Numerical Analysis of the Local Heat Transfer Coefficient in a Rotating Hollow Rotor Shaft Liquid Cooling System for Electric Traction Motors

This paper presents the fluid flow and local heat transfer coefficient associated with a rotating liquid hollow rotor shaft cooling system for electric traction motors. Computational fluid dynamics (CFD) is utilized to simulate the fluid flow and heat transfer phenomena to obtain the local heat transfer coefficient. A comparison is conducted between a stationary and a rotating hollow rotor shaft cooling system using 50/50 ethylene glycol water mixture. The shaft rotation is found to alter the fluid flow through the development of vortices and a secondary flow due to the Coriolis and centrifugal effect. The alteration of the fluid flow is found to enhance the fluid turbulence, significantly increasing the local heat transfer coefficient when compared to the non-rotating case. This results in a significant decrease in the maximum operating temperature of the shaft surface. It is concluded that the local heat transfer coefficients change significantly along the length of the hollow shaft resulting in non-uniform temperature distributions. This can allow for the identification of regions of low thermal performance within the cooling system.