Einfluss von Kühlluft auf die Aerodynamik und Aeroelastik einer fünfstufigen Axialturbine

authored by

Lennart Stania

supervised by

Jörg Reinhart Seume

Abstract

The conversion of thermal energy into electrical energy while minimising greenhouse gases is one of the key problems in the contemporary era. The conversion is primarily realised within turbomachinery, where enhancing efficiency or transitioning to renewable fuels reduces carbon dioxide emissions. This requires precise design methods that accurately predict aerodynamic loads on turbine blades. Only with accurate load predictions can the structures be further optimized aerodynamically with sufficient safety margins against machine failure. Thermal disturbances in the form of injected cooling air can represent an excitation mechanism, however this effect has not been investigated for high excitation orders in the past. Hence, this thesis describes an experimental setup that injects cooling air in the fourth vane stage of a five-stage axial turbine. The aerodynamic and aeroelastic behaviour is evaluated base on injected cooling air. The experimental investigations and the numerical modelling of the test rig shows a significant influence of the cooling air on the total temperature in the axial turbine. The Mach number and total pressure distributions are unaffected by isokinetic cooling air injection, which can be explained by the unchanged momentum of the flow. These changes result in oscillations in the angle of attack of the blade, serving as an excitation mechanism that can amplify blade vibrations. A maximum increase of 20% in vibration amplitude of the fifth blade is measured in the experiment. A doubling of vibration amplitude was observed for individual blades. The stimulating force is largely dependent on the mixing of the cooling air, which depends, among other things, on the cooling air mass flow, the temperature difference between the cooling air and the main flow, and the through-flow rate. The results of this work show that a correct representation of the cooling air is necessary in the design process of turbomachinery in order to successfully predict the aerodynamic behaviour and the fatigue strength of the rotor series. The numerics are able to correctly predict the tendencies of the experiment, so that the numerics are suitable for the design of cooling air effects.

Organisation(s)

Institute of Turbomachinery and Fluid Dynamics

Type

Doctoral thesis

No. of pages

159

Publication date

2024

Publication status

Published

Sustainable Development Goals

SDG 7 - Affordable and Clean Energy

Electronic version(s)

https://doi.org/10.15488/18003 (Access: Open)