# Comprehensive Investigations on Fluid Flow and Cavitation Characteristics in Rotating Disk System
## 1 Introduction  
In wet clutch, hydro-viscous clutch, and other transmission components and mechanical seals, the complex force interaction between oil and disk structures directly affects the transmission efficiency of the vehicle transmission system and the reliability of the seal. Firstly, [PERSON] [1] studied the flow on rotating disk in 1921, and discussed the rotating flow of a stationary fluid on the surface of an infinitely large rotating disk, i.e., the \"free disk\" problem, which is actually a common fluid flow problem in rotating equipment such as compressors and centrifugal pumps. Based on the assumption of axisymmetry and similar transformations, he first transformed the control equations for constant incompressible axisymmetric flow in cylindrical coordinates into a set of nonlinear differential equations and found that the angular velocity of the fluid decreases gradually from the rotational velocity of the disk to zero as the axial distance from the disk increases. The fluid boundary layer attached to the disk surface was called the \"[PERSON] boundary layer\" or \"Ekman layer\". [PERSON] [2] used numerical integration to solve the system of equations proposedby [PERSON] to obtain the axial and radial velocity distributions of the fluid in the \"free disk\" problem. [PERSON] [2] used numerical integration to solve the system of equations proposed by [PERSON] to obtain the axial and radial velocity distributions of the fluid in the \"free disk\" problem. Based on [PERSON]'s analysis, [PERSON] [3] studied the flow formed by rotating an infinitely large stationary disk with constant angular velocity. In this case, the angular velocity of fluid gradually decreases from the constant angular velocity to zero as it approaches the disk surface, and the boundary layer adhering to the disk surface is called the \"Bodewadt boundary layer\". With the development of fluid drive and control technology, people have a new understanding of disk flow [4; 5; 6]. [PERSON] [7] analyzed whether the rotating disk boundary layer can still guarantee absolute stability when disk system spacing is sufficiently small, and the results showed convective instability when radial flow is also present. [PERSON] [8] studied the flow behavior of magnetic fluids in rotating interfaces and found that the velocity near the passive sheet decreased when the viscosity increased, and fluid temperature as well as the concentration and Reynolds number were inversely proportional. [PERSON] [9] et al. used four dimensionless cases to analyze the strongly rotating flow and the stability in the turbine disk cavity and found that the parameters such as flow Reynolds number, rotational Mach number, and rotational Reynolds number affect the stability of the disk cavity system greatly. Surface micro-texture technology refers to the introduction of structures, such as micro-dimples, micro-grooves, micro-convex bodies, etc., to improve the frictional lubrication properties of the sliding mechanical interface [10; 11; 12; 13; 14]. [PERSON] [15] et al. were the pioneers to analyze the effect of micromorphology between parallel plates on the dynamic pressure bearing capacity through the dimensionless and similarity principle of equation, and the effect of factors such as depth, arrangement distribution and relative area of the micromorphology. [PERSON] and [PERSON] [16] researched the effect of different texture dimples on hydrodynamic lubrication and friction performance and found that it affected the frictional coefficient lightly, and triangular texture can significantly increase load carrying capacity reducing leakage of oil. [PERSON] [17; 18] et al. analyzed the effect of texture shape and texture orientation on hydrodynamic pressure by a super-relaxation iterative algorithm and used average dimensionless pressure as an index to assess bearing capacity, and found that elliptical dimples perpendicular to the sliding direction produced the best lubrication performance. [PERSON] [19] et al.