Towards the modelling of high Prandtl number liquid cooling

The recent advent of electric vehicles is pushing car manufacturers to design more compact electric motors running at higher speeds, leading to higher local heat generation. Cooling is therefore crucial to preserve the efficiency and the reliability of the electrical machine. Innovative cooling systems based on oil jets directly impacting critical parts are then considered. To design and evaluate the performance of these cooling systems, we need to estimate the heat transfer coefficients between the liquid jet and the solid parts of the engine which has complex geometries and surface states (end-windings and magnets of the rotor or the stator...).
Physically, this cooling method is characterized by fluid flow over complex surfaces with high Prandtl numbers. The modelling of high Prandtl fluids involves the resolution of a very fine thermal boundary layer, especially in the impact zone of the jet where the cooling is maximum. For liquid cooling applications, the solid surfaces impacted by the liquid film are large; the required mesh refinement to correctly estimate the heat transfer coefficient therefore involves often prohibitive calculation times.
The PhD student will contribute to this field by designing an original approach based on the development of sub-scale models to accurately evaluate heat transfers while having a coarser mesh. The objective is to develop and implement a near-wall heat transfer law suitable for low Reynolds and high Prandtl flows, as well as for smooth and complex surfaces. The numerical results will be compared to experimental data from IFPEN or from the literature. Finally, impinging jet simulations will be carried out, varying different conditions (roughness, nozzle diameter, nozzle / plate distance, liquid properties, liquid temperature, flow rate…) in order to propose a Nusselt correlation dedicated to cooling liquid jet impacting a complex surface.

Keywords: Electric machine cooling – numerical simulation – fluid mechanics – thermal transfer – near-wall heat transfer law – two-phase flows – liquid film – VOF method

• Academic supervisor    Professor, NICOUD Franck, Institut Montpelliérain Alexander Grothendieck
• Doctoral School    ED166, I2S Information Structures Systèmes, https://edi2s.umontpellier.fr/
• IFPEN supervisor    PhD, VINAY Guillaume, Numerical Modelling of Energetic Systems Department, guillaume.vinay@ifpen.fr
• PhD location    IFP Energies nouvelles, Rueil-Malmaison, France
• Duration and start date    3 years, starting in fourth quarter 2022
• Employer    IFP Energies nouvelles, Rueil-Malmaison, France
• Academic requirements    University Master degree in Fluid Mechanics
• Language requirements    Fluency in French or English, willingness to learn French
• Other requirements    C/C++ and Python programming, Linux, Scientific Computing