Date of Award
11-12-2024
Publication Type
Dissertation
Degree Name
Ph.D.
Department
Mechanical, Automotive, and Materials Engineering
Keywords
Computational fluid dynamics;Electric motors;Fluid mechanics;Heat transfer;Jet impingement;Thermodynamics
Supervisor
R. Balachandar
Supervisor
K. L. V. Iyer
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Abstract
With increasing pressure for automotive manufacturers to shift from internal combustion engines to electric vehicles, comes an increasing demand to improve on-board electronics in terms of efficiency, cost and reliability. Electric motors have been subjected to rapid development over the last decade and have been able to operate with higher power densities. Managing the increasing power densities and high heat loads experienced in electric motor applications is the current bottleneck in further increasing the efficiency and continuous peak power capability of electric motors. Presently, conventional thermal management solutions such as cooling jackets and shaft cooling have reached their potential cooling limits and are no longer able to meet the increasing thermal needs of electric motors. Direct jet impingement cooling has proven to be successful for a range of heat transfer applications and has become increasingly implemented in modern electric motors. However, the behavior of cooling jets in rotational fields remain relatively unknown and has been a growing area of research. In this dissertation, jet impingement in rotational fields is numerically investigated using CFD. Firstly, the flow and heat transfer characteristics of a submerged jet impinging axisymmetrically onto a rotating disk are studied over a range of jet Reynolds numbers (1,300 to 7,900), rotational Reynolds numbers (10,000 to 175,000), and Prandtl numbers (124 to 400). In the second stage of the research, a submerged confined jet impinging asymmetrically is then studied where the mean flow and turbulence characteristics are investigated. Finally, the modeling methodology adapted in the beginning stages of the research is then applied to carry out a full-scale CFD simulation on an electric motor cooling system employing liquid jet impingement. In this stage, a wound-field synchronous motor is used to study the thermal management system and the jets are considered to be unsubmerged. From this study, it was demonstrated how parameters such as jet Reynolds number, rotational Reynolds number and Prandtl number, influence the heat transfer characteristics of jets in rotational fields. A Nusselt number correlation considering these parameters was proposed. It was shown that higher jet and rotational Reynolds numbers provide greater heat transfer rates. Moreso, the stagnation region heat transfer was sensitive to changes in the jet Reynolds number, whereas the average heat transfer was more sensitive to the rotational Reynolds number. The wall shear stress was also shown to increase (an undesired effect) as the jet and rotational Reynolds number increase, which demonstrates a trade-off between heat transfer enhancement and drag experienced by the rotating impingement surface. When a jet impinges asymmetrically, complex mean and turbulence features are observed. In general, the flow field can be jet dominated or rotation dominated. The flow field is shown to be rotation dominated when the jet fluid cannot penetrate the swirling flow induced by the rotating impingement surface. The flow field was shown to be jet dominated when the jet can completely penetrate and expand against the swirling flow. A transitional flow exists when the effects of the jet’s momentum and swirling flow are both prominent. In this type of flow, the circumferential turbulence intensities show a region of mixing between the swirling flow and the wall jet as indicated by regions of high turbulence intensities. Finally, the full-scale CFD simulation of the e-motor cooling system demonstrated how jet impingement can provide uniform cooling of the rotor windings and rotor lamination. Splashing of oil from the rotor to the stator windings provided additional cooling to the stator. Additionally, the CFD model indicated oil within the air gap is the main contributor to spin loss.
Recommended Citation
Klinkhamer, Corey, "Investigation of Cooling Jets in a Rotational Field with Application Towards Electric Motor Cooling" (2024). Electronic Theses and Dissertations. 9381.
https://scholar.uwindsor.ca/etd/9381