CTR events

This talk summarizes part of the work performed during our 3-year Laboratory Directed Research and Development - Directed Research (LDRD-DR) project, titled MachinE Learning for Turbulence (MELT).  Started in October 2018, the project partially covered ~10 staff members, 7 postdocs, several more summer students, and addressed a diverse set of topics related to turbulence and applications in climate and astrophysics.  Today, in order to highlight the exploratory aspect of such projects, I will survey some of our results on a) neural network (NN) models of scalar turbulence, b) learning Lagra... Read More

While significant progress has been made in the past decade to predict atomization using detailed numerical simulations, these simulations come at significant computational cost since the range of scales that must be resolved typically exceeds those of a single phase turbulent flow significantly. A switch to a Large Eddy Simulation (LES) approach would be desirable, however, the underlying assumption of LES methods that the dynamics of the unresolved sub-filter scale can be inferred from the dynamics of the resolved scales is questionable when atomization occurs. Similar to viscosity in sin... Read More

The ambitious performance goals set by the aerodynamic as well as the turbomachinery industries call for more accurate, scale-resolving simulation tools. A viable path towards industrial-level scale-resolving simulations of flows at high Reynolds numbers is through wall-modeled large-eddy simulation (WMLES). This talk will discuss the best practice in WMLES of problems in which heat transfer plays a role, covering topics including the gird resolution, the LES/wall-model matching location, the low Mach number limit, and the turbulent Prandtl number. Special attention is given to problems at... Read More

Turbulent breaking waves entrain air cavities that break up and coalesce to form polydisperse clouds of bubbles. We recently provided theoretical and numerical justification that the dominant mechanism for super-Hinze-scale bubble generation is a fragmentation cascade from large to small sizes sustained by turbulent velocity fluctuations. This behavior should be universal across various turbulent bubbly flows because of the size locality inherent in a cascade. Universality simplifies the development of subgrid-scale (SGS) breakup models in two-phase large eddy simulations (LES). We formulat... Read More

When I first arrived at CTR as a postdoctoral fellow in 1992, I could feel deep rumblings beneath my feet. I knew that California was famous for its seismic activity but this was of a different kind. It originated from something called the “Dynamic Model”: the greatest idea in turbulence modeling in a long time that “worked” but did not make sense. I would like to talk
about our efforts to make sense of it all and the intellectual atmosphere at CTR in the 1990’s.

Link to video file:
... Read More

At 30 years old, the Germano identity-based dynamic model for turbulence simulations can be said to have become a classic result for the field of turbulence. In this presentation, I will recall how several of its variants (e.g. Lagrangian, scale-dependent, multiplicative) came about and summarize the main ideas underlying these variations on an elegant theme.

Link to video file:
The dynamic model for LES and variations on the theme

In the immediate aftermath of the 1990 Summer Program, there was a flurry of activities at CTR seeking to exploit the dynamic modeling concept in canonical turbulent flows which heretofore had challenged the universality of turbulence models. I will discuss extensions to compressible flow, scalar transport, reacting flows and other potential formulations
of the dynamic modeling concept that were considered.

Link to video file:
At last, Turbulence closure modeling minus tu... Read More

It was a sunny morning in July 1990, the first week of the CTR Summer Program, Massimo Germano, Parviz Moin, Bill Cabot and Ugo Piomelli met to discuss the possible uses of an identity that Massimo Germano had recently derived. This talk will chronicle how the events of that month produced one of the most influential subgrid-scale models for large-eddy simulations.

Link to video file:
https://stanford.box.com/s/8x6oamqqc9v68ot9d860wq411sgiyzk4

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