Investigation of thermo-hydraulic oscillation phenomena in two-phase heat exchangers – Applications to space propulsion systems

Thermal systems play a central role in energy and propulsion technologies, particularly in sectors subject to stringent performance, reliability, and operational safety requirements such as aerospace and space applications. In these fields, heat exchangers are essential components for thermal management and energy flow control.

ArianeGroup, a global leader in civil and military space propulsion, develops and operates complex thermal systems under extreme pressure, temperature, and heat flux conditions. Within this context, the company has a particular interest in thermo-hydraulic phenomena occurring in heat exchangers operating under two-phase (liquid-vapor) flow conditions, especially those used in launcher engine cooling circuits and cryogenic systems.

These two-phase systems are prone to thermo-hydraulic oscillations (flow instabilities, pressure oscillations, and temperature fluctuations) resulting from the complex interaction between heat transfer, phase change processes, and flow dynamics. Such instabilities may degrade thermal performance, reduce operating margins, induce additional mechanical stresses, and, in some cases, compromise overall system reliability.

General objective of the PhD

The primary objective of this PhD project is to characterize, understand, and model the physical mechanisms responsible for thermo-hydraulic oscillations in a heat exchanger operating under two-phase flow conditions. The research will aim to identify the conditions leading to the onset of these instabilities, analyze their dynamics, and propose solutions to mitigate or control them, while remaining consistent with the industrial constraints of space propulsion systems.

Scientific Objectives and Technological Challenges

The PhD project will be structured around the following research areas:

1. Experimental Investigation

Design and implement an experimental facility representative of a two-phase heat exchanger.

Instrument the system to accurately measure key parameters (mass flow rate, pressure, temperature, and void fraction).

Identify and characterize the various thermo-hydraulic oscillation regimes as a function of operating parameters (heat flux, pressure, inlet conditions, geometry, and heater configuration).

Analyze the nature of the observed instabilities (frequencies, amplitudes, thermal-hydraulic coupling mechanisms).

2. Modeling and Numerical Simulation

Develop appropriate physical models (1D, quasi-1D, or simplified CFD models) capable of reproducing experimentally observed phenomena.

Perform numerical simulations to predict the dynamic behavior of two-phase systems.

Compare and validate the models against experimental data.

Identify the dominant parameters and physical mechanisms responsible for the instabilities.

3. Optimization and Design Recommendations

Investigate the influence of heat exchanger design parameters (geometry, pressure losses, volumes, and boundary conditions) on thermo-hydraulic stability.

Propose improvement strategies such as design modifications, passive stabilization devices, or active control approaches.

Assess potential gains in terms of performance, robustness, and reliability of thermal systems.

4. Expected Outcomes

This PhD project will contribute to the scientific understanding of thermo-hydraulic instabilities in two-phase flow systems while addressing practical industrial challenges associated with the design and operation of space propulsion systems. The results will be disseminated through scientific publications, heat exchanger design recommendations, and the enhancement of modeling and simulation tools.

Academic and Industrial Framework

This PhD project will be carried out within a partnership between ArianeGroup and the Lafset Laboratory (Laboratory for Refrigeration, Energy and Thermal Systems) of the Conservatoire National des Arts et Métiers (Cnam), which will provide the academic supervision and administration of the doctoral program.

Within ArianeGroup, the Functional Engine Systems and Combustion departments will contribute their expertise in fluid dynamics, as well as provide access to state-of-the-art experimental facilities and advanced simulation tools.

The Lafset Cnam conducts internationally recognized research in the fields of refrigeration, energy systems, heat transfer, thermo-hydraulics, and two-phase flows. The laboratory has extensive expertise in experimental analysis and modeling of complex thermal systems, particularly for industrial applications involving significant energy and technological challenges.

The research activities will be primarily conducted at the ArianeGroup site in Vernon, France, with regular interactions with Cnam researchers.

Travel will be required between the ArianeGroup site in Vernon, the Cnam campus in Paris, and the experimental test facility located near Rouen.

The Laboratory for Refrigeration, Energy and Thermal Systems (Lafset) is a research group with long-standing expertise in thermal and refrigeration systems. Its research activities focus on advancing the understanding of fundamental physical processes, particularly heat and mass transfer phenomena, through detailed investigations of working fluids and two-phase heat exchangers. The laboratory also develops advanced yet practical methodologies for the analysis, optimization, and performance enhancement of energy systems under real operating conditions.

The ideal candidate for this PhD position should possess the following qualifications:

Academic Background:  Master’s degree (or equivalent) in Thermal Engineering, Energy Engineering, Process Engineering, or a related field.

Technical Skills: Strong knowledge of thermodynamics, fluid dynamics, and numerical simulation methods.

Experimental Experience: Previous experience in experimental work and data processing.

Programming Skills: Proficiency in programming languages such as Python, MATLAB, or C++.

Languages: Good command of English, both written and spoken.