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Research Papers

Transition on the T106 LP Turbine Blade in the Presence of Moving Upstream Wakes and Downstream Potential Fields

[+] Author and Article Information
Maciej M. Opoka1

Whittle Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 ODY, UKmaciej.opoka@rolls-royce.com

Howard P. Hodson

Whittle Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 ODY, UK

1

Present address: Rolls Royce Deutschland, Dahlewitz, Germany.

J. Turbomach 130(4), 041017 (Aug 04, 2008) (12 pages) doi:10.1115/1.2812415 History: Revised July 02, 2007; Received July 11, 2007; Published August 04, 2008

Boundary layer measurements were performed on a cascade of the T106 high lift low-pressure (LP) turbine blades that was subjected to upstream wakes and a moving downstream potential field. Tests were carried out at a low level of inlet freestream turbulence (0.5%) and at a higher (4.0%). It is found that perturbations in the freestream due to both disturbances are superposed on each other. This affects the magnitude of the velocity perturbations at the edge of the boundary layer under the wakes as well as the fluctuations in the edge velocity between the wakes. Furthermore, the fluctuations in the adverse pressure gradient on the suction surface depend on the relative phase of the upstream and downstream disturbances, providing an additional stimulus for clocking studies. Time-mean momentum thickness values calculated from laser Doppler anemometry (LDA) traverses performed near the suction surface trailing edge are used to identify the optimum relative phase angle of the combined interaction. Unsteady suction surface pressures, quasiwall shear stress and LDA data illustrate the resulting multimode process of transition, which is responsible for the observed clocking effects. The optimum relative phase angle of the upstream wake and the downstream potential field can produce 0.25% of efficiency improvement through the reduction of the suction surface boundary layer loss. This reduction is mainly related to the calmed region and the laminar flow benefits that can be more effectively utilized than when only the upstream wakes are present. During the remaining parts of the cycle, the features that are usually associated with the wake and the potential field effects are still present.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

T106A LP turbine bar passing rig

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Figure 2

T106A cascade, with upstream and downstream bars shown at time t∕τ0=0.0 and relative phase angle ϕ-ϕ0=0.0deg, 60.0deg, 120.0deg, 168.0deg, 217.5deg, 300.0deg

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Figure 3

Nondimensional ensemble averaged velocity at the boundary layer edge due to separate and combined effects Re2is=1.6×105, Fred=0.46, and Tu1=0.5%, s∕S0=0.96, ϕ-ϕ0=0.0deg

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Figure 4

Influence of the relative phase angle (ϕ-ϕ0) of combined interactions illustrated with nondimensional ensemble averaged velocity at the boundary layer edge. Re2is=1.6×105, Fred=0.46, and Tu1=0.5%, s∕S0=0.96, ϕ-ϕ0=0.0deg, 60.0deg, 120.0deg, 168.0deg, 217.5deg, 300.0deg

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Figure 5

Effect of Clocking—Time mean of momentum thickness, at trailing edge location at Tu1=0.5% and 4.0%, Re2is=1.6×105, Fred=0.46 at surface distance of s∕S0=0.96, steady flow, wake-only, potential field-only, and combined interaction at ϕ-ϕ0=0.0deg, 60.0deg, 120.0deg, 168.0deg, 217.5deg, 300.0deg

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Figure 6

Effect of Clocking—Surface pressure coefficient measured at ϕ-ϕ0=120.0deg and ϕ-ϕ0=300.0deg for both Tu1=0.5% and Tu1=4.0%, Re2is=1.6×105, Fred=0.46

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Figure 7

Ensemble averaged distribution of surface pressure coefficient Cp,2is, measured at Re2is=1.6×105, Fred=0.46, Tu1=0.5%, and ϕ-ϕ0=120.0deg

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Figure 8

Ensemble averaged distribution of surface pressure coefficient Cp,2is, measured at Re2is=1.6×105, Fred=0.46, Tu1=0.5%, and ϕ-ϕ0=300.0deg

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Figure 9

Ensemble averaged of suction surface pressure coefficient Cp,2is at five time instants within one period of the combined interaction. Data measured at Re2is=1.6×105, Fred=0.46, Tu1=0.5% and 4.0% and ϕ-ϕ0=120.0deg and 300.0deg

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Figure 10

Combined Interaction—raw hot film signals, Re2is=1.6×105, Fred=0.46, Tu1=0.5%, ϕ-ϕ0=120.0deg—first minimum of momentum loss, ϕ-ϕ0=300deg—second minimum of momentum loss

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Figure 11

Combined Interaction—raw hot film signals, Re2is=1.6×105, Fred=0.46, and Tu1=4.0%, ϕ-ϕ0=120deg—minimum of momentum loss, ϕ-ϕ0=300deg—minimum of momentum loss

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Figure 12

Traces of ensemble averaged momentum thickness measured at s∕S0=0.96, Re2is=1.6×105, Fred=0.46, Tu1=0.5%, ϕ-ϕ0=120.0deg, ϕ-ϕ0=300.0deg, and single wake

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Figure 13

Traces of ensemble averaged momentum thickness measured at s∕S0=0.96, Re2is=1.6×105, Fred=0.46, Tu1=4.0%, ϕ-ϕ0=120.0deg, ϕ-ϕ0=300.0deg, and single wake

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