Loss Assessment of the Axial-Gap Size Effect in a Low-Pressure Turbine

Abstract

The aim of this work is the decomposition, quantification, and analysis of losses related to the axial gap size effect. Both experimental data and unsteady RANS calculations are investigated for axial gaps equal to 20 %, 50 % and 80 % of the stator axial chord. A framework for identifying sources of loss typical in turbomachinery is derived and utilized for the low-pressure turbine presented. The analysis focuses on the dependency of these losses on the axial-gap variation. It is found that two-dimensional profile losses increase for smaller gaps due to higher wake-mixing losses and unsteady wake-blade interaction. Losses in the end-wall regions, however, decrease for smaller gaps. The total system efficiency can be described by a superposition of individual loss contributions, the optimum of which is found for the smallest gap investigated. It is concluded that these loss contributions are characteristic for the medium aspect-ratio airfoils and operating conditions investigated. This establishes a deeper physical understanding for future investigations into the axial-gap size effect and its interdependency with other design parameters.

Effect of Diffuser Inhomogeneity on Full-Annulus Axial Turbine Performance

“…The isolated turbine configuration has been the subject of several studies, e.g., Henke et al (2016) and Oettinger et al (2019b), where both the geometrical parameters and aerodynamic characteristics are described in detail, of which a summary is given in Tab. 1.…”

“…The TRACE solver (Franke et al, 2005), which is being developed by the German Aerospace Center (DLR) in cooperation with MTU Aero Engines AG, is used for steady-state calculations. For the turbine section, details regarding the numerical setup and grid can be found in Oettinger et al (2019b). Turbine and diffuser consist of structured meshes, the exit casing is described by an unstructured mesh with 34,393,070 grid cells due to its more complex geometry.…”