Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Experimental Investigation of Performance, Flow Interactions and Rotor Forcing in Axial Partial Admission Turbines
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.ORCID iD: 0000-0002-1033-9601
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thesis comprises a collection of four papers with preceding summary and supplementary appendices. The core investigation solely is of experimental nature although reference and comparisons with numerical models will be addressed. The first admission stage in an industrial steam turbine is referred to as the control stage if partial admission is applied. In order to achieve high part load efficiency and a high control stage output it is routinely applied in industrial steam turbines used in combined heat and power plants which frequently operate at part load. The inlet flow is individually throttled into separate annular arcs leading to the first stator row. Furthermore, partial admission is sometimes used in small-scale turbine stages to avoid short vanes/blades in order to reduce the impact from the tip leakage and endwall losses. There are three main aspects regarding partial admission turbines that need to be addressed. Firstly, there are specific aerodynamic losses: pumping-, emptying- and filling losses attributed to the partial admission stage. Secondly, if it is a multistage turbine, the downstream stages experience non-periodic flow around the periphery and circumferential pressure gradients and flow angle variations that produce additional mixing losses. Thirdly, the aeromechanical condition is different compared to full admission turbines and the forcing on downstream components is also circumferentially non-periodic with transient load changes. Although general explanations for partial admission losses exist in open literature, details and loss mechanisms have not been addressed in the same extent as for other sources of losses in full admission turbines. Generally applicable loss correlations are still lacking. High cycle fatigue due to unforeseen excitation frequencies or due to under estimated force magnitudes, or a combination of both causes control stage breakdowns. The main objectives of this thesis are to experimentally explore and determine performance and losses for a wide range of partial admission configurations. And, to perform a forced response analysis from experimental data for the axial test turbine presented herein in order to establish the forced response environment and identify particularities important for the design of control stages. Performance measurements concerning the efficiency trends and principal circumferential and axial pressure distortions demonstrate the applicability of the partial admission setup employed in the test turbine. Findings reveal that the reaction degree around the circumference varies considerably and large flow angle deviations downstream of the first rotor are present, not only in conjunction to the sector ends but stretching far into the admission sector. Furthermore, it is found that the flow capacity coefficient increases with reduced admission degree and the filling process locally generates large rotor incidence variation associated with high loss. Moreover, the off design conditions and efficiency deficit of downstream stages are evaluated and shown to be important when considering the overall turbine efficiency. By going from one to two arcs at 52.4% admission nearly a 10% reduction in the second stage partial admission loss, at design operating point was deduced from measurements. Ensemble averaged results from rotating unsteady pressure measurements indicate roughly a doubling of the normalized relative dynamic pressure at rotor emptying compared to an undisturbed part of the admission jet for 76.2% admission. Forced response analysis reveals that a large number of low engine order force impulses are added or highly amplified due to partial admission because of the blockage, pumping, loading and unloading processes. For the test turbine investigated herein it is entirely a combination of number of rotor blades and low engine order excitations that cause forced response vibrations. One possible design approach in order to change the force spectrum is to alter the relationship between admitted and non-admitted arc lengths.

Abstract [sv]

Denna sammanläggningsavhandling består av fyra artiklar och föregås av en sammanfattning med kompletterande bilagor. Kärnan av undersökningen är experimentell även om referenser och jämförelser med numeriska modeller förekommer där så bedöms lämpligt. Det första steget i en industriell ångturbin kallas reglersteg om partialpådrag tillämpas. Det används rutinmässigt i kraftvärmeanläggningar som ofta körs vid dellaster för att åstadkomma en hög dellastverkningsgrad och hög stegeffekt. Inloppsflödet delas in separata och individuellt strypreglerade pådragsbågar som leder till det första munstycksgittret. Ibland används partialpådrag i små turbiner för att undvika korta blad och på så sätt minska takläckage och ändväggsförlusternas inflytande på den totala förlusten. Det finns i huvudsak tre aerodynamiska/aeromekaniska egenheter som bör beaktas. Först det första är det speciella aerodynamiska förluster associerade till partialpådrag eller reglersteget: ventilations-, tömnings och fyllningsförluster. För det andra, om det är en flerstegsturbin påverkas också nedströms steg negativt av det asymmetriska flödet runt omkretsen som innefattar stora tryckvariationer och flödesvinkelvariationer. För det tredje är den aeromekaniska situationen speciell jämfört med ett fullpådraget steg. För partialpådrag existerar dynamiska krafter med snabba laständringar vid in och utpassering i pådragsbågen. Även om det existerar generella förklaringar i den öppna litteraturen angående förluster så har inte förlustmekanismerna utretts i samma omfattning jämfört med fullpådrag. Ingen generell förlustkorrelation finns. Utmattning på grund oförutsedda excitationsfrekvenser, underskattade kraftamplituder eller en kombination av båda orsakar reglerstegshaveri för ångturbinintressenter. De huvudsakliga målsättningarna med denna studie är att experimentellt utforska och bestämma prestanda och förluster för ett stort antal partialpådragskonfigurationer. Samt att genomföra en vibrationsanalys (relaterat till aerodynamiska kraftimpulser) utifrån mätdata från provturbinen avhandlad häri. Detta för att kartlägga de aeromekaniska förutsättningarna och om möjligt identifiera egenheter viktiga för konstruktion av reglersteg. Prestandamätningar rörande verkningsgradstrender och generella strömningsvariationer runt omkretsen bekräftar resultat från den öppna litteraturen och därmed demonstrerar dugligheten av den partialpådragskonfiguration som används i luftprovturbinen. Dessutom visar resultaten bland annat att reaktionsgraden varierar kraftigt runt omkretsen med stora variationer i rotorns utloppsvinkel inte enbart i anslutning till sektorändar utan långt in i pådragssektorn. Flödeskapacitetskoefficienten eller turbinkonstanten ökar med minskat pådrag och fyllningsprocessen genererar stora variationer i rotorns inloppsvinkel förknippade med höga förluster. Det är viktigt att beakta dellastförutsättningarna och verkningsgradsminskningen för nedströms steg. Genom att använda två pådragsbågar istället för en för ett givet pådrag av 52,4% minskar partialpådragsförlusterna för nedströmssteget med nästan 10 % vid designpunkten, härlett från mätningar. Samlade medelvärden från roterande instationära mätningar visar på en fördubbling av det relativa dynamiska trycket vid rotortömning jämfört med en opåverkad del av pådragsbågen. Vibrationsanalys (relaterat till aerodynamiska kraftimpulser) av mätdata avslöjar att partialpådrag orsakar en stor mängd kraftimpulser med låga varvtalsmultiplar, främst från ventilationen och påavlastningsprocesserna. För provturbinen så är det helt och hållet kombinationer mellan antalet rotorblad och dessa kraftimpulser som orsakar strömningspåverkade vibrationer. Ett möjligt tillvägagångssätt konstruktionsmässigt för att ändra kraftspektrumet är att ändra längförhållandet mellan pådragen och blockerad del.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , xvi, 69 p.
Series
Trita-KRV, ISSN 1100-7990 ; 12:01
Keyword [en]
axial turbine, partial admission, part loads, experimental investigation, turbine performance, losses, dynamic rotor forces, forced response, unsteady flow
Keyword [sv]
axialturbin, partialpådrag, dellaster, reglersteg, experimentell undersökning, turbinprestanda, förluster, dynamiska krafter, rotorvibration, instationär strömning
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-53699ISBN: 978-91-7501-224-7 (print)OAI: oai:DiVA.org:kth-53699DiVA: diva2:470709
Public defence
2012-01-19, D2, Lindstedtsvägen 5, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120109Available from: 2012-01-09 Created: 2011-12-29 Last updated: 2012-03-23Bibliographically approved
List of papers
1. An experimental study on partial admission in a two-stage axial air test turbine with numerical comparisons
Open this publication in new window or tab >>An experimental study on partial admission in a two-stage axial air test turbine with numerical comparisons
2004 (English)In: Proceedings of the ASME Turbo Expo 2004, Vienna, 2004, Vol. 5 B, 1285-1297 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents ongoing experimental aerodynamic and efficiency measurements on a cold flow two-stage axial air test turbine with low reaction steam turbine blades at different degrees of partial admission. The overall objectives of the work are to experimentally investigate and quantify the steady and unsteady aerodynamic losses induced by partial admission. The first results show that both the total-to-static turbine efficiency drops and that the efficiency peak appears at lower isentropic velocity ratios with lower degrees of admission. Detailed steady traverse measurements of the static wall pressures downstream of sector-ends show strong local variations. The pressure wake from the partial admission blockage moves almost axially through the turbine while the temperature wake is located in a tangential position that represents the position of a particle trace based on velocity triangles, in the direction of the rotor rotation. Comparisons with 2D compressible flow computations around the circumference demonstrate the importance of the radial flow component in these experiments.

Place, publisher, year, edition, pages
Vienna: , 2004
Series
2004 ASME Turbo Expo
Keyword
Computational complexity, Mathematical models, Numerical analysis, Pressure effects, Steam, Thermodynamics, Turbomachine blades, Air test turbines, Radial flow components, Rotor rotations, Tangential position, Turbines
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-53550 (URN)2-s2.0-10244255167 (Scopus ID)
Note
Sponsors: ASME, International Gas Turbine Institute. QC 20120109Available from: 2011-12-28 Created: 2011-12-28 Last updated: 2012-01-09Bibliographically approved
2. REDUNDANT ROTATING MEASUREMENTS IN AN AXIAL COLD FLOW TEST TURBINE: Development and Procedure
Open this publication in new window or tab >>REDUNDANT ROTATING MEASUREMENTS IN AN AXIAL COLD FLOW TEST TURBINE: Development and Procedure
2006 (English)Conference paper, Published paper (Other academic)
Abstract [en]

A rotating measurement system has been designed and commissioned for a cold flow test turbine and tested under the influence of partial admission. A shrouded turbine rotor of impulse design is equipped with miniature pressure transducers and strain gauges. This paper discusses the selected experimental design and procedure. Overall, the first test runs went well and necessary data were collected and could be evaluated accordingly. Encountered specific measurement technique problems are addressed where the importance of high redundancy is stressed. Results demonstrate one effect that imbedded sensor technology may encounter as regards of dynamic measurements and calibrations.

Keyword
rotating measurements, high speed acquisition
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-53561 (URN)
Conference
The XVIII Symposium on Measuring Techniques in Turbomachinery, Thessaloniki, Greece 2006
Note
Qc 201200117Available from: 2012-01-17 Created: 2011-12-28 Last updated: 2012-03-23Bibliographically approved
3. DYNAMIC FEATURES OF PARTIAL ADMISSION: OUTCOMES FROM ROTATING MEASUREMENTS
Open this publication in new window or tab >>DYNAMIC FEATURES OF PARTIAL ADMISSION: OUTCOMES FROM ROTATING MEASUREMENTS
2007 (English)In: Euroturbo 7: Proceedings of the 7th European Conference on Turbomachinery, Fluid Dynamics and Thermodynamics, Athens: Local Conference Organising Committee , 2007, 451-462 p.Conference paper, Published paper (Refereed)
Abstract [en]

A system for rotating measurements has been designed and commissioned for a two-stage axial turbine of impulse design. Relative total pressure and strain gauge measurements in the rotating frame of reference have been performed during partial admission tests in this turbine. The overall project objectives are to determine unsteady aerodynamic losses related to admission sector-ends and rotor forcing functions. Some outcomes are presented and discussed herein. The unsteadiness in the measured relative total pressure is observed to be largest downstream of the suction side of the partial admission blockage where the high momentum fluid vividly interacts with the rotor. Strain gauge results show a high strain peak downstream of the suction side of the blockage. When reducing the shaft speed at constant pressure ratio, the dip in relative total pressure and the peak in tensile strain, that occur when a blade enters the blocked region, are shifted in the counter rotational direction. This is believed to reflect earlier emptying of the rotor blade channel. Furthermore, an increase of the flow capacity coefficient with a decrease of admission degree has been observed.

Place, publisher, year, edition, pages
Athens: Local Conference Organising Committee, 2007
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-53636 (URN)2-s2.0-84925308758 (Scopus ID)
Conference
7th European Conference on Turbomachinery, Fluid Dynamics and Thermodynamics
Note
QC 20120117Available from: 2012-01-17 Created: 2011-12-29 Last updated: 2012-03-22Bibliographically approved
4. Forced Response in axial turbines under the influence of partial admission
Open this publication in new window or tab >>Forced Response in axial turbines under the influence of partial admission
2012 (English)In: ASME Turbo Expo 2012 - Turbine Technical Conference and Exposition, Copenhagen, June 11-15, 2012: Volume 7, Issue PARTS A AND B, 2012, ASME Press, 2012, 1419-1429 p.Conference paper, Published paper (Refereed)
Abstract [en]

High cycle fatigue (HCF) due to unforeseen excitation frequencies or due to under predicted force magnitudes, or a combination of both causes control stage failures for steam turbine stakeholders. The objectives of this paper is to provide an extended design criteria toolbox and validation data for control stage design based on experimental data, with the aim to decrease HCF incidents for partial admission turbines. The upstream rotor in a two stage air test turbine is instrumented with pressure transducers and strain gauges. Admission degrees stretching from 28.6% to 100% as one or two admission arcs are simulated by blocking segmental arcs immediately upstream of first stator vanes by aerodynamically shaped filling blocks. Sweeps across a speed range from 50 to 105% of design speed are performed at constant turbine pressure ratio during simultaneous high speed acquisition. A forced response analysis is performed and results presented in Campbell diagrams. Partial admission creates a large number of low engine order forced responses because of the blockage, pumping, loading and unloading processes. Combinations of the number of rotor blades and low engine order excitations are the principal sources of forced response vibrations for the turbine studied herein. Altering the stator and/or rotor pitches will change the excitation pattern. A relation between the circumferential lengths of the admitted and non-admitted arcs that dictates the excitation forces is observed that may serve as a design parameter.

Place, publisher, year, edition, pages
ASME Press, 2012
Series
Proceedings of the ASME Turbo Expo, 7
Keyword
Engine order excitations, Excitation frequency, Excitation pattern, Experimental datum, Forced response analysis, High cycle fatigue, High speed acquisition, Loading and unloading
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-53665 (URN)10.1115/GT2012-68303 (DOI)000335868800141 ()2-s2.0-84881165627 (Scopus ID)978-079184473-1 (ISBN)
Conference
ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, GT 2012; Copenhagen; Denmark; 11 June 2012 through 15 June 2012
Funder
StandUp
Note

QC 20120109

Available from: 2011-12-29 Created: 2011-12-29 Last updated: 2014-10-08Bibliographically approved

Open Access in DiVA

Dr thesis, Jens Fridh(5788 kB)4123 downloads
File information
File name FULLTEXT01.pdfFile size 5788 kBChecksum SHA-512
aa26bfccd387eb5923fc0f3c54a91c907b280dcc513f95847392865616159f99f1b324bbb2161b9ed65b8953090a954270cb84d778d3658644a903a6917ce999
Type fulltextMimetype application/pdf
errata(133 kB)153 downloads
File information
File name ERRATA01.pdfFile size 133 kBChecksum SHA-512
5b4c734f6561b387f776500c25cedbfbd8ce78442bf93563e60d4292ea1fcb4226bfcb13db4ac75222459691a59d5028ff1b54122d2a717845a16982f8dbd5ba
Type errataMimetype application/pdf

Search in DiVA

By author/editor
Fridh, Jens
By organisation
Heat and Power Technology
Energy Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 4123 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 1751 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf