COMPLETE ITN - ETN NETWORK

We are delighted to announce a major achievement within the COMPLETE project. One of our Early Stage Researchers (ESR 15), Shahbozbek Abdunabiev, successfully defended his doctoral dissertation on October 18th, 2024, at the Politecnico di Torino.

This accomplishment reflects years of rigorous effort, dedication, and academic excellence. We extend our heartfelt congratulations to Shahbozbek on reaching this significant milestone.

For further details, please refer to https://drive.google.com/file/d/1yLQW2uyCpD9t9rtYsPfTVVE1qyK4os8V/view?usp=sharing

We are proud to announce that Niccolò Gallino has successfully defended his Master’s thesis for the Master’s Degree in Physics of Complex Systems on April 4, 2024.

Under the supervision of Prof. Daniela Tordella, Niccolò presented his thesis titled:

"Relative dispersion and Lagrangian correlations in inhomogeneous turbulence: experimental and numerical study"

His research investigates two fundamental and complex aspects of turbulence: relative dispersion—how particles spread within turbulent flow—and Lagrangian correlations, which track the temporal evolution of particle velocities and other properties as they move with the flow.

The study combines experimental data collected using custom-designed miniaturized radiosondes deployed in the atmospheric boundary layer with numerical simulations of cloud-edge regions using Direct Numerical Simulations (DNS). These simulations model turbulence at the boundary of clouds, tracking Lagrangian water droplets in a highly dynamic mixing layer.

Niccolò’s work critically evaluates how classical turbulence theory, particularly the Kolmogorov-Obukhov K41 framework, holds up under more realistic, inhomogeneous flow conditions. His results highlight deviations from K41 predictions, offering deeper insight into the influence of atmospheric inhomogeneities. On the numerical side, he lays the groundwork for future high-fidelity simulations capable of exploring these effects in greater depth.

The study also breaks ground in the lesser-explored area of Lagrangian correlations, providing new data both from field experiments and simulations, and extending the analysis beyond traditional velocity components to include other dynamically relevant quantities.

We warmly congratulate Niccolò Gallino on this significant achievement and commend him for his rigorous and innovative contribution to the understanding of turbulent fluid dynamics!

For more details, please see tesi.pdf

In this work we designed and developed a cluster of light expendable radiosondes that can float passively inside warm clouds to study their micro-physical processes. This involves the tracking of both saturated and unsaturated turbulent air parcels. The aim of this new kind of observation system is to obtain Lagrangian statistics of the intense turbulence inside warm clouds and of the lower intensity turbulence that is typical of the air surrounding such clouds. Each radiosonde in a cluster includes an electronic board, which is mounted onto a small, biodegradable balloon filled with a mixture of helium and air. The cluster is able to float inside clouds for a few hours and to measure air temperature, pressure, humidity and the associated position, velocity, acceleration and magnetic field readings of each radiosonde along their trajectory.

18th European Turbulence Conference, September 4-6, 2023, Valencia, Spain

We presented a newly developed methodology to track Lagrangian fluctuations of physical and chemical quantities in the atmosphere. The measurements are carried out by using a freely floating cluster of mini, innovative radiosondes. The primary aim of this method is to obtain Lagrangian statistics of the turbulence fluctuations inside warm clouds, their boundaries and the surrounding sub-saturated environmental air. This is important information, difficult to find at the state of the art and very useful for modeling cloud formations which are still a primary source of uncertainty in the numerical simulation of climatic and meteorological information.

We expand on the original studies on atmospheric diffusion shown on a distance neighbour graph, Q, by Lewis F. Richardson (1926), a quantity that effectively defines a distribution of particles over a separation distance, ℓ. Because of its definition we expect Q to evolve according to an equation of type ∂Q/∂t = ∂/∂l (F(l)∂Q/∂l). Particular emphasis was put on the search for a correct form of the diffusion function F. Richardson originally proposed an F ∼ l^(4/3) law. His studies have then been revisited by many, among which Obukhov, leading to the so-called Richardson-Obukhov l^2 ∼ t^3 theory, which holds in the homogeneous, isotropic turbulence regime. Our analysis is carried out on direct numerical simulations (DNS) of a time-decaying turbulent shear-free layer which represents a small portion of a top warm cloud boundary, a multiphase simulation where air, water vapor and water drops have been included.

The radiosonde cluster network was presented in the context of Metrology for Industry 4.0 & IoT 2023 conference on June 6-8 at Brescia, Italy.

The aim of the present work is to design and develop a remote radiosonde cluster network and receiver station based on LoRa radio communication protocol. The designed remote sensing unit, radiosonde, should be light (less then 20 gr) and expendable as much as possible. The radiosonde tracks variations of physical and chemical quantities in the surrounding environmental ambient. Primary target of this this new kind of radiosonde is to obtain Lagrangian statistics of turbulence fluctuations inside warm clouds, clear-air and cloud-clear-air mixing regions. However, the application of the sensor network is not limited and can be extended to other contexts, such as environmental monitoring over urban and industrial areas. The radiosonde is made of the radioprobe attached to a biodegradable balloon filled with a mixture of helium and air. The system is able to float inside and around clouds for a time span of the order of a few hours and measure fluctuations of air temperature, pressure, humidity position, velocity and acceleration along its own trajectory. In this manner, the system can provide a multipoint endoscopic view of the flow by following the air parcels in passive way.

Recent results have shown that there is an acceleration in the spread of the size distribution of droplet populations in the region bordering the cloud and undersaturated ambient. We have analyzed the supersaturation balance in this region, which is typically a highly intermittent shearless turbulent mixing layer, under a condition where there is no mean updraft. We have investigated the evolution of the cloud - clear air interface and of the droplets therein via direct numerical simulations. We have compared horizontal averages of the phase relaxation, evaporation, reaction and condensation times within the cloud-clear air interface for the size distributions of the initial monodisperse and polydisperse droplet populations.

We will also present results on turbulence dispersion in the cloud - clear air interface based on the distance neighbor graph statistics (Richardson, 1926) obtained by tracking water droplets in the Lagrangian framework.

Phys. Rev. Fluids 6, 114803 – Published 15 November 2021

The paper published by Marco Boetti, Maarten van Reeuwijk, and Alexander Liberzon.

Aim> Turbulent/nonturbulent interfaces typically have a thickness of the order of the Kolmogorov scale. However, when we add a density or temperature stratification, we observe that the interface thickness scales differently. We analyze two different turbulent flows at moderate Reynolds numbers using direct numerical simulation and demonstrate that the results collapse on a single curve using a lengthscale based on the potential enstrophy.

 link:

 https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.6.114803

The work was presented during the "Turbulence and Interface, PC Henri Benard Workshop" on June 15-17, Lyon, France.

The present work discusses investigation of the evolution of the cloud - clear air interface and of the droplets therein via direct numerical simulations. We have compared horizontal averages of the phase relaxation, evaporation, reaction and condensation times within the cloud-clear air interface for the size distributions of the initial monodispersed and polydisperse droplets. For the monodisperse population,a clustering of the values of the reaction, phase and evaporation times, that is around 20-30 seconds, is observed in the central area of the mixing layer, just before the location where the maximum value of the supersaturation turbulent flux occurs.