# Structural Design and Optimization of Herringbone Grooved Journal Bearings Considering Turbulent
## 1 Introduction  
Computed tomography is a combination of the rapid development of computer technology and X-ray technology in modern times [1]. The CT machine using this technology is an indispensable device for modern clinical diagnosis, and it plays an increasingly important role in the medical field. The CT ball tube is the core component of the CT equipment, and it is expensive. On the one hand, the performance of the CT ball tube must meet the requirements of high speed, high definition of CT imaging, high power, and high reliability. On the other hand, it is hoped that it has a longer life and lower cost [2]. The continuous popularization of CT machines has brought a huge market demand for CT ball tubes, so the development of CT ball tubes with superior performance is of great significance and market value. The anode target located in the CT tube spirally moves around the patient to obtain a three-dimensional image of the patient. In recent years, in order to shorten the diagnosis time and improve the image resolution, the anode target speed has become higher and higher, and the centrifugal force on the CT tube has also greatly increased, which has made the previous rolling bearings that used solid lubricants to load no longer applicable [3]. Compared with rolling bearings, journal bearings run more smoothly and can better meet the requirements of supporting anode targets. The CT tube is small in size and requires high sealing performance, so an external oil supply system cannot be used. Because the structureof the herringbone groove bearing is relatively compact, it can realize self-lubrication, self-sealing, good stability, low temperature rise, long working life, and other characteristics; and become a good choice for CT ball tube bearings [4; 5; 6]. When the rotation speed of the bearing increases, the temperature of the lubricating medium will increase significantly, and the viscosity will decrease, and the bearing capacity will decrease, which is prone to accidents [7; 8]. Due to the high-temperature and high-vacuum working environment in the CT tube, the bearing lubricating medium supporting the high-speed rotation of the anode target needs to meet the requirements of high temperature resistance, high thermal conductivity and low vapor pressure. Due to a large amount of research on liquid metals in recent years, it is possible to find a lubricant that satisfies such conditions. Among them, the performance of gallium-based liquid metals is the most prominent. Gallium-based liquid metal has relatively low viscosity, high thermal conductivity, certain inertness, nontoxicity, and good stability [9]. At the same time, the vapor pressure of gallium metal is particularly low compared to other liquid metals, and it still remains liquid in a high vacuum state, so it can be used in a high vacuum environment. Many of the latest CT equipment use gallium-based liquid metal for lubrication, such as the IMRC tube produced by Philips, which abandons the traditional ball or roller bearing structure and adopts a new spiral groove bearing. The unique liquid metal lubricant has greatly improved the heat dissipation rate. The research on herringbone grooved journal bearings mainly focuses on the optimization of the performance of the herringbone grooves and their structural parameters [10; 11; 12]. [PERSON] et al. used herringbone grooves to improve bearing performance [13; 14; 15]. [PERSON] [16] analyzed the bearing performance of three distribution forms of herringbone grooves. The results show that herringbone grooved journal bearings have good and predictable stability characteristics and can run stably at the center and near-center positions. At the same time, experiments were carried out to verify the correctness of the theoretical results. [PERSON] et al. [17] conducted a related study on the performance characteristics of herringbone grooved journal bearings with an arc-shaped bottom surface based on the finite difference method and found that the oil film load capacity is worse than that of a smooth journal bearing.