An investigation of CFD simulation for estimation of turbine RUL

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dc.contributor.advisor Heyns, P.S. (Philippus Stephanus)
dc.contributor.coadvisor Dunn, Dwain
dc.contributor.postgraduate Maré, Charl Francois
dc.date.accessioned 2019-05-16T15:58:25Z
dc.date.available 2019-05-16T15:58:25Z
dc.date.created 2019-04-25
dc.date.issued 2018
dc.description Dissertation (MEng)--University of Pretoria, 2018. en_ZA
dc.description.abstract Turbines encounter blade failures due to fatigue and creep. It has been shown in the literature that the primary cause of steam turbine blade failures worldwide can be ascribed to fatigue in low pressure (LP) turbine blades. The failure and damage to these blades can lead to catastrophic consequences. Some utilities use empirical methods to determine the forces experienced by turbine blades but desire more accurate methods. The inaccurate prediction of high-cycle fatigue (HCF), thermal durability and stage performance is introduced when one does not consider blade row interaction. Blade row interactions can, however, be accounted for by means of computational fluid dynamics (CFD). Furthermore, modern high- fidelity CFD tools would be able to contribute greatly in predicting the forces experienced by turbine blades. Numerical tools such as CFD and nite element analysis (FEA) can greatly contribute to the estimation of the remaining useful life (RUL) of turbine blades. However, in this estimation process, there are various uncertainties and aspects that affect the estimated RUL. Understanding the sensitivity of the estimated RUL to these various uncertainties and aspects is of great importance if RUL is to be estimated as accurately as possible. In this dissertation, a sensitivity analysis is performed with the purpose of establishing the sensitivity of the estimated RUL of the last stage rotor of an LP steam turbine, to the number of harmonics used in a nonlinear harmonic (NLH) CFD simulation. The sensitivity of the estimated RUL is evaluated in the HCF regime, where the cyclic stresses occur below the yield strength of the turbine blade. A CFD model, FE model, and fatigue model were therefore developed in such a manner that would suffice, regarding the purpose of the sensitivity analysis. The CFD model is validated by comparing the predicted CFD power to that of actual generated power of a dual 100MW LP steam turbine. The sensitivity analysis is performed for 3 operation conditions, and for each operational condition the aerodynamic forces were computed using 1, 2, and 3 harmonics in an NLH simulation. The estimation process considers a weak coupling between the CFD model and FE model. NLH simulations are firstly performed to calculate the unsteady static surface pressure distributions on the last stage rotor. This is followed by the mapping thereof to the FE model, for which a transient structural analysis is performed. Finally, the RUL is estimated by performing a fatigue analysis on the stress history obtained from the transient structural analysis. Based on the results of the sensitivity analysis, the following recommendations were made, from a conservative point of view. Firstly, in general, if the RUL is to be estimated with reasonable accuracy, just using 1 harmonic in an NLH simulation will not be sufficient and 2 harmonics should be used. Secondly, if the RUL has to be estimated with high accuracy, 3 harmonics should be used. en_ZA
dc.description.availability Unrestricted en_ZA
dc.description.degree MEng en_ZA
dc.description.department Mechanical and Aeronautical Engineering en_ZA
dc.description.sponsorship National Research Foundation (NRF) en_ZA
dc.identifier.citation Maré, CF 2018, An investigation of CFD simulation for estimation of turbine RUL, MEng Dissertation, University of Pretoria, Pretoria, viewed yymmdd <http://hdl.handle.net/2263/69152> en_ZA
dc.identifier.other A2019
dc.identifier.uri http://hdl.handle.net/2263/69152
dc.language.iso en en_ZA
dc.publisher University of Pretoria
dc.rights © 2019 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.
dc.subject Remaining useful life en_ZA
dc.subject Computational fluid dynamics (CFD) en_ZA
dc.subject Low pressure steam turbine en_ZA
dc.subject Nonlinear harmonics en_ZA
dc.subject High cycle fatigue en_ZA
dc.subject UCTD
dc.title An investigation of CFD simulation for estimation of turbine RUL en_ZA
dc.type Dissertation en_ZA


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