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Research Papers: Flows in Complex Systems

A Parametric Study of Passive Flow Control for a Short, High Area Ratio 90deg Curved Diffuser

[+] Author and Article Information
T. P. Chong1

ISVR, University of Southampton, University Road, Southampton SO17 1BJ, UKt.p.chong@soton.ac.uk

P. F. Joseph, P. O. Davies

ISVR, University of Southampton, University Road, Southampton SO17 1BJ, UK

1

Corresponding author.

J. Fluids Eng 130(11), 111104 (Sep 23, 2008) (12 pages) doi:10.1115/1.2969447 History: Received September 21, 2007; Revised June 09, 2008; Published September 23, 2008

This paper represents the results of an experimental program with the aim of controlling the flow in a highly unstable 90deg curved diffuser. The diffuser, which is an integral part of an open jet wind tunnel at the University of Southampton, has the unique configuration of extreme shortness and high area ratio. In this study, several passive flow control devices such as vortex generators, woven wire mesh screens, honeycomb, and guide vanes were employed to control the three-dimensional diffusing flow in a scaled-down model. Although less successful for vortex generators, the other devices were found to improve significantly the uniformity of the flow distribution inside the curved diffuser and hence the exit flow. This study suggests that a cumulative pressure drop coefficient of at least 4.5 at the diffuser exit with at least three guide vanes is required to achieve adequate flow uniformity at the diffuser exit. These flow conditioning treatments were applied to the full-scale diffuser with exit dimensions of 1.3×1.3m2. Flow with comparable uniformity to the scale-model diffuser is obtained. This study provides valuable guidelines on the design of curved/straight diffusers with nonseparated flow and minimal pressure distortion at the exit.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

(a) A schematic depicting the parameters needed to describe a curved diffuser. (b) Location of the first appreciable stall as a function of Δϕ for circular-arc centerline curved diffusers (data tabulated from Ref. 3).

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Figure 2

Schematic of the experimental facility for the flow control study on the 90deg-curved diffuser model. Coordinate system for the diffuser exit flow is also shown. Insert diagram: Schematic of a typical guide vane profile. Guide vanes with different aspect ratios employed in this study were also shown in the table.

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Figure 3

Schematic showing the design of the 90deg-curved diffuser model. All dimensions are in millimeters.

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Figure 4

Schematics showing the parameters required to describe the (a) rectangular and (b) triangular-shaped vortex generators

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Figure 5

(a) Comparison of (—) theoretical and (●) measured Cp for the base line case (q=0, gv=0, vg=0). (b) and (c) Measured Cp0 and velocity contours for the base line case, respectively.

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Figure 6

Cp distributions for (—) base line, (△) (q=0, gv=0, vg=1), and (◻) (q=0, gv=0, vg=2) cases

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Figure 7

Velocity contour for the (q=0, gv=0, vg=2) case

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Figure 8

Cp distributions between (—) base line and (△) (q=0, gv=7, vg=0) cases

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Figure 9

(a) Measured Cp0 and (b) velocity contours for the (q=0, gv=7, vg=0) case

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Figure 10

Cp distributions between (—) base line and (△) (q=5.5, gv=0, vg=0) cases

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Figure 11

(a) Measured Cp0 and (b) velocity contours for the (q=5.5, gv=0, vg=0) case

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Figure 12

Cp distributions for (△) (q=3, gv=3, vg=0), (□) (q=3, gv=7, vg=0), (×) (q=5.5, gv=3, vg=0), (○) (q=5.5, gv=7, vg=0), and (—) base line cases

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Figure 13

Comparison of (q=3, gv=3, vg=0), (q=3, gv=7, vg=0), (q=5.5, gv=3, vg=0), (q=4.5, gv=7, vg=0), and (q=5.5, gv=7, vg=0) cases for (a1)–(a5) measured Cp0 and (b1)–(b5) velocity contours, respectively

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Figure 14

Comparison for turbulence intensity contours between (a) (q=3, gv=7, vg=0) and (b) (q=5.5, gv=7, vg=0) cases

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Figure 15

(a) Inner structure of the full-size 90deg-curved diffuser. (b) Curved diffuser installed inside the ISVR anechoic chamber.

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Figure 16

(a) Comparison of velocity deviations from the outer to the inner walls at Y=0.5 of the 90deg-curved diffuser exit for (○) treated scale model, (△) bare, untreated scale-model, and (◻) treated ful-size 90deg-curved diffusers. (b) Distributions of the exit velocity at different spanwise locations, y, from the outer to the inner walls of the full-size 90deg-curved diffuser.

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