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Research Papers

Impact of the Inflow Conditions on the Heavy-Duty Gas Turbine Exhaust Diffuser Performance

[+] Author and Article Information
Vladimir Vassiliev

 Alstom (Switzerland) Ltd., CH-5401 Baden, Switzerlandvladimir.vassiliev@power.alstom.com

Stefan Irmisch

Testing and Validation, Alstom (Switzerland) Ltd., CH-5401 Baden, Switzerlandstefan.a.irmisch@power.alstom.com

Samer Abdel-Wahab

 Alstom Power, Jupiter, FL 33458samer.abdel-wahab@power.alstom.com

Andrey Granovskiy

Aerodynamics Department, Alstom Power Uniturbo, 129626 Moscow, Russiaandrei.granovsky@power.alstom.com

J. Turbomach 134(4), 041018 (Jul 25, 2011) (9 pages) doi:10.1115/1.4003714 History: Received October 17, 2010; Revised December 02, 2010; Published July 25, 2011; Online July 25, 2011

The flow in exhaust diffusers along with the channel geometry strongly depends on the inflow conditions, including Mach number level, total pressure distribution, flow angle, and turbulence. In the first part of this paper, the impact of these parameters is analyzed using computational fluid dynamics, experimental data from the test rig, and field measurements. A widespread opinion is that the optimal condition for the diffuser is an axial uniform inflow. However, it is shown in this paper that nonuniform pressure distribution compared with a uniform one can lead to better diffuser performance and that a moderate residual swirl can improve the performance as well. In the second part of this paper, the minimization of exhaust losses in heavy-duty gas turbines is discussed and illustrated by two practical examples.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Theoretical contour of the optimum 2D diffuser (according to Ref. 6)

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Figure 2

Schematic of exhaust diffuser investigated in Ref. 13

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Figure 3

Pressure recovery versus inlet Mach number

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Figure 4

Normalized outlet blockage coefficient versus inlet Mach number

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Figure 5

Typical heavy-duty gas turbine exhaust diffuser characteristic (symbols, results of measurements; dotted line, trend line based on measurements; solid line, numerical calculations, where the loss and reduced mass flow at point A have been applied as reference values; B, operation with compressor up-flow)

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Figure 6

Normalized total pressure at diffuser inlet

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Figure 7

Normalized total pressure inside diffuser (2D calculations without struts)

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Figure 8

Mach number distribution downstream the first row of struts (3D calculations with struts, whose position is indicated in Fig. 2)

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Figure 9

Pressure recovery

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Figure 10

Swirl angle distribution at the diffuser inlet tested in Ref. 13 (different IGV positions and different Mach numbers)

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Figure 11

Pressure recovery versus swirl angle

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Figure 12

Exhaust loss for two different struts (symbols, results of measurements; thin solid lines, trend lines based on measurements; thick solid line, numerical calculations of redesign; dotted curve, calculated loss at constant Cp)

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Figure 13

Approximation of turbulence parameters in boundary layer: (a) turbulent kinetic energy and (b) Reynolds stresses

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Figure 14

Residual swirl angle at diffuser inlet (solid line, original design intent; symbols, measurements in test engine at conditions A and B)

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Figure 15

Exhaust loss split

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Figure 16

Schematic of exhaust diffuser

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Figure 17

(a) Existing strut and (b) considered modification

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Figure 18

Comparison of inflow conditions (symbols, measurements; lines, CFD analysis)

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Figure 19

Exhaust diffuser characteristic

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