Modeling and Evaluation of Fluid Flow Resistance Characteristics of the Cooling Channel in the Aircraft Oil-Cooled Electric Machine

Oil cooling technique is one of the important ways to reduce the temperature rise and enhance the power density of aircraft electric machines (EMs). However, the high viscosity of the oil leads to high flow resistance, which may reduce the efficiency of the hydraulic system and damage the components. This article conducts research on the flow resistance characteristics of cooling channels. First, considering computational efficiency and accuracy, the influence of mesh type, size, and boundary layers on the cell count and calculation results is compared and summarized. Then, computational fluid dynamics (CFD) models for the series cooling channel and split-flow cooling channel are established. Another split-flow method is explored to optimize the cooling channel. Based on CFD and theoretical formulas, the influence mechanism of channel type and flow rate on flow resistance is revealed. Further, the heat-pressure ratio (HPr) is defined as an indicator to evaluate the heat dissipation capability of cooling structures. Finally, the pressure test models are constructed by 3-D printing. The experiments verify the correctness of analysis. The optimization methods can reduce flow resistance by 80.4% and increase heat transfer coefficient (HTC) by 44% at the same pressure. The HPr can serve as a reference for evaluating cooling structures.