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TECHNICAL PAPERS

Secondary Flows and Loss Caused by Blade Row Interaction in a Turbine Stage

[+] Author and Article Information
Graham Pullan

Whittle Laboratory,  University of Cambridge, Cambridge CB3 0DY, UKgp10006@eng.cam.ac.uk

J. Turbomach 128(3), 484-491 (Mar 01, 2004) (8 pages) doi:10.1115/1.2182001 History: Received October 01, 2003; Revised March 01, 2004

A study of the three-dimensional stator-rotor interaction in a turbine stage is presented. Experimental data reveal vortices downstream of the rotor which are stationary in the absolute frame—indicating that they are caused by the stator exit flowfield. Evidence of the rotor hub passage vortices is seen, but additional vortical structures away from the endwalls, which would not be present if the rotor were tested in isolation, are also identified. An unsteady computation of the rotor row is performed using the measured stator exit flowfield as the inlet boundary condition. The strength and location of the vortices at rotor exit are predicted. A formation mechanism is proposed whereby stator wake fluid with steep spanwise gradients of absolute total pressure is responsible for all but one of the rotor exit vortices. This mechanism is then verified computationally using a passive-scalar tracking technique. The predicted loss generation through the rotor row is then presented and a comparison made with a steady calculation where the inlet flow has been mixed out to pitchwise uniformity. The loss produced in the steady simulation, even allowing for the mixing loss at inlet, is 10% less than that produced in the unsteady simulation. This difference highlights the importance of the time-accurate calculation as a tool of the turbomachine designer.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 5

Measured stator exit stagnation pressure (p01̿−p0)/ρUmid2

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Figure 6

Measured time-averaged rotor exit relative yaw angle (degrees)

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Figure 4

Measured stator exit meridional yaw angle (degrees)

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Figure 3

CFD mesh, circumferential view (every second node shown)

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Figure 2

CFD mesh, meridional view (every second node shown)

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Figure 1

Meridional view of research turbine, showing traverse planes

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Figure 7

Measured time-averaged rotor exit absolute yaw angle (degrees)

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Figure 8

Predicted stator exit meridional yaw angle (degrees)

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Figure 9

Predicted stator exit stagnation pressure (p01̿−p0)/ρUmid2

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Figure 10

Calculated time-averaged rotor exit absolute yaw angle (degrees)—stage simulation

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Figure 11

Calculated time-averaged rotor exit absolute yaw angle (degrees)—rotor only simulation

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Figure 12

Measured and predicted time-averaged (pitchwise averaged) rotor exit absolute yaw angle

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Figure 13

Coordinate system definition

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Figure 14

Schematic of vortex formation mechanism

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Figure 15

Nondimensional component of absolute vorticity in η direction, stator exit, ωη∗

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Figure 16

Time-averaged passive scalar contours at rotor exit

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Figure 17

Generation of loss through the rotor-only computational domain

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Figure 18

Schematic of stator wake convection through rotor row

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