Coloquio: Disipación e intermitencia en estelas turbulentas

Martin Obligado
Centrale Lille Institut

The study of turbulent flows continues to challenge researchers. For instance, within the global effort to increase the generation of alternative energy, the study of the flow downstream of one or multiple turbines has drawn significant attention from the turbulence community due to its complexity. It involves turbulent wakes, their interactions, and their coupling with the background turbulent flow.

Many recent advances in the modelling of turbulent flows have yet to be adapted for such studies. To advance this research, a deeper understanding of the inner structure of turbulence, the energy cascade, is required. This phenomenon governs how energy is transferred from large to small scales and how it is ultimately dissipated. It has been found to play a crucial role in defining key properties of turbulent wakes, such as their velocity deficit and their streamwise spreading behaviour.

In this seminar, I will discuss recent advances in turbulence research, particularly relevant to wind energy applications. I will present experimental and theoretical evidence demonstrating the existence of a non-canonical energy cascade observed across a broad range of flows, including grid turbulence, turbulent boundary layers, and the turbulent axisymmetric wake. I will explore how this alternative cascade may result in turbulent wakes exhibiting scaling laws different from those predicted by standard models, such as the Richardson–Kolmogorov cascade. Moreover, I will illustrate how an oscillating freestream velocity influences this effect, as dissipation follows a hysteresis cycle linked to the unsteady term in the Kármán–Howarth equation.

Furthermore, I will introduce a newly discovered empirical law relating the energy cascade to small-scale intermittency in turbulent wakes and other inhomogeneous flows. Our findings, based on an extensive range of flows and experimental conditions, reveal a relationship between the dissipation constant, which characterises the energy cascade, and the intermittency factor, which quantifies deviations from self-similarity within the inertial range. Interestingly, while no prior theoretical expectation exists for a direct correlation between these two parameters, our results show that one evolves as the inverse of the other, potentially establishing a new universal law for turbulent flows.

Serge Haroche: The laser in quantum science

SERGE HAROCHE
Collège de France, Paris.  Premio Nobel 2012

This year marks the 100th anniversary of quantum mechanics. Among all the inventions born of this physics, the laser occupies an important place, both for the lineage of discoveries that led to its birth, and for the role it plays today in fundamental and applied science. It has opened up fields in research that could not have been imagined at the time it was invented. We owe to it the cooling and trapping of atoms, the study of quantum gases of bosons and fermions, the discovery of gravitational waves and the manipulation of individual quantum particles which has led to current research into quantum simulation and quantum computing. The laser may also provide answers to fundamental questions about the physics beyond the Standard Model or about the nature of the hypothetical dark matter. The history of the laser in blue sky science illustrates the passion for precision and the essential link between basic research and technological advances that have driven modern science since its advent in the Age of Enlightenment.

Coloquio: Dimensionalidad y transiciones en flujos turbulentos

Patricio Clark Di Leoni
Universidad de San Andres; CONICET

Los fluidos pueden realizar desde dinámicas laminares de baja dimensión hasta dinámicas turbulentas de muy alta dimensión. Los procesos que dominan esta transición siguen generando grandes interrogantes y preguntas abiertas. A través de una combinación de métodos de machine learning y análisis de Lyapunov logramos generar estimaciones precisas de la dimensionalidad de distintos flujos a lo largo de un amplio rango de parámetros. En esta charla mostraremos como los cambios en la dimensionalidad aportan una nueva y fructífera forma de estudiar el problema de la transición en fluidos.

Coloquio: Estimulación periódica en redes de señalización y regulación genética

Alejandra Ventura
Departamento de Física e IFIByNE (UBA-CONICET)

Los sistemas de señalización celular y regulación génica procesan información mediante dinámicas complejas que responden a estímulos externos. Si bien su comportamiento ante estímulos constantes es bien conocido, las respuestas a señales periódicas, especialmente en etapas transitorias, han sido poco exploradas. Aquí mostramos que la estimulación periódica puede cumplir funciones distintas en diferentes niveles de regulación. En redes simples, identificamos preferencias de frecuencia que emergen transitoriamente y desaparecen en el régimen estacionario. En redes postranscripcionales, observamos que la síntesis pulsátil de microARNs potencia la represión de sus blancos de modo dependiente de la frecuencia. En conjunto, estos resultados revelan que las respuestas transitorias y la pulsatilidad son mecanismos generales mediante los cuales las células filtran y codifican información temporal.