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Research Papers

The Influence of the Total Pressure Profile on the Performance of Axial Gas Turbine Diffusers

[+] Author and Article Information
A. Hirschmann

ITSM–Institute of Thermal Turbomachinery and Machinery Laboratory, Universität Stuttgart, Pfaffenwaldring 6, D-70569 Stuttgart, Germanyhirschmann@itsm.uni-stuttgart.de

S. Volkmer

ITSM–Institute of Thermal Turbomachinery and Machinery Laboratory, Universität Stuttgart, Pfaffenwaldring 6, D-70569 Stuttgart, Germanyvolkmer@itsm.uni-stuttgart.de

M. Schatz

ITSM–Institute of Thermal Turbomachinery and Machinery Laboratory, Universität Stuttgart, Pfaffenwaldring 6, D-70569 Stuttgart, Germanyschatz@itsm.uni-stuttgart.de

C. Finzel

ITSM–Institute of Thermal Turbomachinery and Machinery Laboratory, Universität Stuttgart, Pfaffenwaldring 6, D-70569 Stuttgart, Germanyfinzel@itsm.uni-stuttgart.de

M. Casey

ITSM–Institute of Thermal Turbomachinery and Machinery Laboratory, Universität Stuttgart, Pfaffenwaldring 6, D-70569 Stuttgart, Germanycasey@itsm.uni-stuttgart.de

M. Montgomery

 Siemens Energy, Inc., Jupiter, FLmontgomery.matthew@siemens.com

J. Turbomach 134(2), 021017 (Jun 29, 2011) (9 pages) doi:10.1115/1.4003064 History: Received July 12, 2010; Revised July 28, 2010; Published June 29, 2011; Online June 29, 2011

Large industrial gas turbines for combined heat and power generation normally have axial diffusers leading to the heat recovery steam generator. The diffusers operate with high inlet axial Mach number (0.6) and with a nonuniform inlet total pressure profile from the turbine. Tests have been carried out on a generic highly loaded axial diffuser in a scaled axial diffuser test rig, with different inlet total pressure profiles including those that might be met in practice. The results show that the inlet total pressure profile has a strong effect on the position of flow separation, whereby a hub-strong profile tends to separate at the casing and the tip-strong profile on the hub. Steady computational fluid dynamics (CFD) simulations using the shear stress transport (SST) turbulence model have been carried out based on extensive studies of the best way to model the inlet boundary conditions. These simulations provide good agreement with the prediction of separation in the diffuser but the separated regions often persist too long so that, in this highly loaded case with flow separation, the calculated diffuser pressure recovery can be in error by up to 30%.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Cross section through the axial diffuser test rig

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Figure 2

Scheme of the diffuser with the position of the pressure taps on the walls and the planes of probe measurement

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Figure 3

Drag body composed of pins and wire (a) tip-strong and (b) hub-strong total pressure profile

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Figure 4

Total pressure distribution at the diffuser inlet for the uniform, tip-strong, and hub-strong cases at Mach 0.6

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Figure 5

Turbulence level at the first measurement plane (S1) at the inlet of the diffuser

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Figure 6

Vector plot of the flow velocity in the measurement planes for (a) the tip-strong, (b) the uniform, and (c) the hub-strong total pressure profiles at the inlet of the diffuser

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Figure 7

Pressure recovery calculated with the static pressure at the diffuser walls for the different total pressure profiles at a Mach number of 0.6

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Figure 8

Pressure recovery calculated of the data of the probe measurement for the three inlet total pressure profiles and two different Mach numbers

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Figure 16

Computed pressure recovery along the axial direction with different inlet profiles and inlet Mach numbers

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Figure 17

Radial distributions of standardized pressure computed with 2D and 3D models in plane S2 with tip-strong profile and Minlet=0.25

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Figure 18

Isoline of axial velocity u=0 m/s with tip-strong profile and Mach number Minlet=0.6 for 2D and 3D models

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Figure 19

(a) Radial distributions of computed and measured total pressure (tip-strong profile), (b) Mach number Minlet=0.6 in planes S1 and S2, and ratio of computed total pressure profiles

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Figure 20

Contour plots of standardized axial velocity computed with measured and shifted inlet total pressure profile

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Figure 15

Radial distributions of computed and measured (a) Mach number and (b) standardized static pressure at traverses at S5 for case with tip-strong profile and Minlet=0.25

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Figure 14

Radial distributions of computed and measured Mach number at traverses at plane (a) S2 and (b) S5 for case with tip-strong profile and Minlet=0.6

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Figure 13

Contour plots of standardized axial velocity with different inlet profiles and Minlet=0.25 and Minlet=0.6

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Figure 12

(a) Ratio of computed cp and cp,max computed with grid 3 in plane S5 and (b) ratio of computed and measured cp in plane S5 with 3D model

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Figure 11

Diffuser annular part and measurement planes S1–S3

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Figure 10

Computational domain for the 2D and 3D models

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Figure 9

Velocity vectors in the measurement planes for the hub-strong total pressure profile at a Mach number of 0.25

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