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Research Papers

Influence of the Sweep Stacking on the Performance of an Axial Fan

[+] Author and Article Information
Ayhan Nazmi Ilikan

Faculty of Mechanical Engineering,
ITU,
Inonu Cad. No. 65,
Gumussuyu/Beyoglu 34437, Istanbul, Turkey
e-mail: ilikana@itu.edu.tr

Erkan Ayder

Faculty of Mechanical Engineering,
ITU,
Inonu Cad. No. 65,
Gumussuyu/Beyoglu 34437, Istanbul, Turkey
e-mail: aydere@itu.edu.tr

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received November 22, 2013; final manuscript received October 6, 2014; published online December 11, 2014. Assoc. Editor: Michael Hathaway.

J. Turbomach 137(6), 061004 (Jun 01, 2015) (13 pages) Paper No: TURBO-13-1272; doi: 10.1115/1.4028767 History: Received November 22, 2013; Revised October 06, 2014; Online December 11, 2014

In modern turbomachinery blade design, nonradial stacking of the profiles is often assumed to be one of the ways to improve the performance of a machine. Instead of stacking the profiles radially, the stacking line is changed by several modifications such as sweep, dihedral, lean, or a combination of these. Nonradial stacking influences secondary flows that have effects on the aerodynamic parameters such as efficiency, pressure rise, blade loading, and stall margin. However, many of the studies in literature are limited by the comparison of two or three cases. This situation leads to conflicting results because a modification may cause a positive effect in one study while in another one, the same modification may have a negative effect. In this study, a modified free vortex axial fan (named as base fan (BF) for this study) is designed first and the profiles of the blades are stacked radially by joining the centroids of the profiles. Second, 45 deg, 30 deg forward sweep (FS) and backward sweep (BS) modifications are applied. The effects of these modifications on aerodynamic performance of the fans are investigated by means of numerical calculations. The results show that FS and BS do not significantly affect the overall performance of the fan at the design flowrate in spite of the occurring modifications of the local blade pressure distribution. However, at low flowrates, FS and BS have positive and negative effects on the fan performance, respectively.

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References

Figures

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Fig. 1

Nonradial stacking definitions [1]

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Fig. 2

The spanwise variations of the aimed (a) local total pressure rise coefficient, (b) absolute flow angle, and (c) nondimensionalized axial velocity at the design flowrate of the BF

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Fig. 3

The photograph of the BF inside the channel

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Fig. 4

Solid models of the base and swept fans

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Fig. 5

Meridional views of the base and swept fans

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Fig. 6

Computational domain

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Fig. 7

Comparison of the spanwise (a) total pressure distribution at the exit of the fan and (b) total pressure rise coefficient distribution for different mesh densities

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Fig. 8

Structured grid around the blade

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Fig. 11

Comparison of the calculated and measured BF total pressure rise coefficient characteristics

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Fig. 12

The validation of the CFD results at the design flowrate of the BF: (a) local total pressure rise coefficient, (b) absolute flow angle, and (c) nondimensionalized axial velocity

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Fig. 13

Performance characteristics of the forward (a) and backward (b) swept fan rotors (CFD calculations)

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Fig. 14

(a) Inlet axial velocity, (b) inlet radial velocity, and (c) nondimensional inlet total pressure profiles at design flowrate

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Fig. 15

Meridional velocity vectors at low flowrate: (a) base, (b) 45 deg FS, and (c) 45 deg BS

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Fig. 16

LE and tip vortices

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Fig. 17

Blade pressure distribution at design flowrate (at 0.1 of the span-close to hub)

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Fig. 18

Blade pressure distribution at design flowrate (at 0.9 of the span-close to tip)

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Fig. 19

Blade pressure distribution at design flowrate (at midspan)

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Fig. 20

Total pressure rise (design flowrate)

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Fig. 21

Total pressure rise (low flowrate)

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Fig. 22

Total pressure rise (high flowrate, Φd = 0.38)

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Fig. 23

Surface streamlines at the design flowrate: (a) base S.S., (b) FS45 S.S., (c) BS45 S.S., (d) base P.S., (e) FS45 P.S., and (f) BS45 P.S.

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Fig. 24

Velocity vectors at the tip gap region for design flowrate: (a) BF, (b) FS45, and (c) BS45

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