## 1 Introduction  
Water-lubricated thrust bearings (WTBs) are the key support components of reactor coolant main pumps [1] and new marine thrusters [2]. The propeller thrust of a ship's rim-driven thrusters (RDTs) is borne by the WTBs. As a result of the low viscosity of water, the load-carrying capacity of water-lubricated bearings is weaker than that of oil-lubricated bearings under the same working conditions, leading to lubrication failure and abnormal wear [3]. Moreover, the WTBs of the reactor coolant main pump and high-power RDT (more than 3 MW) operate at a large linear velocity (70-90 m/s), heavy load (\(\geq\)0.5 MPa), and low viscosity, resulting in a quite different Reynolds number distribution of the pads. In this case, the pad surface is not a single pattern of laminar or turbulent flow but rather a mixed flow pattern. Complex flow characteristics make it difficult to establish the lubrication model and affect the accuracy of bearing performance prediction. Experiments are important means by which to explore flow patterns and their transformation phenomena. [PERSON] et al. [4] found that parameters such as the bearing power loss and increase in temperature affect the increase in speed in the bearing test of steam turbine units and speculated that this phenomenon may be related to the transition of the flow pattern. [PERSON] et al. [5] observed the generation and development of laminar flow instability and the Taylor vortex in a sliding bearing through a dyeing test and obtained pictures of the flow pattern transition process. [PERSON] et al. [6] observed the flow pattern transition process of an oil-lubricated journal bearing using the bubble tracing method and photographed the coexistence of laminar and turbulent flow. These tests provide direct proof of the existence of a mixed flow pattern. Bearing mixed flow pattern modeling is also a research hotspot, as some scholars have tried to use the three-dimensional N-S equation to explain the relationship of laminar flow to turbulent flow, but the calculation's accuracy remains to be verified. Improvement of the turbulence model is a feasible method for a mixed flow. The Constantscu model [7], Ng-Pan model [8], and Elrod-Ng model [9] are the most popular turbulence models presently. [PERSON] et al. [10] studied the influence of journal inclination on the static and dynamic characteristics of journal bearings reinforced by low dynamic visibility fluid in laminar and turbulent flow, respectively. [PERSON] et al. [11] proposed a new model of Reynolds stresses for transition-turbulent theory and used it to analyze the sector-shaped thrust bearing in the transition region. [PERSON] et al. [12] studied the effect of turbulence on the thermo-hydrodynamic performance of tilting pad journal bearings and found that the effect of the non-laminar flow on the predicted performance was not negligible at high rotational speeds. [PERSON] et al. [13] established a database of turbulent lubrication parameters. Their simulation results obtained for the bearing performance were closer to the test results than the common turbulence model, but the coexistence of laminar and turbulent flows was not considered. [PERSON] et al. [14] presented turbulence models for combined Couette-Poiseuille flows, and the effects of the inertia forces on the laminar and turbulent flows were discussed. [PERSON] et al. [15] researched the effect of turbulence and misalignment on the steady state characteristics of a centrally loaded single-pad externally adjustable bearing using the Ng-Pan model. [PERSON] et al. [16] investigated the turbulent flow pattern and the elastic effect in a journal bearing subjected to high speeds using ANSYS CFX. [PERSON] et al. [17] thought that turbulence may locally develop in a large bearing and found that turbulence decreased the speed of the transition from a mixed-lubrication regime to a hydrodynamic lubrication regime. In summary, the theory of full laminar and turbulent flows is relatively mature.