Numerical modelling of stepped helical cooling channels

Abstract

The automotive industry is in the midst of a radical change of propulsion technology to meet the increasingly stringent limits on emissions and fuel consumption. Electric and hybrid power-trains are progressively replacing their internal combustion counterparts, as they are more efficient, especially in transient operation. In electric and hybrid vehicles effective cooling system operation is of utmost importance as it influences directly the efficiency and power density levels achievable by the power train. Thus, accurate analyses are needed to maximize the thermal performance of these systems. In this work an electric motor cooling jacket, that features a stepped helical geometry, is studied by means of CFD, with a particular focus on the head losses. The periodicity of the cooling channels geometry along the helical development is exploited to reduce the computational domain to a basic periodic module. The flow field is determined by applying a 3D Finite Volume approach, and numerical solutions are obtained by means of a validated incompressible solver. Novel boundary conditions are purposely developed to allow for the coupling of the inlet and outlet patches, which are roto-translated with respect to each other. The sensitivity of integral results on friction losses, with respect to the number of periodic modules included in the model, is investigated. The developed numerical model is employed to obtain a suitable correlation for the equivalent Darcy friction factor as a function of the Reynolds number only. Finally, a first estimation of the total head losses is obtained by using the Darcy Weisbach formula along with the aforementioned friction factor correlation.