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Research Papers

A Method for Estimating the Influence of Time-Dependent Vane and Blade Pressure Fields on Turbine Rim Seal Ingestion

[+] Author and Article Information
Bruce V. Johnson, Ralf Jakoby

 Alstom Power, CH-5401 Baden, Switzerland

Dieter E. Bohn

Institute of Steam and Gas Turbines, RWTH Aachen University, D-52062 Aachen, Germany

Didier Cunat

 Turbomeca, 64511 Bordes Cedex, France

J. Turbomach 131(2), 021005 (Jan 22, 2009) (10 pages) doi:10.1115/1.2950053 History: Received March 30, 2007; Revised August 24, 2007; Published January 22, 2009

A method of estimating the turbine rim seal ingestion rates was developed using the time-dependent pressure distributions on the hub of turbines and a simple-orifice model. Previous methods use the time-averaged pressure distribution downstream of the vanes to estimate seal ingestion. The present model uses the pressure distribution near the turbine hub, obtained from 2D time-dependent stage calculations, and a simple-orifice model to estimate the pressure-driven ingress of gas-path fluid into the turbine disk cavity and the egress of cavity fluid to the gas path. The time-dependent pressure distribution provides the influence of both the vane wakes and the bow wave from the blade on the pressure difference between the hub pressure at an azimuthal location and the cavity pressure. Results from the simple-orifice model are used to determine the effective Cd that matches the cooling effectiveness at radii near the rim seal with the amount of gas-path-ingested flow required to mix with the coolant flow. Cavity ingestion data from rim seal ingestion experiments in a 1.5-stage turbine and numerical simulations for a 1 vane, 2-blade sector of the 16-vane, 32-blade turbine were used to evaluate the method. The experiments and simulations were performed for close-spaced and wide-spaced half stages between both the vane and blade and between the blade and a trailing teardrop-shaped strut. The comparison of the model with a single Cd for axial gap seals and the experiments showed a reasonable agreement for both close- and wide-spaced stages.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Cross section of the RWTH Aachen University test rig with close-spaced arrangement of airfoils

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Figure 2

Close-spaced (Conf. 1a) and wide-spaced (Conf. 1c) airfoil arrangements for experiments. Axial gap seals are midway between the trailing and leading edges of airfoils.

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Figure 3

Arrangement of airfoils and domains for 2D time-dependent calculations of flow

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Figure 4

Variation of calculated pressure downstream of vane 1 trailing edge with close-spaced (Conf. 1a) and wide-spaced (Conf. 1c) airfoils. Solid line—timer averaged; symbols—instantaneous pressures at five equal times in blade passing cycle; variation for Conf. 1c is barely perceptible.

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Figure 5

Variation of calculated pressure behind Vane 1 with close-spaced airfoils (Conf. 1a) at the upstream and downstream edges of the axial gap seal. The solid line is time averaged; symbols are instantaneous pressures with five blade locations.

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Figure 6

Variation of calculated pressure behind vane 1 with wide-spaced airfoils (Conf. 1c) at locations of the upstream and downstream edges of the axial gap seal. The solid line is time averaged; symbols are instantaneous pressures with five blade locations.

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Figure 7

Variation of calculated pressure behind the blade with close-spaced airfoils (Conf. 1a) at the upstream and downstream edges of the axial gap seal

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Figure 8

Variation of calculated pressure behind the blade with wide-spaced airfoils (Conf. 1c) at the upstream and downstream edges of the axial gap seal

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Figure 9

Comparison of measured and calculated pressure distributions downstream of vane 1 trailing edge with close-spaced airfoils (Conf. 1a). Symbols: measured; heavy line: time averaged; light lines: instantaneous at five blade locations (same calculated results as in Fig. 5).

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Figure 10

Sketch of ingestion and mixing processes in an axial gap rim seal

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Figure 11

Calculated pressure coefficient, Cp (φ), at the upstream edge of seal behind vane 1 with Conf. 1a, OP3, and values of Cp* for the cavity-side pressure used to obtain selected seal cooling effectiveness, η

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Figure 12

Calculated velocity distribution across vane pitch for selected cooling effectiveness; vane 1–blade seal with close-spaced airfoils (Conf. 1a)

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Figure 13

Variation of ingested flow rates and coolant flow rate with assumed cavity pressure ratio, Cp*. Axial gap seal downstream of vane 1 with close-spaced airfoils (Conf. 1a); flow condition OP3; open symbols are ingress V*in(ΩR) ratios.

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Figure 14

Evaluation of Cd for simple-orifice model from data calculated for vane 1–blade seal with Conf. 1a and OP3; data from OP1, OP3, and OP4 experimental flow conditions

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Figure 15

Comparison of simple–orifice model with data for vane 1–blade seal and Conf. 1a and with turbulent transport model

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Figure 16

Comparison of simple-orifice model with data for blade–vane 2 seal and Conf. 1c and with turbulent transport model

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