CTR events

Combustion devices are prone to combustion instabilities (CIs). They classically occur when heat release rate oscillations and acoustic fluctuations become coherent, creating constructive interferences. To predict the occurrence of CIs in combustion devices, one must account for 1) the acoustic waves in the entire combustion system and 2) the flame response to these fluctuations. The former can only be obtained if the acoustic properties of the boundaries are properly prescribed. During this seminar, a Time Domain Impedance Boundary Condition (TDIBC) method will be presented as well as a mo... Read More

The impingement of electric fields on flames is known to have potential for mitigating combustion instabilities, enhancing flame propagation, and decreasing pollutant emissions. In particular, electric fields can be used to steer ions produced inside the flame in opposite directions depending on their sign. These ions collide and exchange momentum with the surrounding neutral molecules, which leads to modifications in the flow field. In this talk, steady axisymmetric numerical simulations of methane/air counterflow laminar diffusion flames are employed in order to analyze the effects of the... Read More

Turbulent flows in the presence of bounding surfaces, as those occurring in oceanic and atmospheric currents, around vehicles, or inside pipes, may be apprehended as a collection of whirls or eddies. These eddies follow a regeneration cycle, i.e, existing eddies are seeds for the origin of new ones and so forth.  Understanding this process is critical for the modeling and control of geophysical and industrial flows where a non-negligible fraction of the energy is dissipated by turbulence in the immediate vicinity of walls. In the present work, we examine the causal interactions among energy... Read More

We have developed a new pressure-correction method for simulating incompressible flows over curved walls. The methodology is applicable to DNS, LES and RANS. We chose the orthogonal formulation of the Navier-Stokes equations in curvilinear coordinates vs the generalized curvilinear coordinates because the computational cost of advancing the numerical solution of the governing equations in time is substantially reduced as the orthogonal formulation does not contain cross-derivatives in the advection, diffusion, Laplacian, and gradient operators. As a result, the numerical stencils of the fin... Read More

The COOLFluiD (Computational Object Oriented Libraries for Fluid Dynamics) project, which started in 2002 as a joint effort between the Von Karman Institute for Fluid Dynamics (VKI) and the Center for mathematical Plasma Astrophysics (CmPA) at the University of Leuven (KUL), has led to the development of a world-class open source platform for HPC and multi-physics modelling. Within this framework, research efforts have been devoted particularly to the modeling of space re-entry aerothermodynamics and magnetized plasmas. The former includes the development of models/algorithms for simulating... Read More

In this talk we investigate amplifying behavior of small perturbations about Reynolds-averaged Navier-Stokes solutions of high-speed turbulent jets using input-output (I/O) analysis.  Inspired by control theory in electrical engineering, our method investigates how input forcing (jet turbulence) leads to output noise.  Singular value decomposition of the resolvent of the linearized Navier-Stokes equations forms an orthonormal set of I/O mode pairs, sorted in descending order by the magnitude of the corresponding singular values.  In this way we find that the input modes capture coherent str... Read More

Protecting a spacecraft during atmospheric entry is one of highest risk factors that needs to be mitigated during design of a space exploration mission. At entry speeds from space, air turns into high-temperature plasma, and spacecraft Thermal Protection Systems (TPS) are needed to protect the vehicle payload. Modern successful material architectures of spacecraft shields use a porous carbon fiber substrate impregnated with phenolic as an ablator material. In the lecture, efforts to build a Predictive Material Modeling framework for porous ablators from micro-scale to macro-scale will be pr... Read More

Turbulent flows laden with particles are widely encountered in a great number of natural physical processes and in a host of industrial and environmental applications. In these flows there exist complex interactions between inertial particles, flow turbulence and heat transfer, many of which have not yet been adequately investigated and still remain open questions. In this talk, we will present the results of direct numerical simulations of particle-laden spatially developing turbulent boundary layer flows, using a two-way coupled Eulerian-Lagrangian approach. The main focus of this work is... Read More

This talk describes how to account for second-order statistics of turbulent flows using low-complexity stochastic dynamical models based on the linearized Navier-Stokes (NS) equations. The complexity is quantified by the number of degrees of freedom in the linearized evolution model that are directly influenced by stochastic excitation sources. For the case where only a subset of correlations are known, we develop a framework to complete unavailable second-order statistics in a way that is consistent with linearization around turbulent mean velocity. In general, white-in-time stochastic for... Read More

The interaction of turbulence with shock waves, while very common in nature and engineering systems, is a very difficult problem from a theoretical, numerical and experimental perspective. A main challenge arise from the two-way coupling between the shock and turbulence which occurs at a wide range of scales in time and space. The focus of this work is on the fundamental understanding of these shock-turbulence interactions (STI) at high turbulence intensities with high-fidelity direct numerical simulations (DNS) that fully resolve the shock. The numerical study is guided by novel theoretica... Read More