Yann Bartosiewicz
Recent publications

obtained his PhD in mechanical engineering from U. of Sherbrooke, Canada in 2003. After a position of research scientist at Natural Ressources Canada, he joined UCL in september 2005 as assistant professor. Since 2013 he is associate professor at UCL in the division of thermodynamics and fluid mechanics (TFL) which he lead between 2012-2016. His teaching duties include thermodynamics, thermal cycles and nuclear thermal-hydraulics. He is also an academic member of the Belgian Nuclear Education Network (BNEN) which he chaired between 2012-2016.

His research interest covers numerical simulation and experiment in thermodynamic, fluid mechanics and heat transfer for applications in energy systems and nuclear thermal-hydraulics.

For energy systems his research focusses on the investigation of supersonic ejectors to be used in waste heat recovery technologies as well as two-phase ejectors to be used in heat pumps. Those investigations are carried out at the component scale by as well as at the system scale. In both cas a balance is achieved between numerical simulations (CFD, system modeling) and experiments (local flow measurement/visualization within an ejector and full system experiment). In this field the collaborations includes Natural ressources Canada, University of Sherbrooke, Georgia Institute of Technology, University of Firenze, EDF (Electricité De France), Polish academy of sciences.

For nuclear thermal-hydraulics, the research is essentially conducted by numerical simulation. The main research topic concerning GENII/GENIII reactors is the simulation of two-phase choking occurring during the flashing of a liquid (application to a Loss of Coolant Accident) other two-phase flows situation related to safety. For future reactors (GENIV) the research is focussed on the simulation of turbulent heat transfer in liquid metals under different conditions; this includes direct numerical simulations (DNS), Large-Eddy Simulation (LES) and Reynolds Averaged Simulation (RANS). This research in thermal-hydraulics is essentially achieved through the participation in EU projects with many collaborators (EDF, CEA, NRG, SCK•CEN, VKI, etc.).

Research group(s): TFL

PhD and Post-doc researchers under my supervision:

Wall modelling in Large-Eddy Simulations, with application to supersonic ejectors
Romain Debroeyer

The goal of this research is to perform high fidelity Large-Eddy Simulations (LES) of supersonic ejectors. These simulations will give a better understanding of the unsteady phenomena occurring in the ejector and how it transitions from on to off-design operation. Wall models for those LES simulations will be implemented so as to decrease the number of grid points required and hence decrease the simulation time.

CFD modeling of a transcritical CO2 ejector integrated in a heat pump
Antoine Metsue

Carbon dioxide (CO2) is an appropriate replacement for conventional refrigerants due to its limited impacts on climate change. However, the transcritical CO2 compression cycle has a low thermodynamic performance due to large expansion losses. An ejector is a favorable device which enables the use of CO2 and other environmentally friendly refrigerants. It helps to reduce losses by recovering part of the expansion work in a throttling process and improve the efficiency of the system.

The main objective of the proposed research is to develop numerical tools that will enable to (i) have an efficient/rapid methodology to design and to achieve a parametric study of a CO2 ejector to be incorporated in a refrigeration/heat pump cycle, (ii) deeply analyze the transport phenomena occurring in two-phase ejectors to improve our knowledge of the flow physics and its role in their performance.

In order to fulfill these objectives, the numerical approach will rely on a multiscale approach, i.e. 1D or thermodynamic models, Reynolds-Averaged Navier-Stokes (RANS) models, and high fidelity simulations such as Large Eddy Simulations (LES). Indeed the first approach (1D) is necessary to have a first rough idea of the design for a specific application, while the second (RANS) approach allows to get a good average, yet local, description of the internal flow field and to perform parametric analysis; this approach also gives the opportunity to develop the diagnosis tools to investigate transport phenomena. The last approach (LES) gives a total description of the flow, including turbulent fluctuations and a complete resolution of the large scale structures responsible of the mixing.

Finally the overall methodology should be tested on a real case; in this regards, it is foreseen to use the developed tools to design and test a CO2 ejector to be integrated within a large scale industrial experiment.

Vincenzo Scappaticci

Reconciling engineering models of ejectors with experiments and CFD using physics-informed machine learning
Jan Van den Berghe

Although Computational Fluid Dynamics (CFD) have proven sufficiently accurate to analyse the complex flow fields in ejectors, their computational cost remains too high to drive the design and optimization phases at system scale operation.

In that case, Lumped Parametric Models (LPM) are vastly preferable because of their lower computational cost. LPM models are based on integral balances and usually 0D formulations from isentropic gas dynamics. However, the lumping of complex physical phenomena such as turbulent mixing, oblique shock patterns and shock-boundary layer interaction into LPMs requires several closure parameters such as isentropic efficiencies. Moreover, LPMs are designed to predict global quantities such as the entrainment ratio or efficiency but are unaware of the stream-wise evolution of local parameters such as velocity, pressure, or Mach number, which only CFD can access. Finally, none of the LPMs presented in the literature consider the problem of modelling ejectors in transient conditions, which can be of primary importance at system scale operation.

This thesis aims to bridge the gap between classic LPMs and CFD approaches by introducing a new family of self-calibrating 1D models that use physics informed machine learning. In particular, the proposed models will combine 1D and unsteady gas dynamics with closure parameters that depend on local variables and properties. The functional relation linking closure models and flow parameters will be encoded in the form of Artificial Neural Networks (ANNs), and their calibration (i.e., the training of the ANN) will be automatic and online, i.e., while data is progressively collected. The model and the automated calibration procedure will be tested on experimental and numerical data. Hence the machine learning techniques will be used here to help the physical model to be closed, i.e., where our knowledge of the governing equations reaches its limit to derive universal relations for exchange of mass, momentum and energy in complex situations.

Recent publications

See complete list of publications

Journal Articles

1. Croquer, Sergio; Poncet, Sébastien; Moreau, Stephane; Lamberts, Olivier; Bartosiewicz, Yann. Large Eddy Simulation of a Supersonic Air Ejector. In: Applied Thermal Engineering, (2022). (Accepté/Sous presse).

2. Fiore, Matilde; Koloszar, Lilla; Fare, Clynde; Mendez,Miguel Alfonso; Duponcheel, Matthieu; Bartosiewicz, Yann. Physics-constrained machine learning for thermal turbulence modelling at low Prandtl numbers. In: International Journal of Heat and Mass Transfer, (2022). (Accepté/Sous presse).

3. Metsue, Antoine; Debroeyer, Romain; Poncet, Sébastien; Bartosiewicz, Yann. An improved thermodynamic model for supersonic real-gas ejectors using the compound-choking theory. In: Energy, Vol. 382, no. 111362 (2021). doi:10.1016/

4. Duponcheel, Matthieu; Bartosiewicz, Yann. Direct Numerical Simulation of Turbulent Heat Transfer at Low Prandtl Numbers in Planar Impinging Jets. In: International Journal of Heat and Mass Transfer, Vol. 173, no. 121179 (2021). doi:10.1016/j.ijheatmasstransfer.2021.121179.

5. Croquer, Sergio; Yang, Yu-Fang; Metsue, Antoine; Bartosiewicz, Yann; Poncet, Sébastien. Compound-Choking Theory for Supersonic Ejectors Working with Real Gas. In: Energy, Vol. 227, no. 120396 (2021). (Accepté/Sous presse).

6. Bartosiewicz, Yann. High fidelity simulations in support to assess and improve RANS for modeling turbulent heat transfer in liquid metals: The case of forced convection. In: Nuclear Engineering and Design, Vol. 382 (2021). doi:10.1016/j.nucengdes.2021.111362.

7. Croquer, Sergio; Fang, Yu; Metsue, Antoine; Bartosiewicz, Yann; Poncet, Sébastien. Compound-choking theory for supersonic ejectors working with real gas. In: Energy, Vol. 227 (2021). doi:10.1016/

8. Martin, J.; Ruyer, P.; Duponcheel, Matthieu; Bartosiewicz, Yann. A first experimental study of the gravity-driven flashing of superheated water in a heated pool. In: International Journal of Heat and Mass Transfer, (2021). (Soumis).

9. De Lorenzo, M.; Pantono, A.; Pelanti, M.; Seynhaeve, Jean-Marie; Di Matteo, Michele; Lafon, P.; Bartosiewicz, Yann. A hyperbolic phase-transition model coupled to tabulated EoS for metastable two-phase flows. In: Nuclear Engineering and Design, (2021). doi:10.1016/j.nucengdes.2020.110954.

10. Angielczyk, W.; Bartosiewicz, Yann; Butrymowicz, D. Development of delayed equilibrium model for CO2 convergent-divergent nozzle transonic flashing flow. In: International Journal of Multiphase Flow, Vol. 131, no. 103351 (2020). doi:10.1016/j.ijmultiphaseflow.2020.103351.

Conference Papers

1. Debroeyer, Romain; Toulorge, Thomas; Rasquin, Michel; Winckelmans, Grégoire; Bartosiewicz, Yann. Wall-resolved LES of turbulent flow in a supersonic nozzle. 2021 xxx.

2. Metsue, Antoine; Debroeyer, Romain; Poncet, Sébastien; Bartosiewicz, Yann. An improved thermodynamic model for supersonic ejectors. 2021 xxx.

3. Metsue, Antoine; Bartosiewicz, Yann; Poncet, Sébastien. Investigation on Ejector Design for CO2 Heat Pump Applications Using Dymola. 2021 xxx.

4. Bartosiewicz, Yann. High Fidelity Simulations in Support to Assess and Improve RANS for Modeling Turbulent Heat Transfer in Liquid Metals: the Case of Forced Convection. 2020 xxx.

5. Buckingham, S.; Koloszar, L.; Villa Ortiz, A.; Bartosiewicz, Yann; Winckelmans, Grégoire. LES investigation of Prandtl number effects over a backward facing step and consequences in terms of best practice guidelines for RANS. 2019 xxx.

6. Bartosiewicz, Yann. Reconciling FCD and thermodynamics to understand transfer in supersonic ejectors. 2019 xxx.

7. Buckingham, Sophia; Koloszar, L.; Villa Ortiz, Agustin; Bartosiewicz, Yann; Winckelmans, Grégoire. LES Investigation of Prandtl Number Effects over a Backward Facing Step and Consequences for best Prtactice in Rans. 2019 xxx.

8. van Tichelen, K.; Jäger, W.; Schaub, T.; Koloszar, L.K.; Ortiz, A.V.; Planquart, P.; Narayanan, C.; Shams, A.; Roelofs, F.; Tiselji, I.; Oder, J.; Bartosiewicz, Yann; Duponcheel, Matthieu; Niceno, B.; Guo, W.; Stalio, E.; Angeli, D.; Buckingham, Sophia. A Collaborative Effort Towards the Accurate Prediction of Flow and Heat transfers in Low-Prandtl Fluids. 2019 xxx.

9. Duponcheel, Matthieu; Bartosiewicz, Yann. Direct Numerical Simulations of Low-Prandtl Turbulent Heat Transfer in Planar Impinging Jets. 2019 xxx.

10. Fang, Yu; De Lorenzo, Marco; Lafon, Philippe; Poncet, Sébastien; Bartosiewicz, Yann; Nesreddine, Hakim. Fast and accurate CO2 properties calculation algorithm for massive numerical simulations of supersonic two-phase ejectors. 2018 xxx.

Book Chapters

1. Bartosiewicz, Yann; Duponcheel, Matthieu. Large Eddy Simulation: Application to Liquid Metal Fluid Flow and Heat Transfer. In: Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors , Woodhead Publishing, 2018. 9780081019818. xxx xxx. doi:10.1016/B978-0-08-101980-1.00017-X.