Large-Eddy Simulation of the Unsteady Full 3D Rim Seal Flow in a One-Stage Axial-Flow Turbine

Abstract

The flow field in a complete one-stage axial-flow turbine with 30 stator and 62 rotor blades is investigated by large-eddy simulation (LES). To solve the compressible Navier-Stokes equations, a massively parallelized finite-volume flow solver based on an efficient Cartesian cut-cell/level-set approach, which ensures a strict conservation of mass, momentum and energy, is used. This numerical method contains two adaptive Cartesian meshes, one mesh to track the embedded surface boundaries and a second mesh to resolve the fluid domain and to solve the conservation equations. The overall approach allows large scale simulations of turbomachinery applications with multiple relatively moving boundaries in a single frame of reference. The relative motion of the geometries is described by a kinematic motion level-set interface method. The focus of the numerical analysis is on the flow inside the rim seal between the stator and the rotor disks. Full $360^{\circ }$ computations of the turbine stage are performed for two rim seal configurations. First, the impact of the mesh resolution on the LES results is analyzed for the single lip rim seal configuration. Second, the LES results are compared to experimental data, followed by a detailed analysis of the unsteady flow field. For the single lip rim seal configuration, two modes unrelated to the rotor frequency and its harmonics are identified inside the rotor-stator wheel space, where the first more dominant mode shows a major impact on the ingress of the hot gas into the rotor-stator wheel space. The second mode is a counter-rotating mode which results from the interaction of the first mode with the flow field downstream of the stator blades. Third, at the same operating condition a modified configuration with a double lip rim seal is investigated and compared to the reference configuration to demonstrate the impact of the rim seal geometry on the overall flow field. The additional lip on the rotor disk damps the aforementioned modes and reduces the ingress of the hot gas resulting in an increase of the cooling effectiveness inside the rotor-stator wheel space, which is in a good agreement with the experimental results.