Visualization of the two-phase flow in the air gap of an optically accessible generic electric motor and its effect on torque

IF 2.3 3区 工程技术 Q2 ENGINEERING, MECHANICAL
A. Auernhammer, S. Schary, A. Dreizler, B. Böhm
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引用次数: 0

Abstract

Electric motors with high-power densities are required for the implementation of electromobility. To achieve this, direct liquid cooling methods are increasingly being considered, in which oil is injected into the motor compartment. This results in a two-phase flow that can be used for efficient cooling. However, the oil, which can also penetrate the air gap between the rotor and stator, can also lead to additional losses due to increased friction. Since little is known about the two-phase flow in such systems, especially in the air gap, it is investigated by means of simple optical visualizations and high-speed laser-induced fluorescence imaging as well as torque measurements. The measurements are carried out in the air gap of an optically accessible generic model of a directly cooled electric motor. Speed variations were performed from 100 to 2000 rpm, and three different two-phase flow regimes were observed. At low speeds (Flow Regime 1), the air gap is filled locally with oil in radial direction, in the medium speed range (Flow Regime 2) with foam, while at high speeds (Flow Regime 3) separated films were observed on the rotor and stator. The torque difference between the two-phase and single-phase operation, which quantifies the mechanical losses due to the injected oil, increased continuously due to the oil in the air gap until it reached a maximum in Flow Regime 2 due to foam formation. In Flow Regime 3, the torque difference was negative. This was attributed to the fact that the grooves in the stator were filled with oil, thus reducing the turbulence generation of the air flow.

Abstract Image

可视化光学通用电机气隙中的两相流及其对扭矩的影响
电动交通的实现需要高功率密度的电机。为此,人们越来越多地考虑采用直接液体冷却方法,即将油注入电机舱。这样就形成了可用于高效冷却的两相流。不过,油也会渗入转子和定子之间的气隙,也会因摩擦增加而导致额外的损耗。由于人们对此类系统中的两相流动,尤其是气隙中的两相流动知之甚少,因此我们通过简单的光学可视化、高速激光诱导荧光成像以及扭矩测量等方法对其进行了研究。测量是在直接冷却电动机的光学可视通用模型的气隙中进行的。转速变化范围为 100 至 2000 rpm,观察到三种不同的两相流动状态。低速时(流态 1),气隙局部径向充满油,中速时(流态 2)充满泡沫,而高速时(流态 3)转子和定子上出现分离的薄膜。两相运行和单相运行之间的扭矩差(量化注入油造成的机械损失)由于气隙中的油而持续增加,直到在流态 2 中由于形成泡沫而达到最大值。在流态 3 中,扭矩差为负值。这是因为定子的凹槽中充满了油,从而减少了气流产生的湍流。
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来源期刊
Experiments in Fluids
Experiments in Fluids 工程技术-工程:机械
CiteScore
5.10
自引率
12.50%
发文量
157
审稿时长
3.8 months
期刊介绍: Experiments in Fluids examines the advancement, extension, and improvement of new techniques of flow measurement. The journal also publishes contributions that employ existing experimental techniques to gain an understanding of the underlying flow physics in the areas of turbulence, aerodynamics, hydrodynamics, convective heat transfer, combustion, turbomachinery, multi-phase flows, and chemical, biological and geological flows. In addition, readers will find papers that report on investigations combining experimental and analytical/numerical approaches.
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