Christopher Fuhrer

Numerical Investigation on Spontaneous Condensation in Low-Pressure Steam Turbine Aeroelasticity


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ISBN:

978-3-8440-8099-5

Series:

Strömungstechnik

Keywords:

steam turbine; flutter; aerodynamic damping; cfd; condensation; aeromechanics; flutter prediction; low-pressure turbine; last stage

Type of publication:

Thesis

Language:

English

Pages:

176 pages

Figures:

88 figures

Weight:

260 g

Format:

21 x 14,8 cm

Bindung:

Paperback

Price:

48,80 € / 61,10 SFr

Published:

July 2021

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Abstract:

In steam turbines, condensation of water vapor, which usually occurs in the last stages, leads to the formation of droplets. This changes the course of the expansion and the thermodynamics of the flow. Additionally, last stage rotor blades feature a long and slim blade design and are thus prone to flutter. The aim of this study is to numerically investigate the influence of wet steam effects on the flutter behavior of turbine blades.

Extensively validated numerical models are used to describe the two-phase flow, including droplet formation and growth under thermodynamic non-equilibrium conditions. To predict the aerodynamic damping, the energy method with influence coefficients is used as a today's state of the art approach.

Different wetness conditions are defined at the inlet of a tip section of a rotor blade. At first, different droplet sizes and wetness contents. Then, dry inlet conditions with strong spontaneous condensation occurring at different positions in the blade passage. Two mechanism that change the flutter behavior could be identified, a change of the shock structure and the speed of sound due to nucleation and droplet growth. Generally, the torsion mode is more susceptible to wet steam influence than bending modes. Finally, the results of modeling with the sophisticated wet steam model are compared to simple single-phase approaches.