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Numerical Study of a Linear Cascade With Upstream Cavity Using Various Rim-Seal Geometries and Purge Rates

This paper introduces numerical investigation of a low-speed linear cascade rig with upstream cavity at Reynolds number commonly observed in modern low-pressure turbine stage. This configuration was tested experimentally during the EU project MAGPI (2007–2011) focused on the impact of secondary air systems on gas turbine performance. Three different purge mass flow rate have been tested numerically using three different rim-seal geometry (axial clearance, simple and double radial overlap). The mechanisms and influence of these two parameters on loss generation for the main annulus flow is investigated. The ability of high-fidelity numerical methods to deal with such kind of configuration is assessed by comparing several unsteady codes over the axial geometry at three purge mass flow rate available. Two Large-Eddy Simulation (LES) solvers based respectively on structured and unstructured meshes and a LES-LBM approach in which equations discretization is based upon a Lattice-Boltzmann Method (LBM) and a Sub-Grid Scale (SGS) model from LES developments are used. The comparison against MAGPI experiments and previous Reynolds Averaged Navier-Stokes (RANS) simulation show that despite a variety of flow dynamics modelling, discretization and numerical parameters, the different unsteady codes are well able to recover aerodynamic quantities into the mainstream passage in which purge flow blows at various rate and different rim-seal geometry. Further results obtained from such high-fidelity methods exhibit strong interaction of separated hub boundary at rim-seal interface with nonuniform pressure field imposed by downstream blade leading to a strong in-depth of mainstream flow into the cavity for the axial clearance. Simple and double overlap damper this phenomenon due to localized recirculation zone into the rim-seal. In addition, hub passage vortex and blade suction side unsteadiness are shown to be strongly related to the vortex shedding process occurring at rim-seal interface.