometries and place solution nodes independent of a mesh motivates the use of meshless methods for the neutron transport equation, which often includes spatially-dependent PDE coefficients and strong localized gradients. The meshless local Petrov-Galerkin (MLPG) method is applied to the steady-state and k-eigenvalue neutron transport equations, which are discretized in energy using the multigroup approximation and in angle using the discrete ordinates approximation. The MLPG method uses weighted residuals of the transport equation to solve for basis function expansion coefficients of the neutron angular flux. Connectivity of the solution nodes is determined by the shared support domain of overlapping meshless functions, such as radial basis functions (RBFs) and moving least squares (MLS) functions.

To prevent oscillations in the neutron flux, the MLPG transport equations are stabilized by the streamline-upwind Petrov-Galerkin (SUPG) method, which adds numerical diffusion to the streaming term. Global neutron conservation is enforced by using MLS basis and weight functions and appropriate SUPG parameters. The cross sections in the transport equation are approximated in accordance with global particle balance and without constraint on their spatial dependence or the location of the basis and weight functions. The equations for the strong-form meshless collocation approach are derived for comparison to the MLPG equations. Two integration schemes for the basis and weight functions in the MLPG method are presented, including a background mesh integration and a fully meshless integration approach. The method of manufactured solutions (MMS) is used to verify the resulting MLPG method in one, two and three dimensions. Results for realistic problems, including two-dimensional pincells, a reflected ellipsoid and a three-dimensional problem with voids, are verified by comparison to Monte Carlo simulations. Finally, meshless heat transfer equations are derived using a similar MLPG approach and verified using the MMS. These heat equations are coupled to the MLPG neutron transport equations and results for the power coefficient of reactivity are compared to values from a commercial pressurized water reactor.

[ presentation file (pdf) ] Brody Bassett

Speaker Bio: Brody Bassett received his BS in Physics from Brigham Young University and his MS in Nuclear Engineering from Oregon State University. He is currently working on his PhD in Nuclear Engineering and Radiological Sciences at the University of Michigan, where his dissertation is focused on the application of meshless methods to the neutron transport equation.

100th NIA CFD Seminar:

04-10-2018   11:00am-noon (EST)   NIA Room 101      video

Uses of Zero and Negative Volume Elements for Node-Centered Edge-Based Discretization

This talk will discuss how zero and negative volume elements can be useful in Computational Fluid Dynamics (CFD) simulations: third-order accuracy on grids with inverted triangles, singularities better resolved with zero volume elements, zero-width shock capturing, local refinement of quadrilateral grids without hanging nodes, overset grids made a single grid for a drastic simplification in algorithms and for trivial satisfaction of discrete conservation. All practical CFD codes in the world today consider grids with zero/negative volumes as invalid or failure, and thus simulations are never performed on such grids. This work opens the door to a new era in CFD: improved simulations via hitherto-impossible computational grids.

[ presentation file (pdf) ] Hiro Nishikawa

Speaker Bio: Dr. Hiro Nishikawa is Associate Research Fellow, NIA. He earned Ph.D. in Aerospace Engineering and Scientific Computing at the University of Michigan in 2001. He then worked as a postdoctoral fellow at the University of Michigan on adaptive grid methods, local preconditioning methods, multigrid methods, rotated-hybrid Riemann solvers, high-order upwind and viscous schemes, and joined NIA in 2007. His area of expertise is the algorithm development for CFD, focusing on the hyperbolic method for diffusion, and derived methods for robust, efficient, highly accurate viscous discretization schemes on unstructured grids.

Relevant Publications: AIAA Computational Fluid Dynamics Conference Best Paper 2017
H. Nishikawa, "Uses of Zero and Negative Volume Elements for Node-Centered Edge-Based Discretization", AIAA Paper 2017-4295, 23rd AIAA Computational Fluid Dynamics Conference, 5 - 9 June 2017, Denver, Colorado.
[ bib | pdf | ARC ]

99th NIA CFD Seminar:

03-13-2018   11am-noon (EST)   NIA Room 137      video

Aeroacoustic Optimization Capabilities in the Open-Source SU2 Solver

A hybrid noise prediction framework is developed for the open-source SU2 solver suite, in which a permeable surface Ffowcs Williams and Hawkings (FW-H) Equation solver is implemented and coupled with an unsteady Reynolds-averaged Navier-Stokes (URANS) solver. The accuracy of this hybrid framework is verified using a number of canonical test cases. A discrete adjoint solver based on algorithmic differentiation (AD) is developed for the coupled system which directly inherits the convergence properties of the primal flow solver due to the differentiation of the entire nonlinear fixed-point iterator. This framework is applied to 2-D and 3-D noise minimization cases via shape optimization. The lift and noise design objectives were shown to be competing in all cases studied -- noise minimization always leads to a marked loss of lift. Lift-constrained noise minimization were performed for all 2-D cases and shown to be able to successfully constrain the mean lift at its baseline level while still reducing noise. A number of unconventional optimal designs were obtained, including airfoil designs with wavy surfaces to reduce wake interaction noise. In the 3-D case, the baseline and optimized designs were also analyzed using a turbulence-resolving delayed detached-eddy simulation (DDES). The results indicate that the tonal noise reduction attained by URANS-FWH-based noise minimization is consistent with the higher-fidelity DDES-FWH noise prediction results.

[ presentation file (pdf) ] Beckett Zhou

Speaker Bio: Beckett Zhou is a Research Scholar at the National Institute of Aerospace. He is currently working with Len Lopes (NASA Langley) and Justin Gray (NASA Glenn) in coupling the SU2 solver with the ANOPP2 and OpenMDAO programs to perform propeller noise minimization. He performed doctoral research on adjoint-based aeroacoustic optimization at the RWTH Aachen University in Germany under the supervision of Professors Nicolas Gauger and Wolfgang Schröder from 2012 to 2017, and will defend his PhD thesis in April 2018. Since 2015, he has led the development of the aeroacoustics branch of the SU2 Solver. His primary research interests are: adjoint-based design optimization, computational aeroacoustics and hybrid RANS/LES methods. He received a Masters in Aeronautics and Astronautics from MIT in 2012, and a Bachelor of Applied Science from the University of Toronto in 2010.

98th NIA CFD Seminar:

02-20-2018   11am-noon (EST)   NIA Room 137      video

High-fidelity Multidisciplinary Sensitivity Analysis and Design Optimization for Rotorcraft Applications

This talk will present a multidisciplinary sensitivity analysis approach that has been developed and applied to rotorcraft simulations involving tightly coupled high-fidelity computational fluid dynamics and comprehensive analysis. An unstructured-grid, highly-scalable CFD solver and a nonlinear flexible multibody dynamics model are coupled to predict aerodynamic loads and structural responses of helicopter rotor blades. A discretely-consistent, adjoint-based sensitivity analysis in the fluid dynamics solver provides sensitivities arising from unsteady turbulent flows on unstructured, dynamic, overset meshes, while a complex-variable approach is used to assess structural sensitivities with respect to aerodynamic loads. The multidisciplinary sensitivity analysis is conducted through integrating the sensitivity components from each discipline of the coupled system. Accuracy of the coupled system for high-fidelity rotorcraft analysis is verified; simulation results exhibit good agreement with established solutions. A constrained gradient-based design optimization for a HART-II rotorcraft configuration is demonstrated. The computational cost for individual components of the multidisciplinary sensitivity analysis is assessed and improved.

[ presentation file (pdf) ] Li Wang

Speaker Bio: Dr. Li Wang is a Senior Research Engineer from the National Institute of Aerospace. Her current work focuses on development of a practical, efficient, and high-fidelity tool for multidisciplinary sensitivity analysis involving coupled computational fluid dynamics and comprehensive analysis for rotorcraft aeromechanics. Li earned her PhD degree in Mechanical Engineering at the University of Wyoming in 2009. Her PhD research was centered on development of techniques for high-order adaptive discontinues Galerkin methods in fluid dynamics. Prior to joining NIA, Li held an Assistant Research Professor position in 2009-2015 at the SimCenter of University of Tennessee, Chattanooga, and a joint appointment with the Oak Ridge National Laboratory, where she gained extensive experiences on high-order computational fluid dynamics methods for turbulent flow simulations, adjoint-based error estimation, and aerodynamic shape design optimization. Dr. Wang served as a member of the AIAA Applied Aerodynamics Technical Committee in 2011-2017 and Technical Co-chair of the 31st AIAA Applied Aerodynamics Conference.

97th NIA CFD Seminar:

01-30-2018   11am-noon (EST)   NIA Room 137      video

Development and Implementation of Reconstructed Discontinuous Galerkin Methods for Computational Fluid Dynamics on GPUs

The objective of the effort presented in this work is to port an unstructured CFD solver, reconstructed discontinuous Galerkin flow solver (RDGFLO), onto GPU platform using OpenACC. The solver is based on a third-order hierarchical Weighted Essentially Non-Oscillatory (WENO) reconstructed DG methods. By taking advantages of the OpenACC parallel programming model, the presented scheme requires the minimum code intrusion and algorithm alteration to upgrade a legacy CFD solver without much extra time and effort in programming, resulting in a unified portable code for both CPU and GPU platforms. A number of inviscid and viscous flow problems are presented to verify the implementation of the developed schemes on the GPU. Strong scaling tests are carried out to compare the unit running time on single GPU and single CPU to obtain the speedup factor of the developed methods. Also, weak scaling tests are used for several cases to test the parallel efficiency for multi-GPU computing by comparing the unit running time with different number of GPU cards for an approximately fixed problem size per GPU card. The results of timing measurements indicate that this OpenACC-based parallel scheme is able to significantly accelerate the solving procedure for the equivalent legacy CPU code.

[ presentation file (pdf) can play movies in Acrobat Reader ] Jialin Lou

Speaker Bio: Dr. Jialin Lou earned his B.S. degree in Engineering Mechanics at Beijing Institute of Technology and M.S. and Ph.D. degree from North Carolina State University under Dr. Hong Luo's advice. He recently joined Old Dominion University Research Foundation as a post-doctoral research associate, working with Dr. Nail Yamaleev in Mathematics and Statistics Department. His research interest lies in high order numerical methods, hyperbolic diffusion schemes, and High Performance Computer (HPC) parallel computing in both CPU and GPU platforms.

96th NIA CFD Seminar:

11-28-2017   11am-noon (EST)   NIA Room 101      video

Hamiltonian-Strand (HAMSTR) Approach Using Hybrid Meshes for Aerodynamic Flow Analysis

A solution framework using Hamiltonian paths and strand grids (HAMSTR) is presented for two and three-dimensional flows. The methodology can create a volume mesh starting from either an unstructured surface mesh comprised of mixed triangular-quadrilateral elements or a fully unstructured volume mesh. "Line structure" through the meshes are found in a robust manner and the flow solver uses line-implicit schemes and stencil-based discretization along these lines, similar to a structured grid flow solver. The framework has been developed mostly for rotorcraft CFD simulations, which requires robust mesh generation around complex geometry and efficient numerical method for large scale problems. HAMSTR is a 3D compressible finite volume solver that can operate across multiple processors using MPI. Hybrid RANS/LES turbulence modeling based on the Spalart-Allmaras turbulence model and Y-[Re]θ-SA laminar/turbulent transition model of Medida-Baeder are integrated into the solver for better predictions of the boundary layer and resulting flowfield as compared with a fully turbulent RANS simulation. Furthermore, deformable meshes can also be handled for elastic body simulations such as rotor blades. An overset technique (using TIOGA) allows for a hybrid mesh system, which consists of a near-body Hamiltonian/Strand grid and off-body Cartesian nested meshes. The integration framework between the various components of the code is performed using Python to allow for ease of integration to other codes in the research group. The current infrastructure is used to explore various cases ranging from simple representative geometries, such as 2D airfoil, to complex geometries such as rotating rotor hub and a full wind turbine. Some, CFD/CSD predictions for a slowed rotor are also studied.

[ presentation file (pdf) ] Yong Su Jung

Speaker Bio: Yong Su Jung is a Ph.D candidate student in Aerospace Engineering department at the University of Maryland. He holds B.S (2012). and M.S (2014) in Aerospace Engineering from Korea Advanced Institute of Science and Technology. His research interests are in developing and applying Computational Fluid Dynamics methods for external flow simulations, such as rotary wing. His research has been funded by Department of Defense (DoD) HPCMP CREATE-AV program and Korea Aerospace Research Institute. He was a member of the University Maryland team received first place in the graduate category for 2016 AHS Design Competition.

95th NIA CFD Seminar:

10-16-2017   1pm-2pm (EST)   NIA Room 101      video

A Personal Journey Towards High Fidelity Rotorcraft CFD

In the 1980's it was sufficient for CFD to look at very simplified model rotorcraft problems, for example: a 2-D airfoil encountering an isolated prescribed vortex or a non-lifting isolated rotor blade in forward flight generating unsteady shock waves. In most instances the inviscid Euler equations were used or else the flow was assumed to be fully turbulent and an algebraic turbulence model was used for closure. While relatively unsophisticated by today's standards, they were able to provide some key physical insights into such phenomena as blade-vortex interactions and high-speed impulsive noise. It also served to pique interest in the rotorcraft community as to how CFD could be applied to practical problems. High fidelity rotorcraft aerodynamic simulations are inherently multi-disciplinary and require hybrid methods to resolve all relevant fluid scales. Thus, applications of computational fluid dynamics to rotorcraft over the past 25 years have required an increase in the level of sophistication not only of the included physics but also of more complicated configurations with more complex geometries. As a result this has necessitated not only increased computer hardware, but also the development of more sophisticated algorithms. The first part of this seminar will discuss the wide range of improvements made to rotorcraft CFD simulations at the Alfred Gessow Rotorcraft Center over the past 20+ years. In regards to multi-disciplinary physics this includes such areas as: aeroacoustics, structural coupling and trim, low Reynolds number and low Mach number flows, laminar/turbulent transition, two-phase flow (particles in fluids), and the capturing of tip vortices and other large eddies. These have been accompanied by algorithmic improvements that have included: hybrid Eulerian/Lagrangian methods for wake coupling, vortex tracking grids, compact reconstruction of inviscid fluxes, hybrid RANS/LES turbulence modeling, and GPGPU programming. More complicated geometries have been enabled through: implicit hole-cutting for overset meshes, simplified models for flaps and other actuators, and the use of unstructured meshes. The second part of the seminar will focus on the application of uncertainty quantification to look at the effect of uncertainty in free-stream turbulence intensity levels on 2-D airfoil integrated forces and moments as well as flow physics.

[ presentation file (pdf) ] James D. Baeder

Speaker Bio: Dr. James D. Baeder is a member of the Alfred Gessow Rotorcraft Center as Professor in Aerospace Engineering at the University of Maryland; he is currently the Associate Langley Professor Chair at the National Institute for Aerospace. He holds a B.S. in Mechanical Engineering from Rice University and M.S. and Ph.D. in Aeronautics and Astronautics from Stanford University. He joined the AGRC in 1993 after nine years at AFDD. His research interests are in developing and applying Computational Fluid Dynamic methods to better understand and predict rotary and flapping wing aerodynamics, acoustics and dynamics. One of his key research thrusts is the development of multi-fidelity coupled CFD/ free-wake/ structural dynamics/ acoustic methods. His pioneering efforts in predicting high-speed vibration and noise of helicopters, together with Dr. Chopra, are leading to a better understanding of the physical mechanisms responsible for the large increase in vibrations at such conditions. Additional applications include simulating: the use of active elements; helicopter "brownout"; interactional aerodynamics; aerodynamic performance and flow-field of small-scale rotary and flapping UAV; vertical axis wind turbines (VAWT); and offshore wind turbines. Currently he is pioneering the development of improved CFD algorithms, with a focus on GPGPU technology, to: capture the details of laminar/turbulent transition; dynamic stall; as well as tip vortex formation, convection and interaction with other surfaces including fuselages, towers or the ground and including adjoint capabilities. Dr. Baeder's research has been funded by Excelon, NASA Ames and Langley, the Army Aeroflightdynamics Directorate, the Army Research Office, the National Rotorcraft Technology Center, NAVAIR and DARPA, with support from the various helicopter companies. He has authored more than 45 archival journal articles. He received the 1993 Schroers Award for Outstanding Rotorcraft Research from the San Francisco Bay Area Chapter of the AHS and the 2010 AIAA National Capital Section Engineer of the Year Award. He advised the University of Maryland team to receive First Place in the Undergraduate Category of the 2017 American Helicopter Design Competition. Dr. Baeder is an Associate Fellow of AIAA and a member of AHS. He currently chairs the Innovation and Commercialization Committee of the Business Network for Offshore Wind as well as the National Offshore Wind Innovation Center.

94th NIA CFD Seminar:

09-28-2017   12 pm-1pm (EST)   NIA Room 137      video

Flexible Multibody Dynamics Tools For Rotorcraft Comprehensive Analysis

Flexible multibody dynamics techniques provide a framework for the dynamic analysis of aerospace vehicles in general and of rotorcraft, in particular. Dymore is a flexible multibody dynamics code that includes geometrically-exact beam elements, rigid bodies, kinematic joints, and modal elements. Through an integrated set of interface routines, Dymore enables the use of simple aerodynamic models but also allows the coupling of structural dynamics models with advanced CFD tools such as FUN3D or OVERFLOW. SectionBuilder is a finite element based tool that evaluates exact solutions of three-dimensional elasticity for beams of general cross-sectional shape made of anisotropic materials; the three-dimensional stress field at any point of the blade is a byproduct of these exact solutions. Rotor blade detailed design, structural integrity, fatigue life, and optimization all depend on the accurate knowledge of three-dimensional stress distributions.

Recently, a parallel version of Dymore has been developed by integrating three key techniques: (1) the motion formalism, which removes most kinematic nonlinearities from the governing equations of motion, (2) domain decomposition techniques that partition the system to exploit the reduced nonlinearities and (3) parallel computation is then a natural consequence of the independence of the sub- domains. Ongoing and future developments of Dymore and SectionBuilder will be presented; they include (1) the development of spectral solvers for the evaluation of periodic solutions for flexible multibody systems, (2) the development of discretely consistent adjoint-based sensitivity analysis, and (3) the development of nonlinear three-dimensional finite element modeling of rotorcraft structures based on the motion formalism.

[ presentation file (pdf) ] Olivier A. Bauchau

Speaker Bio: Dr. Bauchau earned his B.S. degree in engineering at the Université de Liège, 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 in 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 senior member 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.

93rd NIA CFD Seminar:

09-19-2017   11:00am-noon (EST)   NIA Room 101      video

Third-Order Edge-Based Hyperbolic Navier-Stokes Scheme for Three-Dimensional Viscous Flows

We present a third-order edge-based scheme for the three-dimensional Navier-Stokes equations. The node-centered edge-based scheme achieves third-order accuracy on tetrahedral grids with quadratic least-squares gradients and linear flux reconstruction for the Euler equations. It is extended to the viscous terms by the hyperbolic Navier-Stokes method, in which the viscous terms are written as a first-order hyperbolic system with source terms. The source terms introduced by the hyperbolic formulation are discretized by a new quadrature formula recently discovered, which does not require second derivatives. Third-order accuracy is demonstrated not only for the solution variables but also for their gradients on fully irregular grids. The developed scheme is implemented in NASA's FUN3D code, and tested for three-dimensional laminar flow problems. The seminar concludes with a brief discussion on future work towards third-order turbulent-flow computations on unstructured grids.

[ presentation file (pdf) ] Yi Liu

Speaker Bio: Dr. Yi Liu graduated from Georgia Institute of Technology with a Ph.D degree in aerospace engineering in 2003. He also holds a M.E. from Beijing University of Aeronautics and Astronautics in Beijing, China. In 2004, he joined the National Institute of Aerospace after a one-year postdoctoral fellowship at Georgia Tech. He has previously served as a senior research engineer at NIA in the area of computational fluid dynamics (CFD) and multi-disciplinary analysis of rotorcraft configurations. He has conducted various research projects, including work in the areas of rotorcraft aerodynamic analysis and acoustic prediction; micro-air vehicle and flapping wing aerodynamics sponsored by ARL and NASA. Currently, he is conducting the research project of implementation of third-order edge-based scheme in NASA CFD solver FUN3D with collaboration of researchers at NASA LaRC-Computational AeroSciences Branch.

92nd NIA CFD Seminar:

08-18-2017   11:00am-noon (EST)   NIA Room 137      video

SLAU2 and Post Limiter for (Unlimited) Second-Order Flow Simulations on Unstructured Grids

This talk will present two methods: SLAU2 flux function and "Post Limiter." SLAU2 is robust against shockwave-induced anomalous solutions at hypersonic speeds ("carbuncle" phenomena), while it can be used at low speeds e.g., Mach 0.001 - thus, designated as an all-speed scheme. SLAU2, with its predecessor SLAU, has been incorporated into JAXA's CFD code "FaSTAR", and widely used by many researchers and practitioners in- and outside Japan. The present talk will focus on its very recent extension to supercritical fluids, in which an energy equation to be solved was replaced by its mathematically-equivalent, pressure-evolution equation, to suppress numerical oscillations.

"Post Limiter (simple a posteriori slope limiter)" is a means to deactivate a conventional slope limiter as much as possible (even at shocks), unless it is truly needed. In other words, "unlimited" slopes are favored rather than the limited ones by the slope limiter at all the cell-interfaces. As a result, dramatic improvements of both flow resolution (four times in each dimension) and convergence have been observed. This approach is powerful especially when a spatially second-order reconstruction is performed and grid points are clustered to physics-rich regions on unstructured grids, such as in FaSTAR.

[ presentation file (pdf) ] Keiichi Kitamura

Speaker Bio: Dr. Keiichi Kitamura was an exchange student at University of Michigan, Ann Arbor (2007), and received Dr. of Engineering from Nagoya University, Japan (2008). Then he experienced Postdoctoral Researcher at JAXA (2008-2011) and NASA Glenn (2011-2012), Assistant Prof. at Nagoya University (2012-2014), and became Associate Prof. at Yokohama National University, Japan (2014). He has proposed several numerical flux functions such as SLAU2 (2013), and also a new limiting strategy called "Post Limiter" (2017) to turn off a slope limiter at unnecessary places.

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