Experimental Investigation of Mass Flow Exchange Ratio and Core Swirl Ratio in a Novel Dual-Cavity Test Rig With Heated Rotating Compressor Cavities

Abstract The blade tip clearance within an aero-engine high pressure (HP) compressor is an important factor influencing the efficiency of the engine. Consequently, it is a crucial parameter in the design of next-generation engines. The transient clearance of the blades depends directly on the radial expansion of the rotating compressor disks. In the shroud area, these disks are heated by the hot main gas flow, where the flow of the secondary air system cools these disks in the cob area. At high rotational speeds, buoyancy forces dominate the flow within the cavities. They create a three-dimensional flow field that interacts with the compressor disks. Thus, it is necessary to have a deep knowledge of the heat transfer and flow structure in buoyancy-dominated rotating cavities with modern disk geometries. Therefore, a novel dual-cavity test rig for experimental investigation in rotating cavities is described within this paper. The rig consists of three rotor disks, that form two symmetrical cavity sections. These cavities are limited by an inner shaft, which is designed to be either stationary or rotating. The modular design of the test bed allows investigations for different values of geometric parameters, such as cavity gap width or inner shaft ratio. In order to investigate operating points (OP) with a thermal gradient and to set the rig conditions close to those of modern jet engines, the shroud is heated by a heating module. To determine the mass flow exchange ratio of the first cavity, fluid temperatures are measured in the middle of the axial bore flow and on both sides of the cavity, within 10 mm distance from the disk surface. To calculate the core swirl ratio of the rotating core, the static air pressure is measured at various radial positions in the first cavity as well as the radial distribution of the disk surface temperature. Inlet and outlet conditions of the fluid passing the cavity were measured by the internal telemetry system. Finally, this paper presents time-averaged measurement data of the core swirl ratio β and the mass flow exchange ratio M within the variation of various non-dimensional parameter in the range of 4.2 · 103 ≤ Rez ≤ 1.2 · 105, 4.6 · 105 ≤ Reϕ ≤ 1.0 · 107 and 9.0 · 10−2 ≤ βTΔT ≤ 3.5 · 10−1.