CTR events

Laser-induced breakdown is a versatile means of depositing energy in a fluid and a promising alternative to conventional electrode-spark ignition for combustion systems.  Using numerical simulations we analyze the flow dynamics following the laser pulse and show that it is sensitive to even subtle alterations in the plasma kernel, which lead to qualitative changes in the flow pattern and ejections of hot gas from the laser focal region.  This sensitivity is leveraged in a dual-pulse configuration, in which the timing and positioning of the pulses can be controlled to enhance dispersal of ho... Read More

Direct combustion noise plays a key role in the triggering and dynamics of thermo-acoustic instabilities of modern gas turbines. Moreover, many combustion devices can produce high levels of noise, while being subjected to stringent noise regulations. Achieving a better understanding of the sound production by premixed flames is important for designing safer and quieter combustion devices. The presented research has for goals to study the mechanisms involved in the sound generation process of turbulent premixed jet flames using DNS. State of the art post-processing methods are used to analyz... Read More

Rocket engines and high-power new generations of jet engines and diesel engines oftentimes involve the injection of one or more reactants at subcritical temperatures into combustor environments at high pressures, and more particularly at pressures higher than those corresponding to the critical points of the separate components, which typically range from 13 to 50 bars for most propellants. This class of trajectories in the thermodynamic space has been traditionally referred to as transcritical. However, the fundamental understanding of fuel atomization, vaporization, mixing, and combustion... Read More

The use of computational fluid dynamics for external aerodynamic applications has been a key tool for aircraft design in the modern aerospace industry. In the last decades, large-eddy simulation with near-wall modeling (wall-modeled LES) has gained momentum as a cost-effective approach for both scientific research and industrial applications. In this talk, we discuss current challenges of wall-modeled LES to become a design tool for the aerospace industry.  We focus first on the working principles and performance of wall-modeled LES for external aerodynamic applications, with emphasis on re... Read More

Shock-induced scalar mixing and ignition under canonical shock-turbulence interactions (STI) will be considered first, by means of Direct Numerical Simulation in 3D and 2D, respectively. The effects of relevant physical parameters (shock and turbulence Mach numbers, and Reynolds number) will be highlighted on statistical changes along the shock-normal direction of scalar variance and dissipation-rate budgets, flow topology, and alignments of the scalar gradient with vorticity and strain-rate eigendirections. Shock-induced scalar mixing will also be addressed by tracking the downstream evolu... Read More

An overview of several available methods for prediction of the transition location is presented. Two particular methods are discussed – the eN method, and the empirical, correlation-based, model of Langtry & Menter (2009). The role of stability theory is explored, including local stability theory, incorporation of non-parallel effects (parabolized stability equations), and extensions into the nonlinear regime. Limitations and drawbacks are pointed out and possible future paths for improvement are highlighted. An area of particular interest is the receptivity stage, where environmental d... Read More

Biologically generated turbulence has been proposed as an important contributor to nutrient transport and ocean mixing. However, for swimming animals to produce non-negligible transport and mixing, they must produce eddies at scales comparable to the length scales of stratification in the ocean. It has previously been argued that biologically generated turbulence is limited to the scale of the individual animals involved, which would make turbulence created by highly abundant centimeter-scale zooplankton such as krill irrelevant to ocean mixing. Their small size notwithstanding, zooplankton... Read More

Unconditionally stable implicit time-marching methods are powerful in efficiently solving stiff differential equations. In this talk, I will present a novel unified framework for handling both physical and numerical stiffness based on Time-Accurate and highly-Stable Explicit (TASE) operators.

The proposed TASE operators act as preconditioners on the stiff terms and can be readily deployed to most existing explicit time-marching methods. The resulting time integration method remains the original explicit time-marching schemes, yet with nearly unconditional stability. The TASE operator... Read More

Interfacial mixing and transport are nonequilibrium processes coupling kinetic to macroscopic scales. They occur in plasmas, fluids, and materials over celestial events to atoms. Grasping their fundamentals can advance a broad range of disciplines in science, mathematics, and engineering. This work focuses on the long-standing classic problem of stability of a phase boundary - a fluid interface that has a mass flow across it. We briefly review the recent advances and challenges in theoretical and experimental studies, develop the general theoretical framework directly linking the microscopi... Read More

Turbulent combustion is an extremely challenging “multi-multi” problem: multi-physics, multi-scale, and multi-species. Since not all scales of turbulence and combustion can be resolved in DNS for practical conditions of interest, models are required for the unresolved turbulent combustion processes in LES and RANS. However, the large number of thermochemical scalars required to describe combustion chemistry (potentially hundreds or thousands of chemical species) means that the unresolved state-space that needs to be modeled is extremely high-dimensional. Turbulent combustion models can gene... Read More