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Research Papers

The Influence of Shroud and Cavity Geometry on Turbine Performance: An Experimental and Computational Study— Part II: Exit Cavity Geometry

[+] Author and Article Information
Budimir Rosic

Whittle Laboratory,  Cambridge University, Cambridge CB30DY, UKbr241@cam.ac.uk

John D. Denton, Eric M. Curtis, Ashley T. Peterson

Whittle Laboratory,  Cambridge University, Cambridge CB30DY, UK

J. Turbomach 130(4), 041002 (Jun 17, 2008) (10 pages) doi:10.1115/1.2777202 History: Received June 18, 2007; Revised June 19, 2007; Published June 17, 2008

The geometry of the exit shroud cavity where the rotor shroud leakage flow reenters the main passage flow is very important due to the dominant influence of the leakage flow on the aerodynamics of low aspect ratio turbines. The work presented in this paper investigates, both experimentally and numerically, possibilities for the control of shroud leakage flow by modifications to the exit shroud cavity. The processes through which the leakage flow affects the mainstream aerodynamics identified in the first part of this study were used to develop promising strategies for reducing the influence of shroud leakage flow. The experimental program of this study was conducted on a three-stage model air turbine, which was extensively supported by CFD analysis. Three different concepts for shroud leakage flow control in the exit cavity were analyzed and tested: (a) profiled exit cavity downstream end wall, (b) axial deflector, and (c) radial deflector concepts. Reductions in aerodynamic losses associated with shroud leakage were achieved by controlling the position and direction at which the leakage jet reenters the mainstream when it leaves the exit shroud cavity. Suggestions are made for an optimum shroud and cavity geometry.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of model turbine

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Figure 2

The stage geometry with open shroud cavities

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Figure 3

Computational domain (1.5 stage turbine) and grid details (every three nodes in span- and streamwise directions)

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Figure 4

Radial velocity distribution in the exit cavity for two different circumferential positions, close to (a) pressure side and (b) suction side (CFD )

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Figure 5

(a) Geometric details and (b) the radial velocity distribution in the case with the chamfered cavity downstream edge

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Figure 6

Cp0 contours downstream of Stator 3 in the case with chamfered cavity downstream edge (expt.)

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Figure 7

Yaw angle distribution downstream of Stator 3 in the case with chamfered cavity downstream edge (expt.)

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Figure 8

(a) Geometric details and (b) the radial velocity distribution in the case with the contoured cavity downstream end wall

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Figure 9

Radial velocity distribution at the interface between the exit cavity and the main passage in the case with profiled cavity downstream end wall (CFD )

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Figure 10

Cp0 contours downstream of Stator 3 in the case with contoured cavity downstream end wall (expt.)

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Figure 11

Yaw angle distribution downstream of Stator 3 in the case with contoured cavity downstream end wall (expt.)

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Figure 12

Absolute yaw angle downstream of the exit cavity in the case with contoured cavity downstream end wall (CFD )

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Figure 13

(a) Geometric details and (b) the radial velocity distribution in the case with straight axial deflector

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Figure 14

Cp0 contours downstream of Stator 3 in the case with straight axial deflector (expt.)

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Figure 15

Yaw angle distribution downstream of Stator 3 in the case with straight axial deflector (expt.)

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Figure 16

(a) Geometric details and (b) the radial velocity distribution in the case with inclined axial deflector

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Figure 17

Radial velocity distribution at the interface between the exit cavity and the main passage in the case with different axial deflector geometries (CFD )

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Figure 18

Absolute yaw angle downstream of the exit cavity in the case with different axial deflector geometries (CFD )

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Figure 19

Cp0 contours downstream of Stator 3 in the case with inclined axial deflector (expt.)

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Figure 20

Yaw angle distribution downstream of Stator 3 in the case with inclined axial deflector (expt.)

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Figure 21

(a) Geometric details and (b) the radial velocity distribution in the case with circular deflector

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Figure 22

(a) Geometric details, and (b) the radial velocity distribution in the case with Radial deflector A

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Figure 23

(a) Geometric details and (b) the radial velocity distribution in the case with Radial deflector B

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Figure 24

(a) Geometric details and (b) the radial velocity distribution in the case with Radial deflector C

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Figure 25

Entropy function downstream of the rotor for the (a) datum and (b) optimized shroud geometry (CFD )

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Figure 26

Absolute yaw angle downstream of the exit cavity in the case with (a) datum and (b) optimized cavity (CFD )

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Figure 27

Entropy function downstream of the stator for the (a) datum and (b) optimised shroud geometry (CFD )

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