Design Considerations and CFD for a Novel Rotor-Stator Cavity Test Rig

This paper presents the design and setup of a newly designed test rig for the investigation of flow and heat transfer phenomena in rotor-stator cavities. To focus purely on this complex interaction, the rotating cavity is setup without any channel mimicking a hot gas path. Rotating and stationary temperature measurements as well as PIV measurements will be conducted simultaneously to quantify the fluid-structure and heat transfer in a rotor-stator cavity, whose design is inspired by modern turbine designs of aircraft engines. The rotor consists of three parts, fitted together by a combination of interference fits and high-strength bolted connections. Results of FEM computations of the design of this rotor are presented. Regions of high stresses due to rotation and temperature loads are pointed out and operating limits are defined. Furthermore, the rolling bearing system is presented and the resulting rotordynamic behaviour is analysed. Radial and axial stiffness of the roller bearings themselves, as well as those of the housing and foundation are considered. Finally, results of preliminary fluid dynamic simulations are presented in order to underline the advantages of this test rig and the phenomena, which are expected in the experimental investigations. INTRODUCTION Flow phenomena and heat transfer mechanisms inside rotor-stator cavities and fully enclosed rotor cavities have been the main focus of many works in the past. Both fields of research and their applicability are vast and especially the latter can in general not be investigated, without considering at least general results of the first. Due to its nature, most components of turbomachines are exposed to multiple phenomena in rotor-stator and fully enclosed rotor cavity problems and specific research in this field is of special interest. Typical flow phenomena in such cavities have been known for a long time, since the well-known publications of (Batchelor, 1951) and (Stewartson, 1953), who both analytically investigated the flow over and inside rotating, infinitely large discs and presented analytical solutions to the reduced, axisymmetric Navier-Stokes-Equations. During the time of these publications, some controversies existed. On the one hand, Batchelor’s solution describes a solid, nonviscous body of fluid, confined between the boundary layers at the enclosing rotating disks, which is rotating at some speed, slower than the disks themselves. On the other hand Stewartson found a solution, in which the tangential velocity of the fluid is zero everywhere, except in the boundary layer at the disks. Since then, many numerical and experimental investigation regarding flow phenomena inside such cavities have been published. (Itoh et al., 1992) performed early experiments of the flow inside an enclosed rotor-stator system. Velocity and Reynolds-Stress components where measured using traversable hot-wire probes. A large overview of early works on rotorstator systems is given in (Owen and Rogers, 1992). (Poncet et al., 2005) and (Da Soghe et al., 2012) both numerically and experimentally investigated the flow inside a rotor-stator cavity with different aspect ratios, rotational Reynolds numbers and with and without varying centripetal and centrifugal through-flow rates. The radial dimensions of their test rig was in the same order of magnitude as the newly designed rig. Axial dimensions in the new rig are three to six times larger. Extensive LDA measurements as well as static pressure measurements on the stationary wall have been performed, in order to characterize the flow inside the cavity. Their numerical simulations have been carried out on a sector model of the experimental domain with five elements in circumferential direction. The ratio of the radial cell height Δr to the height of