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
Detached-eddy simulation applied to the tip-clearance flow in a last stage steam turbine blade
KTH, School of Industrial Engineering and Management (ITM), Energy Technology. (Turbomachinery Group)
KTH, School of Industrial Engineering and Management (ITM), Energy Technology. (Turbomachinery Group)
2018 (English)In: ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, Oslo, Norway, 2018, Vol. 8Conference paper, Published paper (Refereed)
Abstract [en]

Prediction of the aerodynamic stability of rotor blades at the last stage of steam turbines is of great importance and widely studied. Considering the large span and low natural frequency of these blades, flow at the tip region has a remarkable effect on blade flutter characteristics. However, the transonic tip-clearance flow in these blades has a complex structure of vortices. To obtain a deep understanding of the transonic tip-clearance flow structure in steam turbines, the Detached-Eddy Simulation (DES) is applied in this paper. DES is a hybrid LES/RANS method that activates LES in specified flow regions and applies URANS in other regions of the flow field. As far as we are aware, the tip-clearance flow structure of real-scale last stage steam turbine by high-fidelity numerical method had not been much analyzed in open literature. In this paper, the transonic tip-clearance flow structure in modern last stage of steam turbines is analyzed by both URANS and DES approaches. The open steam turbine model designed by Durham University is chosen as the research model. The flow solver applied is the commercial software ANSYS CFX. From the DES result, the tip leakage vortex and the induced vortices are presented. Based on the comparison between tip-clearance flow structure captured by the two approaches, the URANS method is not able to resolve all induced vortices. Therefore, the distribution of aerodynamic loading on the blade surface is different between URANS and DES results. The present study serves as a basis for investigating the influence of the tip-clearance flow structure on blade aeroelasticity.

Place, publisher, year, edition, pages
Oslo, Norway, 2018. Vol. 8
Keywords [en]
Steam turbine, Tip clearance flow, Detached-Eddy Simulation
National Category
Engineering and Technology
Research subject
Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-233773DOI: 10.1115/GT2018-75943ISI: 000457071200043Scopus ID: 2-s2.0-85053899767ISBN: 9780791851173 (print)OAI: oai:DiVA.org:kth-233773DiVA, id: diva2:1242529
Conference
ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, GT 2018, Oslo, Norway, 11 June 2018 through 15 June 2018
Note

QC 20180829

Available from: 2018-08-28 Created: 2018-08-28 Last updated: 2019-11-13Bibliographically approved
In thesis
1. Improved Flutter Prediction for Turbomachinery Blades with Tip Clearance Flows
Open this publication in new window or tab >>Improved Flutter Prediction for Turbomachinery Blades with Tip Clearance Flows
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Recent design trends in steam turbines strive for high aerodynamic loading and high aspect ratio to meet the demand of higher efficiency. These design trends together with the low structural frequency in last stage steam turbines increase the susceptibility of the turbine blades to flutter. Flutter is the self-excited and self-sustained aeroelastic instability phenomenon, which can result in rapid growth of blade vibration amplitude and eventually blade failure in a short period of time unless adequately damped. To prevent the occurrences of flutter before the operation of new steam turbines, a compromise between aeroelastic stability and stage efficiency has to be made in the steam turbine design process. Due to the high uncertainty in present flutter prediction methods, engineers use large safety margins in predicting flutter which can rule out designs with higher efficiency. The ability to predict flutter more accurately will allow engineers to push the design envelope with greater confidence and possibly create more efficient steam turbines.

The present work aims to investigate the influence of tip clearance flow on the prediction of steam turbine flutter characteristics. Tip clearance flow effect is one of the critical factors in flutter analysis for the majority of aerodynamic work is done near the blade tip. Analysis of the impact of tip clearance flow on steam turbine flutter characteristics is therefore needed to formulate a more accurate aeroelastic stability prediction method in the design phase.Besides the tip leakage vortex, the induced vortices in the tip clearance flow can also influence blade flutter characteristics. However, the spatial distribution of the induced vortices cannot be resolved by URANS method for the limitation of turbulence models. The Detached-Eddy Simulation (DES) calculation is thus applied on a realistic-scale last stage steam turbine model to analyze the structure of induced vortices in the tip region. The influence of the tip leakage vortex and the induced vortices on flutter prediction are analyzed separately.

The KTH Steam Turbine Flutter Test Case is used in the flutter analysis as a typical realistic-scale last stage steam turbine model. The energy method based on 3D unsteady CFD calculation is applied in the flutter analysis. Two CFD solvers, an in-house code LUFT and a commercial software ANSYS CFX, are used in the flutter analysis as verification of each other. The influence of tip leakage vortex on the steam turbine flutter prediction is analyzed by comparing the aeroelastic stability of two models: one with the tip gap and the other without the tip gap. Comparison between the flutter characteristics predicted by URANS and DES approaches is analyzed to investigate the influence of the induced vortices on blade flutter characteristics.

The multiple induced vortices and their relative rotation around the tip leakage vortex in the KTH Steam Turbine Flutter Test Case are resolved by DES but not by URANS simulations. Both tip leakage vortex and induced vortices have an influence on blade loading on the rear half of the suction side near the blade tip. The flutter analysis results suggest that the tip clearance flow has a significant influence on blade aerodynamic damping at the least stable interblade phase angle (IBPA), while its influence on the overall shape of the damping curve is minor. At the least stable IBPA, the tip leakage vortex shows a stabilization effect on rotor aeroelastic stabilities while the induced vortices show a destabilization effect on it. Meanwhile, a non-linear unsteady flow behavior is observed due to the streamwise motion of induced vortices during blade oscillation, which phenomenon is only resolved in DES results.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2018. p. 88
Series
TRITA-ITM-AVL ; 2018:40
Keywords
Steam turbine, Flutter, Aeroelastic stability, Tip clearance flow, Detached-Eddy Simulation
National Category
Engineering and Technology
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-233770 (URN)978-91-7729-909-7 (ISBN)
Presentation
2018-09-18, HPT Learning Theater, M235, Brinellvägen 68, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Available from: 2018-08-28 Created: 2018-08-28 Last updated: 2018-08-28Bibliographically approved

Open Access in DiVA

No full text in DiVA

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Sun, TianruiPetrie-Repar, Paul
By organisation
Energy Technology
Engineering and Technology

Search outside of DiVA

GoogleGoogle Scholar

doi
isbn
urn-nbn

Altmetric score

doi
isbn
urn-nbn
Total: 299 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