Research Papers: Gas Turbines: Turbomachinery

Efficient Methods for Predicting Low Pressure Steam Turbine Exhaust Hood and Diffuser Flows at Design and Off-Design Conditions

[+] Author and Article Information
Zoe Burton

School of Engineering and Computing Sciences,
Durham University,
South Road,
Durham DH1 3LE, UK
e-mail: zoe.burton@hotmail.co.uk

Grant Ingram

School of Engineering and Computing Sciences,
Durham University,
South Road,
Durham DH1 3LE, UK
e-mail: g.l.ingram@durham.ac.uk

Simon Hogg

School of Engineering and Computing Sciences,
Durham University,
South Road,
Durham DH1 3LE, UK
e-mail: simon.hogg@durham.ac.uk

1Present address: Jaguar Land Rover, Banbury Road, Gaydon CV35 0BJ, UK.

2Corresponding author.

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received September 22, 2014; final manuscript received January 7, 2015; published online February 3, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(8), 082601 (Aug 01, 2015) (11 pages) Paper No: GTP-14-1557; doi: 10.1115/1.4029599 History: Received September 22, 2014; Revised January 07, 2015; Online February 03, 2015

The exhaust hood of a steam turbine is an important area of turbomachinery research as its performance strongly influences the power output of the last stage blades (LSB). This paper compares results from 3D simulations using a novel application of the nonlinear harmonic (NLH) method with more computationally demanding predictions obtained using frozen rotor techniques. Accurate simulation of exhausts is only achieved when simulations of LSB are coupled to the exhaust hood to capture the strong interaction. One such method is the NLH method. In this paper, the NLH approach is compared against the current standard for capturing the inlet circumferential asymmetry, the frozen rotor approach. The NLH method is shown to predict a similar exhaust hood static pressure recovery and flow asymmetry compared with the frozen rotor approach using less than half the memory requirement of a full annulus calculation. A second option for reducing the computational demand of the full annulus frozen rotor method is explored where a single stator passage is modeled coupled to the full annulus rotor by a mixing plane. Provided the stage is choked, this was shown to produce very similar results to the full annulus frozen rotor approach but with a computational demand similar to that of the NLH method. In terms of industrial practice, the results show that for a typical well designed exhaust hood at nominal load conditions, the pressure recovery predicted by all methods (including those which do not account for circumferential uniformities) is similar. However, this is not the case at off-design conditions where more complex interfacing methods are required to capture circumferential asymmetry.

Copyright © 2015 by ASME
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Fig. 1

Vortices and complex exhaust hood flow structure

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Fig. 2

Diagram of stage and exhaust hood interfaces

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Fig. 3

Flow profiles applied at stator inlet [9]

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Fig. 4

Periodic perturbations in LSB and exhaust hood

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Fig. 5

Pt and swirl at the rotor outlet plane

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Fig. 6

P contours at stator outlet plane for three interface treatments (Pa)

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Fig. 7

P contours at rotor outlet plane for three interface treatments (Pa)

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Fig. 8

Midspan P variations around the rotor outlet plane

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Fig. 9

RMSP at the rotor outlet plane for three methods (Pa)

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Fig. 10

P blade-to-blade contours at midspan (Pa)

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Fig. 11

Cp for the exhaust hood system (diffuser and hood)

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Fig. 12

Cp for the exhaust diffuser, hood and system

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Fig. 13

Pt contours at meridional plane using full annulus frozen rotor approach at a range of mass flow rates (Pa)

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Fig. 14

Swirl angle distributions at exhaust hood inlet plane at nominal load and off design (deg)

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Fig. 15

RMSSwirl at the exhaust hood inlet plane (deg)




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