Experimental and numerical investigations of the tip leakage flow of axial fans with circumferential skewed blades under off-design conditions

Abstract

Experimental and numerical investigations of tip leakage flow of circumferential skewed axial fans were conducted under off-design conditions. Two circumferential skewed fans, with the blade skew angles of 8.3° forward and backward, respectively, and a base fan were investigated in this study. Aerodynamic and aeroacoustic performances were measured. The Navier—Stokes flow simulations were validated experimentally and the key analysis of tip leakage flow was based on computational fluid dynamics results. The simulations show that with a decrease in flowrate, the start of the tip leakage vortex moves towards the leading edge in the chordwise direction and towards the hub in the spanwise direction. These movements are less significant for the forward-skewed blade than for the backward-skewed blade. The strength of the tip leakage vortex decreases along the vortex line. The vortex strength for the forward-skew blade is significantly less than that for the backward-skewed blade. The aeroacoustic source intensity in the tip clearance region is reduced by employing circumferential skewed blades and changes with a change in flowrate in the same manner as the measured sound pressure level. The forward-skewed blade is found to be effective in eliminating noise sources in the tip clearance region and in controlling tip leakage flow to expand the stall-free operation range under off-design conditions.

Keywords

axial flow fan skewed blade tip leakage flow off-design condition aeroacoustic source

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References

Adamczyk

J. J.

Celestina

M. L.

Greitzer

E. M.

, ‘The role of tip clearance in high-speed fan stall’ Trans. ASME, J. Turbomach. 115 (1993): 28–38.

Mailach

Lehmann

Vogeler

, ‘Rotating instabilities in an axial compressor originating from the fluctuating blade tip vortex’ Trans. ASME, J. Turbomach. 123 (2001): 453–463.

Inoue

Kuroumaru

Yoshida

Minami

Yamada

Furukawa

, ‘Effect of tip clearance on stall evolution process in a low-speed axial compressor stage’ In ASME, International Gas Turbine Institute, Vienna, Austria, 2004, pp. 385–394, paper no. GT2004-53354.

X. J.

Liu

B. J.

Jiang

H. K.

, ‘Characteristics of the tip leakage vortex in a low-speed axial compressor’ AIAA J. 45 4 (2007): 870–878.

Lakshminarayana

Pandya

, ‘Tip clearance flow in a compressor blade passage at design and off-design conditions’ Trans. ASME, J. Eng. Gas Turbines Power 106 3 (1984): 570–577.

Lakshminarayana

Zaccaria

Marathe

, ‘The structure of tip clearance flow in axial flow compressor’ Trans. ASME, J. Turbomach. 117 (1995): 336–347.

Tallman

Lakshminarayana

, ‘Numerical simulation of tip leakage flows in axial flow turbines, with emphasis on flow physics. Part I: Effect of tip clearance height’ Trans. ASME, J. Turbomach. 123 2 (2001): 314–323.

Murthy

K. N. S.

Lakshminarayana

, ‘Laser Doppler velocimeter measurement in the tip region of a compressor blade’ AIAA J. 24 (1986): 807–814.

Jang

C. M.

Furukawa

Inoue

, ‘Analysis of vortical flow field in a propeller fan by LDV measurements and LES. Part I: Three-dimensional vortical flow structures’ Trans. ASME, J. Fluids Eng. 123 (2001): 748–754.

10.

Jang

C. M.

Fukano

Furukawa

, ‘Effects of the tip clearance on vortical flow and its relation to noise in an axial flow fan’ JSME Int. J. B 46 3 (2003): 356–365.

11.

Jang

C. M.

Sato

Fukano

, ‘Experimental analysis on tip leakage and wake flow in an axial flow fan according to flow rates’ Trans. ASME, J. Fluids Eng. 127 2 (2005): 322–329.

12.

Kameier

Neise

, ‘Experimental study of tip clearance losses and noise in axial turbomachines and their reduction’ Trans. ASME, J. Turbomach. 119 (1997): 460–471.

13.

Fukano

Jang

C. M.

, ‘Tip clearance noise of axial flow fans operating at design and off-design condition’ J. Sound Vibr. 275 (2004): 1027–1050.

14.

Zhu

X. C.

Lin

W. L.

Z. H.

, ‘Experimental and numerical investigation of the flow field in the tip region of an axial ventilation fan’ Trans. ASME, J. Fluids Eng. 127 (2005): 299–307.

15.

Beiler

M. G.

Carolus

T. H.

, ‘Computation and measurement of the flow in axial flow fans with skewed blades’ Trans. ASME, J. Turbomach. 121 1 (1999): 59–66.

16.

Vad

Kwedikha

A. R. A.

Jaberg

, ‘Effects of blade sweep on the performance characteristics of axial flow turbomachinery rotors’ Proc. IMechE, Part A: J. Power and Energy 220 A7 (2006): 737–749 DOI: 10.1243/09576509JPE249.

17.

Vad

, ‘Aerodynamic effects of blade sweep and skew in low-speed axial flow blades at the design flow’ Proc. IMechE, Part A: J. Power and Energy 222 A1 (2008): 69–85 DOI: 10.1243/09576509JPE471.

18.

Ouyang

Z. H.

, ‘Experimental study on aerodynamic and aero-acoustic performance of low pressure axial flow fan with circumferential skewed blades’ J. Aerosp. Power 21 4 (2006): 668–674.

19.

Corsini

Rispoli

, ‘Using sweep to extend the stall-free operational range in axial fan rotors’ Proc. IMechE, Part A: J. Power and Energy 218 A3 (2004): 129–139 DOI: 10.1243/095765004323049869.

20.

Lee

G. H.

Baek

J. H.

Myung

H. J.

, ‘Structure of tip leakage flow in a forward-swept axial-flow fan’ Flow, Turbul. Combust. 70 1–4 (2003): 241–265.

21.

Lee

G. H.

Baek

J. H.

Myung

H. J.

, ‘Effect of blade loading on the structure of tip leakage flow in a forward-swept axial-flow fan’ HVAC&R Res. J. 11 1 (2005): 95–117.

22.

Ouyang

Z. H.

, ‘Computational and experimental study on tip leakage vortex of circumferential skewed blades’ Chin. J. Mech. Eng. 20 2 (2007): 579–586.

23.

NUMECA International Inc. , FINETM Numeca's flow integrated environment. User manual, Version 6.2 (2004) (NUMECA International Inc., Brussels, Belgium).

24.

Spalart

P. R.

Allmaras

S. R.

, ‘One-equation turbulence model for aerodynamic flows’ Rech. Aerosp. 1 (1994): 5–21.

25.

Gummer

Goller

M. V.

Swoboda

, ‘Numerical Investigation of end wall boundary layer removal on highly loaded axial compressor blade rows’ Trans. ASME, J. Turbomach. 130 1 2008: 011015.

26.

Haimes

Kenwright

, ‘On the velocity gradient tensor and fluid feature extraction’ In Proceedings of the 14th AIAA Computational Fluid Dynamics Conference, 1999, paper 99-3288.

27.

Sujuki

Haimes

, ‘Identification of swirling flow in 3-D vector fields’ In Proceedings of the 12th AIAA Computational Fluid Dynamics Conference, 1995, paper 95-1715.

28.

Blake

W. K.

, Mechanics of flow-induced sound and vibration (1986) (Academic Press, New York).