# Effect of Rotational Speed Variation on the Flow Characteristics in the Rotor-Stator System Cavity
## 1 Introduction
[15] simplified the high-pressure part of the gas turbine model, conducted a rotor-stator system test, and obtained the influence of the heat generated by the windage on the surface temperature change in the cavity. [PERSON] et al. [16] divided the flow into Batchelor and Stewartson structures according to whether there is a rotating vortex core in the axial inlet cavity. [PERSON] et al. [17] proposed that, in a certain range of rotational Reynolds numbers, the streamline curvature instability plays a leading role in the transition process from the rotor boundary layer to turbulence. Clearance flow is more widely available in practical applications and many scholars have worked on various aspects of clearance flow. [PERSON] et al. [18] employed numerical and experimental studies to assess the variables influencing the energy efficiency of a new regenerative evaporative cooler utilizing indirect evaporative cooling at the dew point. Internal heat transfer and efficiency are investigated in the experiments by varying the size of the clearance. [PERSON] et al. [19] addressed the problem of leakage and pressure distribution in centrifugal pumps and proposed a theoretical model for the direct prediction of leakage flow. He developed a pressure model for the simplified geometry of an open rotor-stator cavity by introducing [PERSON]'s \(K\) formula. Predictions from the new one-dimensional pressure model showed good accuracy and outperformed those from a pressure model using the conventional constant \(K\), when compared with the measured casing wall pressure of an adjustable-speed centrifugal pump. [PERSON] et al. [20] quantitatively analyzed the underwater model using a numerical approach with a boundary element method-finite element method model. Based on the proposed model, a code has been developed which can be applied to any two- and three- dimensional water tank with an arbitrarily shaped elastic underwater structure. [PERSON] et al. [21] proposed a rigid vortex transport equation based on vorticity decomposition, which can be used to distinguish rigid rotation from shear motion of a local fluid. This equation provides a practical method for the analysis and control of interstitial vortex flow. [PERSON] et al. [22] performed numerical simulations of three-dimensional compressible flow in a water poppet valve model and analyzed three types of cavitation at different locations within the valve based on vortex dynamics. It was calculated that the vortex cavitation within the free shear layer is due to vortex dynamics,while the additional cavitation at the trailing edge of the poppet valve and in the chamfered recess is caused by flow separation. Based on the analysis of the flow characteristics in the rotor-stator system cavity, some researchers have studied the influence of the rotating speed on the flow field distribution and rotor torque. [PERSON] et al. [23] adopted the large eddy simulation method to numerically study an enclosed annular rotating static system. As the speed is incremented from 2000 rpm to 10,000 rpm, the flow structure varies from a torsional Couette type to a Batchelor type. In addition, the turbulence near the rotor side and near the stator side is highly anisotropic, as obtained by Reynolds stress analysis. By simplifying the clearance flow in fluid machinery into the cavity flow of a classical cylindrical inlet rotor-stator system, the internal flow was analyzed quantitatively by means of dimensionless parameters, and the variation law of disc torque at different rotating speeds was studied. Previous scholars tended to ignore the variation in swirling vortex within the cavity in their studies of the rotor-stator system. By monitoring different variables within the cavity, a correlation was found between the change in shear strain rate and the separation of the swirling vortex as the rotation speed increased.