A COMBINED NUMERICAL AND EXPERIMENTAL INVESTIGATION OF CHARACTERISTICS IN A ROTOR-STATOR CAVITY WITH RADIAL INFLOW

The present paper is devoted to the numerical and experimental investigation of flow characteristics and pressure distribution in a rotor-stator cavity of different aspect ratio with various radial inflow. The numerical simulations are carried out with axisymmetric and 3-D sector models, whose aspect ratio G varies between 0.01 and 0.2, for various β0 (0~0.8), λT (0.022~0.287). The results show that the flow under most of these conditions belongs to the Batchelor type family. However, for conditions with small G and high λT, the radial velocity is no longer negligible and results in more pressure losses because of hydraulic frictional resistance. For the conditions with big aspect ratio and small λT, whose radial Rossby number is much smaller than 1, the N-S equation for tangential component of the flow in the rotating core reduces to the balance of the centrifugal force and the radial pressure gradient, therefore the radial distribution of pressure is decided by the central core swirl ratio β. Furthermore, the numerical investigation shows that the radial distribution of β can be correlated, in the case of small aspect ratio, according to a 5/7 power-law. On the other hand, in the case of big aspect ratio the radial distribution of β can be correlated according to a modified 5/7 power-law. The experiments acquire the tangential velocity and static pressure distributions of the conditions whose aspect ratio equals 0.2 by pressure transducers and three-hole probe. The measurement data verify some conclusions of the numerical investigation. INTRODUCTION In medium and small aeroengines which have the structure with high pressure ratio centrifugal compressor, the air used to realize the functions of secondary air system such as cooling of turbine blades and disks, sealing of turbine cavities and bearing chambers, adjusting of rotating assembly axial load, is commonly bled off from the main flow at the root of the centrifugal impeller and drawn radially inwards through the impeller rear cavity. Due to the variations of geometry and flow parameters of the impeller rear cavities, the characteristics of pressure loss and pressure distribution follow complex variation law. Therefore, the thorough understanding of the flow mechanism in a rotor-stator cavity with radial inflow, represented by the impeller rear cavity, is the key to design the rational secondary air system. The researches of the flow in a rotor-stator cavity with radial inflow are based on the studies of the flow in the cavity with infinite disks. Batchelor (Batchelor, 1951) solved the system of differential equations relative to the stationary axisymmetric flow between two disks of infinite radius. He specified the formation of a nonviscous core in the solid body rotation, confined between the two boundary layers that develop on the disks. The boundary layer on the stationary disk is called the Bödewadt layer and flows radially inward, the boundary layer on the rotating disk is called the Von Kármán or Ekman Layer and flows radially outward. However, this result has been contrasted by Stewartson