CTR events

In response to the global SARS-CoV-2 transmission pandemic, the Sandia National Laboratories Rapid Lab-Directed Research and Development (LDRD) COVID-19 initiative, in partnership with a multi-laboratory CARES Act research project, deployed a multi-physics, droplet-laden, turbulent low-Mach simulation tool to model pathogen-containing water droplets that emanate from synthetic human coughing and breathing events. A high-fidelity, low-Mach computational fluid dynamics (CFD) simulation tool that includes evaporating droplets and variable-density, buoyant turbulent flow coupling is well-suited... Read More

Although hydrodynamic turbulence and shock formation have been treated separately in previous literature, both are characterized by an energy cascade from large to small scales due to nonlinear interactions. Therefore, the numerical simulation of both phenomena could be treated in a similar fashion, that is by solving the filtered compressible Navier-Stokes equations.

In this talk, Victor Sousa will discuss a new perspective on closures for filtered governing equations that allows for a unified framework for shock capturing and subfilter turbulence modeling. This concept will be full... Read More

Laser-induced breakdown is a versatile means of depositing energy in a gas and seeding ignition of a combustible mixture, and it offers multiple advantages over conventional approaches.  To analyze the laser-generated flow and ensuing ignition dynamics, direct numerical simulations are conducted in several configurations: a quiescent gas, a temporally evolving shear layer, and a model gas-gas rocket combustor.  Consistent with experimental observation, it is shown that ignition is possible even when energy is deposited in a non-flammable region of the flow, due to a laser-generated vortex o... Read More

A "length scale" in a fluid flow does not exist as an independent entity but is associated with the specific flow variable being analyzed. While this may seem obvious, we often discuss the "inertial range" or the "viscous range" of length scales in turbulence as if they exist independently of a flow variable, which in incompressible turbulence is the velocity field. How should we analyze "length scales" in flows with significant density variations, such as across a shock or in multiphase flows? I will discuss different possible decompositions and how only one of them unravels an inertial ra... Read More

Turbulent wakes are ubiquitous in nature and man-made environments. In oceans and the atmosphere, these wakes are generally affected by the presence of stratification. In this talk, I will discuss how the shape of the wake generator influences the course of evolution of turbulent wakes from the perspective of (a) coherent structures and (b) mean/turbulence scalings. In the first part (a), we extract and analyze coherent structures in stratified disk wakes at a moderately high Reynolds number Re = 50,000 and Froude numbers Fr = 2 and 10. The vortex shedding (VS) mechanism is dominant at inte... Read More

Recent experimental and computational studies have demonstrated that wall-bounded turbulent shear flows exhibit universal  small-scale  dynamics  that  are  modulated  by  large-scale  flow  structures.  This  characterization  can  be complicated, however, by stronger pressure gradients; they can cause significant variation of the mean flow in the streamwise direction. For such situations, we perform asymptotic analysis of the Navier-Stokes equations valid whenever  the  viscous  length  scale  is  small  relative  to  the  length  scale  over  which  the  mean  flow  varies.  The asymptot... Read More

Combustion instabilities (CIs) are one of the major challenges for the design and operation of gas turbines and rocket engines. While most studies examined CIs for premixed systems due to their propensity to be more unstable, instabilities have also been observed in partially premixed and non-premixed flames for a variety of configurations. This talk will tackle three aspects crucial to the understanding of transverse CIs in non-premixed systems: the response of the injector flow to acoustic excitation, the coupling mechanisms occurring in acoustically forced flames, and the modeling of the... Read More

This presentation will detail some of my recent works related to the formulation and computation of data-driven reduced-order models for fluid flows.

In the first part, the concept of Flame Transfer Function (FTF) is introduced. This low-order model, based on a simple Fourier transform, is one of the most common in thermoacoustics, where it is used to represent the dynamical response of a flame to acoustic perturbations. The challenge of the present work lies in the configuration for which a FTF is computed: it consists of a doubly-transcritical LO2-LCH4 coaxial jet-flame, typical of... Read More

Rotors form an integral part of many flow machines, e.g. propellers, helicopters, wind turbines, turbo-machinery, etc. Although many computational models (differing in complexity and starting assumptions) for the estimation of their aerodynamic properties exist, accurately simulating flows around rotors still presents a challenge (due to unsteadiness, turbulence, flow separation, and other flow phenomena). This presentation will focus on some of the commonly most employed computational approaches and present some of the most characteristic quantitative and qualitative results obtained for a... Read More

Developing accurate, stable, and thermodynamically consistent numerical methods to simulate two-phase flows is critical for many applications. We develop numerical methods to solve thermodynamically consistent Cahn-Hilliard Navier-Stokes equations to simulate two-phase flows with deforming interfaces at various density contrasts. We develop three essentially unconditionally energy-stable time integration schemes. The first two time-integration schemes are fully implicit based on the pressure-stabilization technique. The third approach utilizes the projection method to decouple the pressure... Read More