Angel wing overlap length effect on rim seal design

Abstract

Gas turbine engines are a type of energy conversion machines that have civil and military applications and used in many fields such as aircrafts, sea vehicles and electricity generation. They are subdivided as turbojet, turbofan, turboprop and turboshaft according to their usage areas. Three main components compose the main flow path of the gas turbine engines. These are compressor, combustion chamber and turbine. The main flow path consists of stationary and rotating parts. The openings between rotating and stationary parts cause parasitic flows. For this reason, the engine's secondary air system (SAS) is designed to pressurize the rotor-stator cavities, to ensure the sealing between rotating and stationary parts, and cool down the parts that are exposed to high temperatures. To pressurize rotor-stator cavities, rim seal design and flow calculations play an important role in gas turbine engine design. While pressurizing the rotor-stator cavity, the SAS flow also cools down the cavity, and hence improves the rotating and stationary part's life and durability limits. In order to do that, preventing hot gas ingestion into the cavity completely or partially holds an important role. The amount of cooling air used in the cavity highly depends on the boundary conditions and geometry of the rim seal. The use of a large amount of cooling air contributes positively to component strength and life, while reducing overall engine efficiency and increasing specific fuel consumption. Meanwhile, designing complex rim seal geometry reduces the cavity cooling air requirement but makes the manufacturing processes difficult and clearance control challenging at the rim seal. As a result, the pressurization of the rotor-stator cavity with the appropriate flow rate makes the rim seal design vital. The aim of this master thesis is to examine the amount of ingestion from the main flow into the cavity in terms of overlap distance and clearance of the angel wing. In this way, it is aimed to make more precise predictions while designing the rim seal and calculating sufficient amount of cooling air. In this thesis, a validation study was performed using an experimental data from the literature. A methodology was applied by selecting proper geometry and methods for CFD solutions. Grid independency study was also carried out for the CFD model. Based on literature data, a parametric study was exerted by looking at the effects of the amount of overlap length at a radial opening for a rim seal configuration. The results were evaluated and visualized.