Context

The flash boiling phenomenon occurs when a superheated liquid, maintained at a temperature above its boiling point and under high pressure, is suddenly expanded into an environment where the pressure is below its saturation pressure. This rapid depressurization causes an almost instantaneous vaporization of the liquid, leading to the disintegration of the jet into a complex two-phase mixture whose dynamics and structure are entirely governed by phase-change mechanisms (Kurschat et al., 1992). This highly transient and multiphysics flow involves a nonlinear interaction between compressible hydrodynamics, non-equilibrium thermodynamics, and heat transfer. Recent studies (Rees et al., 2019, 2020) have shown that such rapid expansion leads to a metastable thermodynamic state, followed by violent evaporation and supersonic expansion. These processes generate shock structures including Mach disk, and an unstable jet dynamic. In space applications, the presence of a surrounding vacuum during orbital phases makes systems particularly prone to this phenomenon. Examples include propellant injection prior to engine reignition, tank purges, and activation of attitude-control thrusters. These events are directly influenced by flash boiling, which affects injection dynamics, mixture formation, ignition conditions, and combustion stability. Moreover, violent vaporization may cause destructive pressure spikes capable of damaging injection system components. In this context, Large Eddy Simulation (LES), is a powerful tool for investigating and understanding the unsteady and multiphysics mechanisms associated with flash boiling. LES can explore regimes that are extremely difficult to reproduce experimentally, thereby supporting the design of next-generation cryogenic propulsion systems.

Scientific Challenges

• High-fidelity representation of multiphase flows and liquid–vapor phase transitions. 

• Complex coupling between turbulence, phase change, and non-equilibrium flow dynamic and thermodynamic (Karathanassis 2017). 

• Realistic modeling of cryogenic thermodynamic properties (hydrogen, methane, oxygen, nitrogen). 

• Cross-validation of numerical results against available experiments.

Objectives

The overall objective of this PhD is to develop, validate, and apply a multiphysics LES framework for modeling flash boiling in cryogenic jets relevant to space propulsion. This work will account for delayed evaporation effects, pressure and temperature disequilibria, and multiphase interactions within a consistent thermodynamic framework. Specific scientific objectives include:

• Analyzing the physics of flash boiling through high-fidelity LES of an evaporating jet representative of an academic experiment, and identifying flow regimes as a function of operating conditions.

• Modeling evaporation delay and investigating its influence on flow dynamics and jet structure.

• Relaxing conventional simplifying assumptions of pressure and temperature equilibrium between phases.

• Applying the developed methodology to a representative space application to evaluate the impact of delayed evaporation and interphase disequilibria on overall jet behavior. The work will rely on Large Eddy Simulations (LES) performed with the YALES2 CFD placorm, developed at CORIA. YALES2 is a massively parallel, multi-scale, multiphysics CFD code that has already demonstrated excellent results in modeling compressible single-phase (Tene Hedje et al., 2023, 2024) and two-phase (Carmona, 2025) flows with shocks.

Work Plan

Year 1

• Comprehensive literature review on flash boiling, non-equilibrium models, and phasechange mechanisms. Simulation of the flash boiling of a liquid jet

• High-fidelity LES of a experimental evaporating jet configuration using equilibrium models (Lamanna et al., 2014, 2015; Rees et al., 201ti, 2020).

• Analysis of the influence of operating conditions on observed regimes.

• Development of an evaporation-delay model to capture metastable thermodynamic states and assessment of its impact on flow dynamics. 

Year 2

• Development of a non-equilibrium model for pressure and temperature disequilibria compatible with unstructured meshes, allowing application to complex geometries (including adaptation of numerical schemes and boundary conditions).

• Study of the impact of interphase disequilibria, especially exchange term modeling, on the two-phase jet behavior investigated during Year 1.

Year 3

• Application of the complete methodology to a representative space case (cryogenic injection in partial vacuum).

• Manuscript writing and thesis defense.

Expected Outcomes

- Fundamental advances in understanding out-of-equilibrium two-phase flows.

- Development of a comprehensive numerical model including pressure, temperature, and thermodynamic disequilibria (evaporation delay) for simulating flash boiling in complex configurations under space conditions.

- Enhancement of simulation tools for designing next-generation cryogenic injectors, feed lines, and nozzles for future rocket engines.

Work environment

Founded in 1967, CORIA (Complexe de Recherche Interprofessionnel en Aérothermochimie) is a joint research unit affiliated with the CNRS Institute of Engineering and Systems (INSIS), the University of Rouen Normandy, and the Rouen Normandy Institute of Applied Sciences (INSA). The laboratory, which has a staff of approximately 170, is located on the Madrillet Science and Engineering Campus near Rouen, in Normandy. CORIA has internationally recognized expertise in the modelling of turbulent reactive and non-reactive flows, including two-phase flows. Its research activities cover a wide range of topics such as turbulent mixing, combustion, plasmas, as well as optics and laser diagnostics. The laboratory combines theoretical approaches, physical modelling, high-fidelity numerical simulations, and experiments conducted at different scales. For many years, CORIA has been developing YALES2, a massively parallel Large Eddy Simulation (LES) software dedicated to high-performance computing. This simulation platform is developed and used by a broad international community of researchers and engineers in computational fluid dynamics, and has demonstrated strong capabilities for the simulation of complex turbulent, reactive, and two-phase flows.

General information

• 3-year PhD thesis, at the CORIA laboratory, Rouen, France

• Salary: approx. €1,700 net/month

• Contract start date: september 2026

• Funding: 50% CNES, 50% Normandy Region

• Contact: Julien CARMONA (julien.carmona@coria.fr)

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For more Information about the topics and the co-financial partner (found by the lab!); contact Directeur de thèse - guillaume.ribert@coria.fr

Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online before March 13th, 2026 Midnight Paris time!

The applicant must have a Master's-level degree in Mechanics or Energy, with a background in fluid mechanics, aerodynamics, multiphase Flows, thermodynamics, scientific calculation and CFD. Good oral and written communication skills in English are also required for presenting at conferences and writing scientific publications.