## 1 Introduction  
Double-row tapered roller bearings (TBR) can withstand large radial and axial loads. These attributes have facilitated their wide application in helicopter transmission systems and other important fields. However, during the bearing operation process, failures may occur owing to excessive load and poor lubricating oil quality, which could lead to severe safety accidents. The distribution of lubricating oil flow fields in the bearing cavity of double-row TBRs is directly related to their service life. Therefore, it is necessary to conduct an in-depth study on their distribution in the cavity of double-row TBRs. The law of movement of oil and gas two-phase flow is relatively complicated. At present, advanced experimental methods are generally used to obtain the law of two-phase flow. [PERSON] et al. [1] used PIV technology to measure the flow field distribution in the bearing and found that there are exit eddy currents on both sides of the steel ball; as the bearing speed increases, the vortex size increases. [PERSON] et al. [2, 3, 4] used a high-speed camera to study the distribution of oil inside the bearing under oil injection lubrication. The study found that most of the oil was distributed near the outer ring; the oil volume fraction inside the bearing increased with the increase in inlet flow. [PERSON] [5] also uses a high-speed camera to study the flow field distribution of the ball bearing under oil injection lubrication. With the advancement of computer technology, the computational fluid dynamics (CFD) method has been widely adopted in the analysis and research of flow fields in rotating machinery [6], like bearings and gears. [PERSON] et al. [7] simulated the movement of a needle roller bearing using the moving reference frame method. By comparing the distributions of the oil volume fractions at two different inlet positions for lubricating oil, they obtained the best position for setting the lubricating oil inlet. [PERSON] et al. [8] used the volume of fluid (VOF) multiphase flow modeling method and the mesh adaptive technology to track the two phases of oil and gas in the bearing cavity of a certain engine and obtained the distribution law of the lubricating oil in the bearing cavity. [PERSON] et al. [9] employed the turbulence model and the VOF method to study the gas-liquid flow characteristics in the bearing fluid domain. They obtained the distributions of the flow, pressure, and velocity fields of the lubricating oil in the bearing cavity under the uniform gas-liquid two-phase condition. [PERSON] et al. [10] established a 3D transient simulation model of the oil-gas two-phase flow in high-speed angular contact ball bearings based on the VOF method and sliding mesh technique. They studied the characteristics of the flow field in the bearing cavity and obtained the distribution law of lubricating oil--such that the average volume fraction of the lubricating oil decreases with the increase of rotational speed but increases with the increase of oil flow. [PERSON] et al. [11] used the rotating reference frame method and the VOF model to analyze the gas flow of roller bearings under different rotational speeds and cage structure parameters. They determined the influence laws of the bearing revolution, steel ball spin, cage structure, and other parameters on the bearing lubrication performance. With the angular contact ball bearing as the research object, [PERSON] et al. [12] analyzed the influence of the lubrication and working condition parameters on the oil and gas two-phase flow field in the bearing. Their study showed that the lubricating oil is mainly distributed on the surface of the inner and outer ring raceways and the ball surface of the bearing, and is slightly distributed near the cage. [PERSON] et al. [13] tracked the oil and gas two-phase flow in the roller bearing under ring lubrication using the CLSVOF multiphase flow analysis method and analyzed the influence of factors, such as the rotational speed on the distribution of the lubricating oil.