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Job Record #18971
TitleHydrogen explosions in porous media: experiments & simulations
CategoryPhD Studentship
EmployerCommissariat à l'Energie Atomique - CEA Saclay - STMF
LocationFrance, Saclay
InternationalYes, international applications are welcome
Closure Date* None *
# Full information with illustrations here

# Context

A future asset for the low-carbon transition, hydrogen remains a leading 
scientific and security challenge. Colorless and odorless, hydrogen leaks 
easily, ignites at low concentrations and temperatures, and can lead to the 
spread of rapid deflagrations as well as detonations, which are a dangerous type 
of supersonic combustion. Understanding the transition mechanisms from 
deflagration (slow flame) to detonation (supersonic flame accompanied by a 
sudden shock wave) is therefore essential for securing hydrogen production 
installations (electrolyzers) as well as for nuclear industry. Indeed, in the 
accident scenario of loss of cooling and melting of the core of a reactor, the 
oxidation of the uranium rod cladding can lead to the release of hydrogen. It 
was the subsequent explosion that led to the loss of containment and the release 
of radioactive materials at Fukushima and Three Mile Island. Controlling the 
hydrogen risk is therefore one of the major challenges of nuclear safety.
The main mechanism of the deflagration -> detonation transition is the presence 
of obstacles along the flame path. These will generate vorticity, which 
increases the surface area of the flame and accelerates the reactive wave. When 
the number and size of the obstacles is sufficient, a runaway effect and wave 
reflections can lead to a shock-chemical reaction coupling: the detonation is 
born, propagating at several kilometers per second. Unfortunately, we cannot 
avoid that industrial installations are cluttered with obstacles: pipes, 
buildings, machines, walkways, structures… and present this type of scenarios.

Conversely, a very heavily congested porous medium can, on the contrary, smother 
a flame that is too rapid and allow the reverse transition detonation -> 
deflagration, of a less dangerous nature. For example, we see that a detonation 
can be attenuated by passing through a porous matrix (see refs. [1,3]), or when 
a porous medium is placed along the walls during detonation. propagation in a 
tube [4,5]. A crucial safety question then arises: under what circumstances does 
an obstacle accelerate or slow down a flame? Can we design porous media that 
stop dangerous flames?

# Goals
This thesis work aims to address this question from three angles:
-	on the one hand, via the preparation and carrying out of experimental 
testson the hydrogen explosion test bench at CEA Saclay (SSEXHY, see Fig. 3). 
Among others, these are:
-	to explore different geometries for porous media, based on configurable 
topologies. For example, we could take inspiration from Triply Periodic Minimal 
Surfaces (TPMS) type functions. These porous matrices will then be 3D printed 
via metal additive manufacturing (316L stainless steel);
-	to prepare the instrumentation of the SSEXHY explosion test bench 
equipped with a visualization section via a Schlieren technique coupled with an 
ultra-fast camera at several million images per second;
-	to post-process the results of shock sensors, pressure sensors and 
photomultipliers equipped with an OH* filter.
-	on the other hand, via numerical simulations of the DNS or LES type on 
search calculation codes: an internal CEA/CNRS code (DRYADS) developed during 
the CEA thesis of Luc Lecointre [1], and a CERFACS code (AVBP) well known in the 
combustion community. For example, we could be interested in:
-	the influence of the geometry of porous obstacles (shape, porosity, 
hydraulic diameter, etc.) on the speed of flame propagation and the 
deflagration<->detonation transitions;
-	the influence of the 2/3D character of the porous materials;
-	the proposal of new criteria for choosing the level of mesh refinement 
for capturing the phenomena of interest;
-	testing new temporal integration schemes for diffusion and reaction 
-	to the participation and testing of the porting of the DRYADS code in 
C++ on a new HPC platform (samurai), developed by the CMAP laboratory of the 
Ecole Polytechnique.

-	finally, a theoretical modeling of the problem from the point of view of 
volume-averaged equations can be carried out, with the objective of developing 
simplified and predictive models on the behavior of porous flame arresters.
This thesis is a continuation of a nearby internship focused on 2D digital 
simulations, offered in 2024 and which can be linked to the thesis subject as a 
preparatory internship (subject available on the INSTN website or contact the 
supervisors for more information). information).

# Work environment

The internship will take place at the CEA center in Saclay within the LE2H 
experimental laboratory (formerly LIEFT).

# Skills required or desired

Demonstrated physical acumen, mathematical and modeling skills, knowledge of 
numerical schemes/methods, foundation in C++ and Python programming. Knowledge 
of compressible fluid mechanics and combustion would be a plus.

# Required profile

-	Master 2 or equivalent in fluid mechanics;
-	Curiosity about fundamentals, interest in experimental and ideally in 
digital simulation;
-	Rigorous, involved, passionate.

# References

[1] Lecointre, L. (2022). Hydrogen flame acceleration in non-uniform mixtures. 
Doctoral thesis from the University of Paris-Saclay.
[2] Lecointre, L., Vicquelin, R., Kudriakov, S., Studer, E., Tenaud, C. (2022). 
High-order numerical scheme for compressible multi-component real gas flows 
using an extension of the Roe approximate Riemann solver and specific 
Monotonicity-Preserving constraints. Journal of Computational Physics, 450: 
[3] Radulescu, MI, & Maxwell, BM (2011). The mechanism of detonation attenuation 
by a porous medium and its subsequent re-initiation. J. Fluid Mech., 667, 96-
[4] Teodorczyk, H., and JHS Lee. (1995) Detonation attenuation by foams and wire 
meshes lining the walls, Shock Waves 4:225–236.
[5] Radulescu, R., and JHS Lee. (2002). The failure mechanism of gaseous 
detonations: experiments in porous wall tubes, Combust. Flame 131:29–46.

Contact Information:
Please mention the CFD Jobs Database, record #18971 when responding to this ad.
NamePierre-Alexandre MASSET
Email ApplicationYes
Record Data:
Last Modified16:17:40, Wednesday, January 31, 2024

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