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NIA CFD Seminar, Season 5 (2015-2016)
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#76: 05-18-2016, Alireza Mazaheri
High-Order Discontinuous-Galerkin Schemes using Hyperbolic First-Order System Approach: same DoF as conventional but more accurate
#75: 05-04-2016, Heng Xiao
A Data-Driven, Physics-Informed Approach towards Predictive Turbulence Modeling
#74: 03-24-2016, Xiangmin (Jim) Jiao
Robust Adaptive High-Order Geometric and Numerical Methods Based on Weighted Least Squares
#73: 03-23-2016, Ke Shi
Superconvergent HDG Methods on General Polyhedral/Polygonal Meshes
#72: 03-08-2016, James M. Chen
A Kinetic Description of Morphing Continuum Theory and its Applications
#71: 02-24-2016, Alireza Mazaheri
Hyperbolic Method for Dispersive PDEs: Same High-Order of Accuracy for Solution, Gradient, and Hessian
#70: 02-10-2016, Ali Uzun
Wall-Resolved Large Eddy Simulations of Separated Flows
#69: 01-26-2016, Alireza Mazaheri
High-Order Residual-Distribution Schemes for Discontinuous Problems on Irregular Triangular Grids
#68: 11-19-2015, Olivier A. Bauchau
Integrating Three-Dimensional Stress Evaluation With Rotorcraft Comprehensive Analysis
#67: 11-03-2015, Prahladh S. Iyer
High-Speed Boundary-Layer Transition Induced by a Discrete Roughness Element
#66: 10-27-2015, Eric Loth
Observation of Novel Dynamics for a Low-Boom Relaxed-Compression Supersonic Inlet
#65: 10-20-2015, Pedro Paredes
Advances in Global Instability Computations: from Incompressible to Hypersonic flows
#64: 09-29-2015, Hiro Nishikawa
Third-Order Edge-Based Scheme and New Hyperbolic Navier-Stokes System
#63: 09-15-2015, Ali Uzun
High-Fidelity Simulations of Complex High-Speed Flows
#62: 09-08-2015, Alireza Mazaheri
Is Curved-Element a Necessity for all High-Order Schemes?
#61: 08-26-2015, Hiro Nishikawa
Third-Order Active Flux Schemes for Advection Diffusion
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05-18-2016
11:00am-noon (EST)
NIA Room 137
 video
High-Order Discontinuous-Galerkin Schemes using Hyperbolic First-Order System Approach: same DoF as conventional but more accurate
We propose arbitrary high-order discontinuous Galerkin (DG) schemes that are designed based on a first-order hyperbolic advection-diffusion formulation of the target governing equations. We present, in details, the efficient construction of the proposed high-order schemes (called DG-H), and show that these schemes have the same number of global degrees-of-freedom as comparable conventional high-order DG schemes, produce the same or higher order of accuracy solutions and solution gradients, are exact for exact polynomial functions, and do not need a second-derivative diffusion operator. We also present construction of a Weighted Essentially Non-Oscillatory (WENO) limiter for the proposed DG-H schemes. We demonstrate that the constructed high-order schemes give excellent quality solution and solution gradients on irregular triangular elements. Finally, we make some comparisons with conventional DG and interior-penalty schemes.
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presentation file (pdf)
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Alireza Mazaheri |
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Speaker Bio:
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Dr. Alireza Mazaheri is a Computational Aerothermodynamicist at NASA Langley Research center since 2006. Prior to his current NASA civil servant position, he was a NASA contractor at the Analytical Mechanics Associates, Inc., a research engineer at Parsons Inc., a postdoctoral fellow at Pittsburgh University, and a National Research Council (NRC) postdoctoral fellow at the US Department of Energy. He earned his PhD from Clarkson University in Mechanical Engineering, MS from Shiraz University in Computational Thermo-Fluid Engineering, and BS from Guilan University in Fluid Mechanics. Dr. Mazaheri has been involved in several NASA programs/projects, including the Space Shuttle, Orion Multi Purpose Crew Vehicle (MPCV), Dream Chaser, Hypersonic Inflatable Aerodynamic Decelerator (HIAD), High Energy Atmospheric Reentry Test (HEART), etc. He is the author of the flight boundary layer transition and the 3D radiation ray-tracing codes, and has been a member of the LAURA-5 development team, and collaborated in the development of the coupled-ablation capability in Fun3D. His current research is on the development of high-order methods for irregular simplex elements with emphasis on solution gradients (e.g., velocity gradients, heat flux, shear stresses, etc.).
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05-04-2016
11:00am-noon (EST)
NIA Room 137
video
A Data-Driven, Physics-Informed Approach towards Predictive Turbulence Modeling
Despite their well-known limitations, Reynolds-Averaged Navier-Stokes (RANS) models are still the workhorse tools for engineering turbulent flow simulations. In this talk we present a data-driven, physics-informed approach for quantifying and reducing model-form uncertainties in RANS simulations. The framework utilizes an ensemble-based Bayesian inference method to incorporate all sources of available information, including empirical prior knowledge, physical constraints (e.g., realizability, smoothness, and symmetric), and available observation data [1-2]. When there are no available data on the flow to be predicted, we showed that the Reynolds stress discrepancy can be calibrated on related flows where data are available [3]. This finding has profound physical and modeling implications, i.e., the errors in RANS modeled Reynolds stresses are not random, but can be well explained by the mean flow features. This work demonstrates the potential of the data-driven predictive turbulence modeling approach based on standard RANS models, which is an alternative to advanced RANS models.
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Speaker Bio:
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Dr. Heng Xiao is an Assistant Professor in the Department of Aerospace and Ocean Engineering at Virginia Tech. He holds a bachelor's degree in Civil Engineering from Zhejiang University, China, a master's degree in Mathematics from the Royal Institute of Technology (KTH), Sweden, and a Ph.D. degree in Civil Engineering from Princeton University, USA. Before joining Virginia Tech in 2013, he worked as a postdoctoral researcher at the Institute of Fluid Dynamics in ETH Zurich, Switzerland, from 2009 to 2012. His current research interests lie in model uncertainty quantification in turbulent flow simulations. He is also interested in developing novel algorithms for high-fidelity simulations of particle-laden flows with application to sediment transport problems.
More information can be found in the manuscripts below or from the presenter's website:
https://sites.google.com/a/vt.edu/hengxiao/papers
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Relevant Publication:
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[1]. H. Xiao, J.-L. Wu, J.-X. Wang, R. Sun, and C. J. Roy. Quantifying and reducing model-form uncertainties in Reynolds averaged Navier-Stokes equations: An open-box, physics-based, Bayesian approach. Submitted to JCP, 2015. Also available at
arxiv:1508.06315
[2]. J.-X. Wang, J.-L. Wu, and H. Xiao. Incorporating prior knowledge for quantifying and reducing model-form uncertainty in RANS simulations. Submitted to IJUQ, 2015. Also available at
arxiv:1512.01750
[3]. J.-L. Wu, J.-X. Wang, and H. Xiao. A Bayesian calibration-prediction method for reducing model-form uncertainties with application in RANS simulations. Flow, Turbulence and Combustion, 2016. In press.
DOI: 10.1007/s10494-016-9725-6 Also available at
arxiv: 1510.06040
[4]. H. Xiao, J. X. Wang and Roger G. Gahnem. A Random Matrix Approach for Quantifying Model-Form Uncertainties in Turbulence Modeling. Submitted to CMAME, 2016. Available at
arxiv:1603.09656
[5]. J. X. Wang, R. Sun, H. Xiao. Quantification of Uncertainty in RANS Models: A Comparison of Physics-Based and Random Matrix Theoretic Approaches. Submitted, 2016. Available at
arxiv:1603.05549
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03-24-2016
2:00pm-3:00pm (EST)
NIA Room 137
video
Robust Adaptive High-Order Geometric and Numerical Methods Based on Weighted Least Squares
Numerical solutions of partial differential equations (PDEs) are important for modeling and simulations in many scientific and engineering applications. Their solutions over com- plex geometries pose significant challenges in efficient surface and volume mesh generation and robust numerical discretizations. In this talk, we present our recent work in tackling these challenges from two aspects. First, we will present accurate and robust high-order geomet- ric algorithms on discrete surface, to support high-order surface reconstruction, surface mesh generation and adaptation, and computation of differential geometric operators, without the need to access the CAD models. Secondly, we present some new numerical discretization tech- niques, including a generalized finite element method based on adaptive extended stencils, and a novel essentially nonoscillatory scheme for hyperbolic conservation laws on unstructured meshes. These new discretizations are more tolerant of mesh quality and allow accurate, stable and efficient computations even on meshes with poorly shaped elements. Based on a unified theoretical framework of weighted least squares, these techniques can significantly simplify the mesh generation processes, especially on supercomputers, and also enable more efficient and robust numerical computations. We will present the theoretical foundation of our methods and demonstrate their applications for mesh generation and numerical solutions of PDEs.
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Speaker Bio:
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Dr. Xiangmin (Jim) Jiao is an Associated Professor in Applied Mathematics and Computer Science, and also a core faculty member of the Institute for Advanced Computational Science at Stony Brook University. He received his Ph.D. in Computer Science in 2001 from University of Illinois at Urbana-Champaign (UIUC). He was a Research Scientist at the Center for Simulation of Advanced Rockets (CSAR) at UIUC between 2001 and 2005, and then an Assistant Professor in College of Computing at Georgia Institute of Technology between 2005 and 2007. His research interests focus on high-performance geometric and numerical computing, including applied computational and differential geometry, generalized finite difference and finite element methods, multigrid and iterative methods for sparse linear systems, multiphysics coupling, and problem solving environments, with applications in computational fluid dynamics, structural mechanics, biomedical engineering, climate modeling, etc.
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03-23-2016
11:00am - noon (EST)
NIA Room 137
video
Superconvergent HDG Methods on General Polyhedral/Polygonal Meshes
The hybridizable DG methods (HDG) was first introduced by Cockburn et al. in 2009. Since then it has been extensively developed by many colleagues in this area. It has gained lots of attention due to its unique features comparing with conventional methods (CG, DG, mixed methods etc). Roughly speaking, HDG methods . do share with mixed methods their superior convergence properties and can be implemented as efficiently as the hybridized mixed methods while retaining the advantages typical of the DG methods. In this talk, we will discuss a new class of HDG methods for many linear and nonlinear problems. A main feature of this approach is that the method provides optimal approximations for all unknowns on general polyhedral/polygonal meshes.
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Speaker Bio:
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Dr. Shi got his PhD at the University of Minnesota supervised by Bernardo Cockburn, in 2012. He spent three years at the Texas A&M University as a visiting assistant professor. In 2016, he joined the department of Mathematics and Statistics of the Old Dominion University. His research covers a wide range of interests in numerical analysis and scientific computing, with a focus on hybridizable DG methods, multiscale finite element methods for flow problems in heterogeneous media.
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03-08-2016
11:00am - noon (EST)
NIA Room 141
video
A Kinetic Description of Morphing Continuum Theory and its Applications
The coupling between the intrinsic angular momentum and the hydrodynamic linear momentum has been known to be prominent in fluid flows involving physics across multiple length and time scales, e.g. turbulence, hypersonic rarefied flow and flows at micro-/nano-scale. The classical Navier-Stokes (N-S) equations can only correctly predict the decay of the transverse velocity autocorrelation down to few atomic diameters. Morphing Continuum (MCT, Micropolar) Theory (Eringen, 1964; Chen et. al., 2011) is mathematically formulated under the framework of continuum thermomechanics to account for the decay correlation at smaller wavelength. The mathematically rigorous continuum thermomechanics introduce new material constants into the MCT governing equations, but leave their physical meanings unexplained. Similar to Boltzmann's kinetic theory explaining the viscosity in the N-S equations, I will discuss an advanced kinetic theory, including a newly derived Boltzmann-Curtiss (B-C) distribution function and the B-C equations for polyatomic gases. I will demonstrate that the corresponding B-C equations are the MCT governing equations without any dissipation terms when the system of polyatomic gases is in equilibrium, i.e. under B-C distribution. Preliminary results using MCT for (1) the transition and turbulent flow triggering by the wall-bounded disturbances, and (2) the shock wave/wall-bounded disturbances interactions for supersonic flow with Ma = 3.
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Speaker Bio:
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Dr. James M. Chen earned his B.S. in mechanical engineering at National Chung-Hsing University (2000), Taiwan, M.S. in applied mechanics at National Taiwan University (2005) and Ph.D. in mechanical and aerospace engineering and applied mathematics (minor) at The George Washington University (2011). He joined Kansas State University as an Assistant Professor of mechanical engineering at Kansas State University in Fall 2015. Prior to joining K-State, he was a faculty in engineering at Penn State Altoona (2012-2015). He has published more than 30 peer-reviewed journal articles/book chapters in multiscale computational mechanics, theoretical & computational fluid dynamics and atomistic simulation for thermo-electro-mechanical coupling at nanoscale. His current interests are on the kinetic description of Morphing Continuum Theory and its applications in turbulence, micro-/nano-scale flow, and high Mach number flow as well as multi-scale modeling of fluid dynamics.
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Relevant Publication:
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James Chen, James D. Lee and Chunlei Liang, Constitutive equations of micropolar electromagnetic fluids, Journal of Non-Newtonian Fluid Mechanics, 166, pp.867-874, 2011
A. Cemal Eringen, Theory of micropolar fluids, Journal of applied mathematics and mechanics, 16, pp.1-8, 1964
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02-24-2016
11:00am - noon (EST)
NIA Room 137
video
Hyperbolic Method for Dispersive PDEs: Same High-Order of Accuracy for Solution, Gradient, and Hessian
In this talk, we introduce a new hyperbolic first-order system for general dispersive partial differential equations (PDEs). We then extend the proposed system to general advection-diffusion-dispersion PDEs. We apply the fourth-order RD scheme of Mazaheri and Nishikawa [Computers and Fluids, 102 (2014), 131-147] to the proposed hyperbolic system, and solve time-dependent dispersive equations, including the classical two-soliton Korteweg-de Vries (KdV) and a dispersive shock problems. We demonstrate that the predicted results, including the gradient and Hessian (second derivative), are in a very good agreement with the exact solutions. We also show that the high-order RD scheme applied to the proposed system accurately captures dispersive shocks without numerical oscillations. We also verify that the solution, gradient and Hessian are predicted with equal order of accuracy.
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Speaker Bio:
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Dr. Alireza Mazaheri is a Computational Aerothermodynamicist at NASA Langley Research center since 2006. Prior to that he worked at Parsons Inc. (as a research engineer), was a postdoctoral fellow at Pittsburgh University (from 2004-2005) and a National Research Council (NRC) postdoctoral fellow at the US Department of Energy (from 2003-2004). He earned PhD from Clarkson University in Mechanical Engineering, MS from Shiraz University in Computational Thermo-Fluid Engineering, and BS from Guilan University in Fluid Mechanics. Alireza has been involved in several NASA programs/projects, including the Space Shuttle, Orion Multi-Purpose Crew Vehicle (MPCV), Dream Chaser, Hypersonic Inflatable Aerodynamic Decelerator (HIAD), High Energy Atmospheric Reentry Test (HEART), etc. His current research interests are on development of high-order methods that are capable in producing accurate and noise-free solution gradients (e.g., velocity gradients, heat flux, shear stresses, etc.) on irregular tetrahedral elements.
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02-10-2016
11:00am - noon (EST)
NIA Room 137
video
Wall-Resolved Large Eddy Simulations of Separated Flows
This talk will discuss our ongoing work on the wall-resolved large eddy simulations (LES) of high Reynolds number separated flows. Such flows are very challenging to predict accurately mainly because of the significant grid resolution requirements for high Reynolds number turbulence. Our goal in these well-resolved simulations is to obtain good-quality reliable data to guide the development of improved/new wall models, which can in turn be used in future wall-modeled simulations of separated flows with significantly reduced computational cost. A turbulence simulation methodology based on high-fidelity numerical schemes is being used to perform the large-scale simulations. This talk will discuss several important issues that were encountered during the course of this work and present representative results from the calculations. Comparisons with available experimental measurements will be made to assess the predictive capability of the simulations.
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Speaker Bio:
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Dr. Ali Uzun joined NIA as a Senior Research Scientist in July 2015. He received his Ph.D. in Aeronautics & Astronautics from Purdue University in 2003. He joined the Florida State University as a post-doctoral research associate immediately after completing his Ph.D. and later became a Research Scientist at the Florida Center for Advanced Aero-Propulsion, Florida State University. His current research interests include computational fluid dynamics using high-order numerical methods, turbulence simulations, computational aeroacoustics and parallel computing.
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01-26-2016
11:00am - noon (EST)
NIA Room 137
video
High-Order Residual-Distribution Schemes for Discontinuous Problems on Irregular Triangular Grids
In this talk, we construct second- and third-order non-oscillatory shock-capturing hyperbolic residual-distribution schemes for irregular triangular grids, extending our previously proposed high-order schemes [J. Comput. Phys., 300 (2015), 455-491, pdf, journal] to
discontinuous problems. We present extended first-order N- and Rusanov-scheme formulations for a hyperbolic advection-diffusion system. We then construct second- and third-order non-oscillatory hyperbolic residual-distribution schemes by blending the non-monotone second- and third-order schemes with the extended first-order schemes as typically done in the residual-distribution schemes, and examine them for discontinuous problems on irregular triangular grids. We also propose to use the Rusanov scheme to avoid non-physical shocks in combination with an improved characteristics-based nonlinear wave sensor for detecting shocks, compression, and expansion regions. We then verify the design order of accuracy of these blended schemes on irregular triangular grids.
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Speaker Bio:
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Dr. Alireza Mazaheri is a Computational Aerothermodynamicist at NASA Langley Research center since 2006. Prior to that he worked at Parsons Inc. (as a research engineer), was a postdoctoral fellow at Pittsburgh University (from 2004-2005) and a National Research Council (NRC) postdoctoral fellow at the US Department of Energy (from 2003-2004). He earned PhD from Clarkson University in Mechanical Engineering, MS from Shiraz University in Computational Thermo-Fluid Engineering, and BS from Guilan University in Fluid Mechanics. Alireza has been involved in several NASA programs/projects, including the Space Shuttle, Orion Multi-Purpose Crew Vehicle (MPCV), Dream Chaser, Hypersonic Inflatable Aerodynamic Decelerator (HIAD), High Energy Atmospheric Reentry Test (HEART), etc. His current research interests are on development of high-order methods that are capable in producing accurate and noise-free solution gradients (e.g., velocity gradients, heat flux, shear stresses, etc.) on irregular tetrahedral elements.
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Relevant Publication:
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Alireza Mazaheri and H. Nishikawa, "High-Order Residual-Distribution Schemes for Discontinuous Problems on Irregular Triangular Grids", AIAA Paper 2016-1331, 54th AIAA Aerospace Sciences Meeting, 4-8 January, San Diego, California, 2016.
[ bib |
pdf
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Alireza Mazaheri and H. Nishikawa, "Improved second-order hyperbolic residual-distribution scheme and its extension to third-order on arbitrary triangular grids", Journal of Computational Physics, 300, pp.455-491, 2015.
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pdf |
journal |
seminar
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11-19-2015
11:00am - noon (EST)
NIA Room 141
video
Integrating Three-Dimensional Stress Evaluation With Rotorcraft Comprehensive Analysis
Rotorcraft comprehensive dynamic simulation is a basic tool in rotorcraft design, optimization, and performance evaluation. Comprehensive rotorcraft analysis implies that the simulation tool integrates the many relevant disciplines, such as aerodynamics, structural dynamics, and controls, but also involves sophisticated models of complex components such as engines or active and passive damping devices, to name just few. Because of computational cost constraints, rotor blade dynamic analysis is based on beam models, which can deal with the complex behavior of anisotropic composite materials. Over the past decade, CFD/CSD coupled simulations have ushered in a new era in comprehensive simulations by providing a quantum jump in the accuracy of aerodynamic loads predictions, although at a greatly increased computational cost. The coupled simulations predict time histories of stress resultants that are in good agreement with flight test measurements. But a truly comprehensive simulation requires the evaluation of three-dimensional stress distributions: blade detailed design, structural integrity, fatigue life, and their optimization all depend on the accurate knowledge of three-dimensional stress distributions. Three-dimensional finite element models could provide the desired level of accuracy but the associated computational cost is overwhelming. In industry, three-dimensional finite element models are used routinely to post-process the predictions of comprehensive analysis tools, but the assumptions inherent to this post-processing step might negate the improved accuracy gained by three-dimensional analysis.
This seminar will describe a general procedure for the dimensional reduction of complex structures made of advanced composite materials. The approach can be viewed as a Global/Local technique, and takes into account distributed (aerodynamic) loading and inertial (vibratory and centrifugal) effects. The three-dimensional state of stress can be recovered at any point in the rotor blade. Comparison with three-dimensional finite element results shows that very high accuracy is achieved, while keeping computational costs three to four orders of magnitude lower than those required by three-dimensional finite element analysis. Complex geometric configurations and material systems can be handled easily.
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Speaker Bio:
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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, senior member of the American Institute of Aeronautics and Astronautics, and member of the American Helicopter Society. 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.
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11-03-2015
11:00am - noon (EST)
NIA Room 137
video
High-Speed Boundary-Layer Transition Induced by a Discrete Roughness Element
Surface protuberances can cause laminar to turbulent transition in high-speed vehicles leading to a higher heating load and skin-friction drag. Hence, understanding the mechanism of transition is important for the design of such vehicles. Direct numerical simulation (DNS) is used to study laminar to turbulent transition induced by a discrete hemispherical roughness element in a high-speed laminar boundary layer using an unstructured finite volume methodology. The simulations are performed under conditions matching the experiments of Danehy et al. (AIAA Paper 2009-394, 2009) performed at the NASA Langley Mach 10 Air Tunnel, for free-stream Mach numbers of 3.37, 5.26 and 8.23. Qualitative comparison to experiment shows good agreement. It is observed that the Mach 8.23 flow remains laminar downstream of the roughness, while the lower Mach number flows undergo transition. A phenomenological mechanism is proposed for the observed behavior. For Mach 3.37 and 5.26, mean statistics downstream of the roughness is compared with available turbulent boundary layer data and show good agreement. The effect of boundary layer thickness on Mach 3.37 flow past a hemispherical bump is also studied keeping all other parameters constant. While the essential mechanism of transition is similar for the conditions studied, differences are observed in the number of trains of hairpin vortices downstream of the roughness element. A Reynolds number based on the skin friction velocity and wall properties is seen to correlate with the onset of transition for the cases considered.
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Speaker Bio:
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Dr. Prahladh S. Iyer is currently working at NIA as a Research Scholar. He obtained his PhD from the Dept. of Aerospace Engg. & Mechanics, University of Minnesota in February 2015 and B.Tech in Chemical Engineering from the National Institute of Technology, Surathkal, India in 2008. His research interests include DNS/ LES of complex flows, transition to turbulence and turbulence modeling.
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Relevant Publications:
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High-speed boundary-layer transition induced by a discrete roughness element, Prahladh S. Iyer and Krishnan Mahesh,
J. Fluid Mech., Volume 729, August, 2013, pp. 524-562.
[ journal ]
Discrete roughness effects on high-speed boundary layers, Prahladh S. Iyer,
Doctoral Dissertation, University of Minnesota, 2015.
[ Ph.D. Thesis ]
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10-27-2015
11:00am - noon (EST)
NIA Room 141
video
Observation of Novel Dynamics for a Low-Boom Relaxed-Compression Supersonic Inlet
The future of commercial supersonic flight requires low-boom aircraft design. To accomplish this, a relaxed-compression inlet design has been proposed and shown to dramatically reduce the shock signatures of the propulsion system. However, little is known about the unsteady fluid dynamics of such inlets, especially at or near on-design conditions. In the present study, it is shown that these dynamics are inconsistent with the dynamics of conventional supersonic inlets. The present study employed spectral analysis of a low-boom axisymmetric external compression inlet using Schlieren video and experimental unsteady surface pressure transducer readings as a function of mass flow rates. The experimental data was at Mach 1.67 in the 8'x6' supersonic wind tunnel at the NASA Glenn Research Center. A 5 kHz sampling rate is used for surface pressure transducer readings while the shock motion was captured with Schlieren video frames at 2,000 frames per second, and processed using image-threshold analysis to determine fluctuations in external shock position. Power spectral density plots are used to reveal the dominant excitation modes for both the normal shock and surface pressure fluctuations. These fluctuations are minimal at the design mass flow rate case of 98.5% mass flow ratio (MFR) but became significant for a near-design MFR of about 95.5%. These pressure fluctuations were a strong function of pressure tap location and did not correspond to the conventional Ferri criterion of conventional supersonic inlets.
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Speaker Bio:
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Dr. Eric Loth, the Chair of Mechanical and Aerospace Engineering (MAE) at the University of Virginia, is a PhD graduate of the University of Michigan. In 1990, he started as a faculty member at the University of Illinois, where he rose to the position of Professor, Willett Faculty Scholar, and Associate Head of Aerospace Engineering. In 2010, he joined the University of Virginia and later became its first Rolls-Royce Commonwealth Professor. Among many awards and distinctions, Dr. Eric Loth has been named a Fellow of the American Society of Mechanical Engineers, a Fellow of the National Center for Supercomputing Applications, and a Fellow at Magdalene College at Cambridge University. Research by Dr. Eric Loth and his students has resulted in more than 300 publications on a wide variety of topics including wind energy, unsteady aerodynamics, supersonic propulsion, multiphase flow, and micro-/nano-scale fluid dynamics.
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10-20-2015
11:00am - noon (EST)
NIA Room 137
video
Advances in Global Instability Computations: from Incompressible to Hypersonic flows
Hydrodynamic instability theory studies the behavior of unperturbed flow fields upon the introduction of small-amplitude perturbations in order to improve the understanding of the processes involved in the onset of unsteadiness and the transition of laminar flow to a turbulent regime. The present work constitutes a step forward in advancing the frontiers of knowledge of fluid flow instability from a physical point of view, as a consequence of having been successful in developing groundbreaking methodologies for the efficient and accurate simulation of the transition phenomena in complex realistic three-dimensional flows. These achievements have been possible due to the huge computational efficiency improvements of the newly developed instability code for solving the very large sparse matrices discretizing the 2D and 3D partial differential equations (PDEs) governing the linear global instability analysis theories. The code implements high-order stable finite difference schemes for spatial discretization, which allows the use of efficient sparse linear algebra techniques without sacrificing accuracy. This permits a drastic reduction of the computing hardware on which state-of-the-art global instability analysis are performed. Furthermore, the extensibility of the novel three-dimensional parabolized stability equations (PSE-3D) algorithm developed in the framework of the present work to also study nonlinear flow instability permits transition prediction in complex flows of industrial interest, thus extending the classic PSE concept which has been successfully employed in the same context to boundary-layer type of flows over the last three decades.
Typical examples of incompressible flows, the instability of which has been analyzed without the need to resort to the restrictive assumptions used in the past, range from isolated vortices, and systems thereof, in which axial homogeneity is relaxed to consider viscous diffusion, as well as turbulent swirling jets, the instability of which is exploited in order to improve flame-holding properties of combustors. The instability of the wake of an isolated roughness element in a supersonic and hypersonic boundary-layer has also been analyzed with respect to its instability: excellent agreement with direct numerical simulation results has been obtained in all cases. Finally, instability analysis of Mach number 7 flow around an elliptic cone modeling the HIFiRE-5 flight test vehicle has unraveled flow instabilities over the entire geometry, results comparing favorably with ground and flight test predictions.
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Speaker Bio:
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Dr. Pedro Paredes is currently a Post-doctoral Fellow at NASA Langley Research Center. He received his Ph.D. in Aerospace Engineering from Technical University of Madrid in Mach 2014. His research interests include linear flow instability and control of complex flows and study of laminar-turbulent transition in compressible boundary layers.
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Relevant Publication:
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Advances in Global Instability Computations: From Incompressible to Hypersonic Flow, Pedro Paredes
[ Ph.D. Thesis (pdf) ]
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09-29-2015
11:00am - noon (EST)
NIA Room 137
video
Third-Order Edge-Based Scheme and New Hyperbolic Navier-Stokes System
This talk will discuss a special third-order edge-based scheme and new hyperbolic Navier-Stokes formulations, HNS17 and HNS20. The edge-based scheme achieves third-order accuracy on simplex elements by linear flux extrapolation and with straight-edge grids. The scheme is highly efficient in that the residual is computed over a loop over edges with a single flux evaluation per edge. This efficient scheme, originally discovered for hyperbolic conservation laws by Katz and Sankaran, is made immediately applicable to viscous terms by a hyperbolic viscous formulation. A versatile hyperbolic formulation, HNS20, is introduced to enable accurate computations of the gradients of all primitive variables. It allows us to construct not only superior Navier-Stokes discretizations but also a third-order inviscid and second-order viscous discretization by second-order algorithms. New techniques, artificial hyperbolic diffusion and dissipation, which are essential to the new formulations, are also introduced to raise the order of accuracy of the velocity and density gradients by one order.
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Speaker Bio:
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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, etc., and joined NIA in 2007.
His area of expertise is the algorithm development for CFD, focusing on
hyperbolic methods for robust, efficient, highly accurate viscous discretization schemes.
[ Homepage |
Hyperbolic Method |
CFD book |
Free CFD codes |
CFD Notes
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Relevant Publications:
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Alternative Formulations for First-, Second-, and Third-Order Hyperbolic Navier-Stokes Schemes, AIAA Paper, 2015-2451.
[ AIAA Paper 2015-2451 (pdf) ]
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09-15-2015
11:00am - noon (EST)
NIA Room 137
video
High-Fidelity Simulations of Complex High-Speed Flows
This talk will present sample applications of high-fidelity numerical simulations to complex problems that contain high-speed flow phenomena. Example applications include prediction of noise generated by high-speed free/impinging jets and detailed simulation of resonance-enhanced micro-actuators that generate pulsed high-momentum supersonic micro-jets for flow/noise control applications. A large eddy simulation (LES) methodology based on high-fidelity numerical schemes developed for turbulence simulations and computational aeroacoustics (CAA) has been utilized to perform the large-scale simulations. This talk will provide an overview of the numerical methods implemented in the simulation methodology and present representative results from the calculations. Comparisons with available experimental measurements will be made to assess the predictive capability of the simulations.
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Speaker Bio:
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Dr. Ali Uzun recently joined NIA as a Senior Research Scientist. He received his Ph.D. in Aeronautics & Astronautics from Purdue University in 2003. He joined the Florida State University as a post-doctoral research associate immediately after completing his Ph.D. and later became a Research Scientist at the Florida Center for Advanced Aero-Propulsion, Florida State University. His current research interests include computational fluid dynamics using high-order numerical methods, turbulence simulations, computational aeroacoustics and parallel computing.
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09-08-2015
11:00am - noon (EST)
NIA Room 137
video
Is Curved-Element a Necessity for all High-Order Schemes?
In this talk, which covers part of a recent JCP paper we published
http://dx.doi.org/10.1016/j.jcp.2015.07.054 , we present a new efficient third-order scheme that is capable in producing accurate and smooth solution gradients on irregular triangular elements. We discuss, in depth, how this scheme is constructed and why this scheme produces truly third-order solution and solution gradients on linear (straight-sided) elements even for geometries containing curved boundaries that are represented with straight edges. At the end we also show a (universal) technique in evaluating high-order integrated quantities (using high-order data) on curved boundaries.
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Speaker Bio:
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Dr. Alireza Mazaheri is a Computational Aerothermodynamicist at NASA Langley Research center. He earned his BS from Guilan University in Fluid Mechanics, MS from Shiraz University in Thermo-Fluid Engineering, and PhD from Clarkson University in Mechanical Engineering. He then worked as a National Research Academies (NRC) postdoctoral research fellow at the US Dept. of Energy before working in academies and industries (e.g., McGowan Inst. for Regenerative Medicine, Pittsburgh University, and Parsons Inc.). Alireza then joined NASA in 2006 and has been involved in several NASA programs/projects since then, including the Space Shuttle, Orion Multi-Purpose Crew Vehicle (MPCV), Dream Chaser, Hypersonic Inflatable Aerodynamic Decelerator (HIAD), High Energy Atmospheric Reentry Test (HEART), etc. He is currently focusing on advancing the state of the art CFD technology by developing schemes that are capable in producing accurate solution gradients (e.g., heat flux, shear stresses, etc.) on purely tetrahedral elements.
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Relevant Publication:
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A. Mazaheri and H Nishikawa, Improved Second-Order Hyperbolic Residual-Distribution Scheme and its Extension to Third-Order on Arbitrary Triangular Grids, J. Comput. Phys. (2015) [
journal paper ]
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08-25-2015
11:00am - noon (EST)
NIA Room 137
video
Third-Order Active Flux Schemes for Advection Diffusion
We extend the third-order active-flux diffusion scheme introduced in Ref.[AIAA Paper 2014-2092] to advection diffusion problems. It is shown that a third-order active-flux advection-diffusion scheme can be constructed by adding the advective term as a source term to the diffusion scheme. The solution gradient, which is computed simultaneously to third-order accuracy by the diffusion scheme, is used to express the advective term as a scalar source term. To solve the residual equations efficiently, Newton's method is employed rather than explicit pseudo-time iterations, which requires a large number of residual evaluations. For unsteady computations, it leads to a third-order implicit time-stepping scheme with Newton's method. Numerical experiments show that the resulting advection-diffusion scheme achieves third-order accurate and the Newton solver converges very rapidly for both steady and unsteady problems.
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Speaker Bio:
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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, etc., and joined NIA in 2007.
His area of expertise is the algorithm development for CFD, focusing on
hyperbolic methods for robust, efficient, highly accurate viscous discretization schemes.
[ Homepage |
CFD book |
Free CFD codes |
CFD Notes
]
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Relevant Publication:
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H. Nishikawa, "Active Flux for Advection Diffusion", AIAA Paper 2015-2450, 22nd AIAA Computational Fluid Dynamics Conference, Dallas, 2015.
[ pdf ]
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