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CTR events

Quantification of Modeling Uncertainties in Turbulent Flow Simulations

: Tea Seminar
Friday, November 13, 2015 - 4:00pm
Speaker(s):
Wouter Edeling, CTR Postdoctoral Fellow
Abtract:

Our goal is to make predictive simulations with Reynolds-Averaged Navier-Stokes (RANS) turbulence models, i.e. simulations with a systematic treatment of model and data uncertainties and their propagation through a computational model to produce predictions of quantities of interest with quantified uncertainty [1]. To do so, we make use of the robust Bayesian statistical framework, in which the uncertainty is represented by probability.

We search for estimates of the uncertainties in the space of model coefficients, for a large range of different calibration scenarios. To capture the... Read More

Bio:
Wouter Edeling received his PhD from Arts et Metiers ParisTech and Delft University of Technology. The subject was the quantification of modeling uncertainties in turbulent flow simulations. His MSc... Read More

Interaction between the atmospheric boundary layer and wind turbines

: Tea Seminar
Friday, November 6, 2015 - 4:00pm
Speaker(s):
Mahdi Abkar, CTR Postdoctoral Fellow
Abtract:

Wind turbines extract kinetic energy from the ambient flow in the turbulent atmospheric boundary layer (ABL). A profound understanding of the mutual interactions between ABL and wind turbines will indeed shed light on the path to the optimized wind farms. Apart from parameters like wind turbine sittings relative to the incoming wind, the wind farm performance is entangled with ABL flow whose structures and dynamics change by the variation of land-surface fluxes, geostrophic forcing and topography. Wind farms have also been reported to change land-surface fluxes (e.g. momentum, heat, moistur... Read More

Bio:
Mahdi Abkar received his Ph.D. in Mechanical Engineering from École Polytechnique Fédérale de Lausanne (EPFL), Switzerland, in 2014. His research interests lie on Computational fluid dynamics,... Read More

Lagrangian subgrid modelling for the relative separation of tracers in turbulence

: Tea Seminar
Friday, October 2, 2015 - 4:00pm
Speaker(s):
Dr. Federico Toschi, Team Leader PIV, German Aerospace Center
Abtract:

Turbulence has an important influence on the transport of small particulate matter like dust in the atmosphere, fuel droplets in combustion chambers and small biological organisms in marine environments.

The relative separation of small tracer particles is strongly influenced by the multi-­‐scale space and time correlations of the turbulent velocity field. While in applications it is often necessary to model the smallest turbulent scales, this may have an important impact on particles’ dynamics and in particular on their relative dispersion.

We present recent results on the d... Read More

Bio:
Professor Federico Toschi holds the chair of Computational Physics of Multi-­‐scale Transport Phenomena in the department of Physics and in the Department of Mathematics and Computer Science at... Read More

Shake-­The-­Box: A 4D-­PTV method for turbulence characterization at high particle densities

: Tea Seminar
Friday, September 18, 2015 - 4:00pm
Speaker(s):
Dr. Andreas Schröder, Team Leader PIV, German Aerospace Center
Abtract:

In order to increase the prediction capabilities of advanced numerical methods for turbulent (wall bounded) flows at relatively high Reynolds numbers, accurate experimental validation data-­sets including the full Reynolds stress tensor at high spatial resolution are urgently required. In particular the influence of pressure gradients and wall curvatures up to flow separation and the development of related shear layers need to be investigated experimentally in order to provide reliable data for the validation process and also to validate scaling laws, sub-­grid and turbulence-­models. Furth... Read More

Bio:
Andreas Schroeder from DLR Goettingen, Team Leader PIV, German Aerospace Center, Gottingen, Germany. He is working on the development of PIV, PTV and some other image based measurement techniques for... Read More

Turbulent Flow over Bluff Bodies: From Sub-Critical to Super-Critical Flow Regimes

: Tea Seminar
Friday, September 11, 2015 - 4:00pm
Speaker(s):
Oriol Lehmkuhl, Professor, Technical University of Catalonia, Spain
Abtract:

This seminar will focus on the numerical simulation of the turbulent flow past bluff bodies which is of importance due to its presence in many engineering applications (flows past an airplane, submarine, automobile, in turbomachines, etc.). The numerical simulation of turbulent flows is a powerful tool for investigating and understanding the turbulence phenomena, and sheds light on the physics of turbulent flows with massive separation. The advances in computational fluid dynamics (CFD) together with the increasing capacity of parallel computers have made possible to tackle such complex pro... Read More

The outer zone of turbulent boundary layers

: Tea Seminar
Monday, August 17, 2015 - 4:00pm
Speaker(s):
Prof. Javier Jimenez, Professor of Fluid Mechanics, School of Aeronautics, Universidad Politecnica de Madrid, Spain
Abtract:

Using data from new simulations of the turbulent boundary layer, we describe several features of the outer zone of wall-­bounded flow at relatively high Reynolds numbers (Reth=6600). For example, using two-point velocity correlations, we show that the size and inclination of the different velocity components are different, and interpret this as representing different moments in their evolution. Other features are not so well understood, E.g., the transverse components (v and w) are similar in boundary layers and channels, but the streamwise velocity is much longer in the latter, and the out... Read More

Modeling The Pressure Strain Correlation Under Uncertainties

: Tea Seminar
Friday, August 7, 2015 - 4:00pm
Speaker(s):
Dr. Aashwin Mishra, Dept. of Aerospace Engineering, Texas A&M University
Abtract:

The cardinal issues forestalling a better understanding of the turbulence phenomenon are the nonlinearity of the inertial cascade physics and the non-local nature of the action of pressure. In this talk, we focus on analyzing, understanding and modeling the latter, manifested in the pressure strain correlation.

The Reynolds stresses provide an insufficient basis to describe the internal structure of turbulent flows, leading to an inherent degree of uncertainty in predictions using classical turbulence models. We carry out a detailed Dynamical Systems analysis of modal ensembles and i... Read More

Bio:
Aashwin Mishra received his Ph.D. in Aerospace Engineering from the Texas A&M University in 2014. His research interests include Turbulence Theory & Modeling, Dynamical Systems & Chaos,... Read More

Numerical Modeling Of Separated Flows At Moderate Reynolds Numbers Appropriate For Turbine Blades And Unmanned Aero Vehicles

: Tea Seminar
Friday, July 31, 2015 - 4:00pm
Speaker(s):
Dr. Giacomo Castiglioni, Aerospace Engineering, University of Southern California
Abtract:

Flows over airfoils and blades in rotating machinery, for unmanned and micro-aerial vehicles, wind turbines, and propellers consist of a laminar boundary layer near the leading edge that is often followed by a laminar separation bubble and transition to turbulence further downstream. Typical Reynolds averaged Navier-Stokes turbulence models are inadequate for such flows. Direct numerical simulation is the most reliable, but is also the most computationally expensive alternative. This work assesses the capability of immersed boundary methods and large eddy simulations to reduce the computati... Read More

Bio:
Dr. Giacomo Castiglioni graduated with a Bachelor of Science in Mechanical Engineering from the Polytechnic University of Milan (Italy) in 2009, and received his Master of Science in Aerospace... Read More

Numerical study of ignition and light-around process in aeronautical gas turbines.

: Tea Seminar
Friday, July 24, 2015 - 4:00pm
Speaker(s):
Dr. Lucas Esclapez, CTR Postdoctoral Fellow
Abtract:

For safety reasons, in-flight relight of the engine must be guaranteed over a wide range of operating conditions but the increasing stringency of pollutant emission constraints requires the development of new aero-engine combustor whose design might be detrimental to the ignition capability. To improve the knowledge of the ignition process in aeronautical gas turbines and better combine conflicting technological solutions, current research relies on both complex experimental investigations and high fidelity numerical simulations. Numerical study of the ignition process in gas turbines from... Read More

Bio:
Dr. Lucas Esclapez just received his PhD. conducted at CERFACS from Institut National Polytechnique of Toulouse (France). His research focuses Large-Eddy Simulation (LES) of the ignition process in... Read More

DNS AND LES OF STABILIZATION AND INSTABILITIES IN ROCKET ENGINES

: Tea Seminar
Friday, July 10, 2015 - 4:00pm
Speaker(s):
Dr. Thierry Poinsot, Research Director, CNRS, Toulouse and Head of CFD group CERFACS
Abtract:

Liquid fuel rocket engines using H2/O2 combustion are again a major research theme in Europe especially for the future Ariane 6 rocket. This talk will present recent progress in two critical mechanisms controlling combustion in cryogenic H2/O2 rocket engines. (1) the stabilization zone of the H2/O2 flame on the lips of a coaxial injector will be studied using DNS with full chemistry and a dual resolution of heat transfer within the splitter plate of the injector. (2) the first full LES of a complete rocket engine installed at DLR Lampoldshausen will be described. Using LES and a simplified... Read More

Bio:
Dr Thierry Poinsot is a research director at CNRS Toulouse (IMFT lab), head of the CFD group at CERFACS and senior research fellow at Stanford University. He has authored more than 180 papers in... Read More

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