Abstract
Flow within the space between the rotor and stator of a turbine disk, and an area referred to as the rim seal cavity, develops azimuthal velocity component from the rotor disk. The fluid within develops unsteady structures that move at a fraction of the rotor speed. A test is designed to measure the number of unsteady structures and the rotational speed at which they are moving in the rim seal cavity of an experimental research rig. Data manipulation was developed to extract the speed, and the numbers of structures present using two fast-response aerodynamic probes measuring static pressure on the surface of the nozzle guide vane (NGV)-side rim seal cavity. A computational study is done to compare measured results to a transient unsteady Reynolds-averaged Navier–Stokes (URANS). The computational simulation consists of eight vanes and ten blades, carefully picked to reduce the error caused by blade vane pitch mismatch and to allow for the structures to develop correctly, and the rim seal cavity to measure the speed and number of the structures. The experimental results found 15 structures moving at 77.5% of the rotor speed, and the computational study suggested 14.5 structures are moving at 81.7% rotor speed. The agreement represents the first known test of its kind in a large-scale turbine test rig and the first known “good” agreement between computational and experimental work.
Highlights
Design of a turbine stage requires a gap between the non-moving stator wall and the rotating blade disk below the hub endwall surface
The rotor speed is a corrected value based on the current atmospheric temperature
Purge mass flow injection rate is defined as the mass rate of the fluid being injected into the rim seal cavity externally
Summary
Design of a turbine stage requires a gap between the non-moving stator wall and the rotating blade disk below the hub endwall surface. Air within the rim seal cavity begins to swirl due to momentum imparted on the fluid through boundary layer interaction with the rotor disk. Turbine flow interactions near rim seals are highly influential in turbomachinery design, affecting the aerothermal performance of the stage. Additional cooling air to prevent ingestion of the hot main annulus gas into the turbine disc cavity are required. As the system of swirl develops, a system of high- to low-pressure cells moves within the rim seal cavity. A good understanding of the unsteady structures in the rim seal cavity are essential in improving the aero-thermal performance characteristics of an axial flow turbine
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