POROus media: Life and dEath of their wAves and Flames

Project Information

POROLEAF

Grant agreement ID: 101103502

DOI

10.3030/101103502

EC signature date 31 August 2023

Start date 1 January 2024

End date 31 December 2028

Funded under

• European Research Council (ERC)

Total cost

€ 1 499 942,00

EU contribution

€ 1 499 942,00

Coordinated by

OFFICE NATIONAL D'ETUDES ET DE RECHERCHES AEROSPATIALES
France

Periodic Reporting for period 1 - POROLEAF (POROus media: Life and dEath of their wAves and Flames)

Reporting period: 2024-01-01 to 2026-06-30

Summary of the context and overall objectives of the project

The project focuses on investigating the interactions between waves, turbulence, and combustion within porous media, with the ultimate goal of developing novel energy conversion systems that are more efficient and stable than conventional solutions. A central question driving this research is how the geometry and topology of porous structures influence the behavior of complex flows and reactive processes within them. Gaining a deep understanding of these functional relationships is expected to enable the design of compact energy systems that leverage porous media with tailored or even functionally graded properties, thereby significantly enhancing energy conversion performance.

One of the main challenges lies in the intrinsic complexity of each individual physical phenomenon—acoustics, turbulence, and combustion—while simultaneously accessing detailed flow field information inside porous media under turbulent and reactive conditions is extremely difficult.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

To address the challenges described above, the project’s first phase (spanning two years) was dedicated to studying each physical process independently within porous media. This strategy was designed to establish the foundational knowledge required to then investigate their coupled interactions.

During this phase, we carried out experimental campaigns in an impedance tube and an aeroacoustic duct to investigate, respectively, the nonlinear behavior of porous plates and the interactions between turbulence and acoustics. These studies led to a breakthrough in the understanding and modeling of aeroacoustic liners, resolving a long-standing question within the liner community and opening a new research avenue that is currently being pursued in the second phase of the ERC project.

In parallel, we performed detailed, high-resolution, pore-resolved three-dimensional simulations of turbulent flows in porous media. These simulations revealed the complex evolution of turbulence as the flow enters and propagates through porous structures, highlighting progressive adaptations in anisotropy, characteristic length scales, and turbulence intensity.

We also conducted detailed simulations of laminar reactive flows in simplified two-dimensional porous configurations to investigate flame dynamics within porous media and how these dynamics are influenced by flow conditions and porous geometry.

To support these investigations, we designed and developed from scratch new experimental modules dedicated to the study of turbulent flows and reactive flows in porous media.

Finally, we implemented advanced turbulence analysis tools (turbulence generation and kinetic turbulence energy budget co-processing) within a Lattice Boltzmann Method (LBM) solver, enabling very large-scale simulations to be performed in Phase 2 of the ERC project using this fast, GPU-accelerated computational framework.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The first breakthrough concerns new insights into the nonlinear behavior of acoustic liners subjected to high sound pressure levels. Through dedicated experiments and the development of a novel time-domain analysis applied to complex multitone signals, we demonstrated that the root-mean-square velocity is not an appropriate quantity to characterize this nonlinearity. Instead, the local particle velocity was identified as the relevant governing parameter.

A direct extension of this finding relates to the evolution of liner impedance in the presence of a grazing flow. While it has long been observed that increasing flow speed alters the impedance of acoustic liners, the underlying physical mechanisms remained poorly understood. By leveraging the newly identified nonlinear behavior of liners, we established a previously unexplored link between turbulence and acoustics over perforated plates. This connection opens a new research direction and may provide the missing key to understanding liner behavior under realistic flow conditions.

The studies on turbulence and combustion are more recent, having started during the second year of the project. Nevertheless, the ongoing numerical investigations have already yielded novel results that have been published or are currently under publication. In particular, we examined the influence of pore topology on the so-called pore prevalence scale hypothesis, which states that turbulent eddies in porous media cannot exceed the characteristic pore size. Our results show that this hypothesis holds in triply periodic minimal surface porous media, but only after the flow has passed through a previously unidentified adaptation region. This transition zone had not been described before and remains the focus of ongoing investigation.

Interestingly, our results suggest the emergence of a form of universality in turbulence within triply periodic porous media, whereby key turbulence characteristics converge toward similar values regardless of upstream conditions. These findings point toward a potentially fundamental behavior of turbulence in such media. We believe that this work is on the verge of a breakthrough, and detailed analysis is currently intensifying at the beginning of Phase 2 of the ERC project.