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Research Papers: Gas Turbines: Turbomachinery

Investigation of Tabs in Short Annular Diffusers With Swirling Flow

[+] Author and Article Information
D. J. Cerantola

Department of Mechanical and
Materials Engineering,
Queen's University,
Kingston, ON K7L 3N6, Canada
e-mail: david.cerantola@queensu.ca

A. M. Birk

Department of Mechanical and
Materials Engineering,
Queen's University,
Kingston, ON K7L 3N6, Canada
e-mail: birk@me.queensu.ca

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 26, 2014; final manuscript received January 24, 2015; published online February 18, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(9), 092601 (Sep 01, 2015) (8 pages) Paper No: GTP-14-1639; doi: 10.1115/1.4029695 History: Received November 26, 2014; Revised January 24, 2015; Online February 18, 2015

Square tabs were placed on the base of an ellipsoidal center-body (CB) in short annular diffusers. Tests were conducted in subsonic swirling flow with an inlet Reynolds number of 1 × 105. The tabs, with a projected height equivalent to the boundary layer thickness, reduced the outlet distortion and incurred a pressure penalty in the three smaller diffusers whose designs were not expected to stall. The largest area ratio (AR = 6.18) diffuser improved back pressure coefficient 4.6% with four tabs that blocked 4.7% of the inlet cross section over its bare diffuser but was 42% lower than that obtained by the AR = 2.73 diffuser with no tabs. Computational fluid dynamics (CFD) was useful for capturing relevant flow features that corroborated with experimental data and literature. Tabs oriented normal to the diffuser axis were less effective at influencing the flow as swirl angle increased but similar elongated wakes oriented with the flow direction were observed at all simulated swirl angles. The CFD either predicted equivalent performance due to the over-prediction associated with diffusion equaling the under-prediction associated with vorticity or over-predicted performance.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Annular diffuser cutaway

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Fig. 2

Test section schematic depicting instrumentation locations. Section  = three-hole probe traverse at annulus outlet (x = −1.05Do) and section  = three-hole probe traverse at annular diffuser inlet (x = −0.23Do). Squares denote wall pressure taps. At least two instruments were placed at each axial location.

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Fig. 3

Manufactured geometry components (symmetry plane shown)

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Fig. 4

Symmetry plane computational domain and boundary conditions. Cross sections:  = annulus outlet,  = annular diffuser inlet (x = −0.23Do),  = diffuser outlet.

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Fig. 5

AR = 2.73 diffuser with four tabs and St = 0.7 swirl predicted pressure planes and streamlines

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Fig. 6

AR = 2.73 diffuser with four tabs and St = 0.7 swirl axial velocity contours and velocity vectors. (a) x = 0, (b) x = 0.13Do, (c) x = 0.26Do, (d) x = 0.39Do, (e) x = 0.52Do, (f) x = 1.00Do.

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Fig. 7

AR = 2.73 diffuser with four tabs and St = 0.7 swirl predicted axial vorticity contours. See Fig. 6 for plane locations.

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Fig. 8

AR = 2.73 diffuser with four tabs and St = 0.7 swirl predicted azimuthal vorticity contours. See Fig. 6 for plane locations.

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Fig. 9

AR = 2.73 diffuser with four tabs and St = 0.7 swirl predicted turbulence intensity contours. See Fig. 6 for plane locations.

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Fig. 10

Configurations with four tabs and St = 0.7 swirl wall pressure distributions. CB data (solid symbols) on left axis and OW data (hollow symbols) on right axis. CFD nondimensionalized by the experimental 〈qt,exp〉. CFD results extracted along θ = 0 deg and θ = 45 deg planes. Experimental CB taps located at θ = 0 deg and OW taps at θ = 45 deg. (a) AR = 1.61 diffuser, (b) AR = 1.91 diffuser, (c) AR = 2.73 diffuser, and (d) AR = 6.18 diffuser.

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Fig. 11

AR = 1.91 diffuser with four tabs and St = 0.7 swirl outlet contours. CFD results plotted on top two quadrants and experiment on bottom two quadrants. Total pressure contours on left quadrants and axial vorticity contours on right quadrants.

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Fig. 12

AR = 2.73 diffuser with four tabs and St = 0.7 swirl outlet contours. See Fig. 11 for quadrant identifiers.

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Fig. 13

AR = 6.18 diffuser with four tabs and St = 0.7 swirl outlet contours. See Fig. 11 for quadrant identifiers.

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Fig. 14

Influence of swirl on performance with four tabs. CFD: solid lines = 0 tabs, dashed lines = 4 tabs. Exp: filled circles with error bars = 0 tabs, hollow circles = 4 tabs. (a) Back pressure and (b) outlet velocity uniformity.

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