Research Papers

Unsteady Aerodynamics of Low-Pressure Steam Turbines Operating Under Low Volume Flow

[+] Author and Article Information
Benjamin Megerle

Alstom Power,
Baden 5401, Switzerland
e-mail: benjamin.megerle@power.alstom.com

Ivan McBean

Alstom Power,
Baden 5401, Switzerland

Timothy Stephen Rice

Alstom Power,
Rugby CV21 2NH, UK

Peter Ott

Group of Thermal Turbomachinery, EPFL,
Lausanne 1015, Switzerland

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received November 5, 2013; final manuscript received December 20, 2013; published online May 2, 2014. Editor: Ronald Bunker.

J. Turbomach 136(9), 091008 (May 02, 2014) (8 pages) Paper No: TURBO-13-1252; doi: 10.1115/1.4027373 History: Received November 05, 2013; Revised December 20, 2013

Nonsynchronous excitation under low volume operation is a major risk to the mechanical integrity of last stage moving blades (LSMBs) in low-pressure (LP) steam turbines. These vibrations are often induced by a rotating aerodynamic instability similar to rotating stall in compressors. Currently extensive validation of new blade designs is required to clarify whether they are subjected to the risk of not admissible blade vibration. Such tests are usually performed at the end of a blade development project. If resonance occurs a costly redesign is required, which may also lead to a reduction of performance. It is therefore of great interest to be able to predict correctly the unsteady flow phenomena and their effects. Detailed unsteady pressure measurements have been performed in a single stage model steam turbine operated with air under ventilation conditions. 3D computational fluid dynamics (CFD) has been applied to simulate the unsteady flow in the air model turbine. It has been shown that the simulation reproduces well the characteristics of the phenomena observed in the tests. This methodology has been transferred to more realistic steam turbine multistage environment. The numerical results have been validated with measurement data from a multistage model LP steam turbine operated with steam. Measurement and numerical simulation show agreement with respect to the global flow field, the number of stall cells and the intensity of the rotating excitation mechanism. Furthermore, the air model turbine and model steam turbine numerical and measurement results are compared. It is demonstrated that the air model turbine is a suitable vehicle to investigate the unsteady effects found in a steam turbine.

Copyright © 2014 by ASME
Your Session has timed out. Please sign back in to continue.



Grahic Jump Location
Fig. 1

LSMB tip pressure ratio as a function of volume flow

Grahic Jump Location
Fig. 2

Meridional flow field

Grahic Jump Location
Fig. 3

Model steam turbine at low volume flow LSMB inlet flow angles with 0 deg referring to axial flow

Grahic Jump Location
Fig. 4

Rotating stall mechanism in axial compressors

Grahic Jump Location
Fig. 5

(a) Cross-sectional view of the model steam turbine rear stage, (b) upstream view of plane 62, probe traverse locations S05, S06 and S07

Grahic Jump Location
Fig. 6

Expansion lines for different volume flows, four stage CFD result—steam model turbine

Grahic Jump Location
Fig. 7

FFT analysis of 10 rotor revolutions, static pressure in plane 61 at 95% span height

Grahic Jump Location
Fig. 8

CFD model with realistic exhaust configuration

Grahic Jump Location
Fig. 9

Time averaged flow field downstream of the model steam turbine LSMB in plane 62, see Fig. 5

Grahic Jump Location
Fig. 10

Circumferentially averaged meridional stream lines from CFD at vx/uhub = 0.06

Grahic Jump Location
Fig. 11

Normalized pressure amplitude (RMS) of the dominate cell patterns over span downstream of the LSMB air model

Grahic Jump Location
Fig. 12

Unsteady pressure traverses for CFD and measurement, pressure amplitude of dominant cell pattern at vx/uhub = 0.06

Grahic Jump Location
Fig. 13

Blade to blade view at 70% span with radial velocity contour normalized with uhub and projected flow vectors at vx/uhub = 0.06

Grahic Jump Location
Fig. 14

Axial wall shear on LSMB blade surface looking down stream, regions with negative wall shear indicate separated flow (steam model) at vx/uhub = 0.06




Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In