CTR events

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

A new formulation for near-wall filtering the Navier-Stokes equations without commutation errors will be detailed in the presentation. In addition, a new split of the dependent variables into large scales and sub-filter scales is formulated where the filtered large scales are not affected by further filtering (i.e. the filtered “filtered scales” are the “filtered scales”), thus removing the Leonard terms from the filtered equations. Finally, closure models for the near-wall effects on the large scales are proposed.

Many innovative catalytic technologies have been developed in the past decade as a response to the world’s rapidly growing demand for a more efficient and sustainable exploitation of energy and material resources. An example is oxidative coupling of methane (OCM), which is considered one of the most promising processes to valorize methane directly into ethylene. The performance of a heterogeneous catalytic process is the result of a complex interaction of phenomena at very different time and length scales. Even in the simplest reactor configurations (i.e., a packed bed reactor), conversion... Read More

Spatial amplification owing to modal instability plays a significant role in determining when and how a hypersonic boundary layer transitions from a laminar state to turbulence. Traditional stability analysis methods rely on the strong assumption of a slowly-varying baseflow, which limits their predictive power. Such methods can calculate downstream amplification only relative to upstream points where the flow has already passed through shock waves (such as a vehicle’s bow shock) and that are far away from complex geometry (such as a blunt nose tip). The estimation of perturbation amplitude... Read More

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.

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