Relationship Between Internal Flow and Fan Noise of Cross Flow Fan
Relationship Between Internal Flow and Fan Noise of Cross Flow Fan
Relationship Between Internal Flow and Fan Noise of Cross Flow Fan
Relationship between Internal Flow and Fan Noise of Cross Flow Fan
(Received 10 December 2009; received in revised form 28 April 2010; accepted 12 June 2010)
Abstract vortex and the accompanying flow around the vortex. The
The cross flow fan has an eccentrically located vortex inside effect of the tongue geometry on rotation noise level was
impeller. The vortex behavior has a large effect on the fan ascertained by flow measurements and numerical
performance and fan noise. Although investigations on the simulation of the internal flow.
internal flow of cross flow fan have been performed by
many researchers, quantitative relationship between the 2. Experimental Apparatus and Procedure
eccentrically located vortex and fan noise is not sufficiently 2.1 Measurements of fan performance and fan noise
made clear. In our previous study, we developed a noise Fig.1 shows the cross flow fan used in this study. The fan
reduction method of cross flow fan by using a step tongue had 27 blades with an outside pitch of 10 mm and 0.8 mm
and a skew tongue. Unfortunately, a detailed mechanism of blade thickness. The impeller had a 90 mm outside diameter
fan noise reduction is not known yet. In this paper the flow and was 127 mm in axial length. A 66.5 mm diameter hole
pattern and the fan noise of cross flow fan are was bored in one of the end plates to permit the insertion of
experimentally and numerically examined. the one-hole yaw meter. The tongue was flat and the casing
was composed of an arc joined to a flat duct. The
Key words experimental apparatus conforms to JIS B 8330 for the
Cross Flow Fan, Internal Flow, 3-D Numerical Simulation, configuration of air blowers, see Refs.[12, 13]. The
Fan Noise, Rotation Noise Level clearance between impeller and tongue was 3 mm in the
radial direction, and the clearance between leading edge of
1. Introduction casing and impeller was fixed at 11 mm. The flow rate was
In previous numerical simulation studies [1-3], cross flow controlled by changing the aperture ratio of the duct outlet.
fan performance and noise level were examined. In a very The pressure transducers, fan tachometer and the
recent analysis, Jeon and Cho [1] have shown through microphone were used to determine the fan performance
unsteady CFD and unsteady aeroacoustic pressure parameters and the noise level. The rotational speed of fan
calculations that “the interaction between the stabilizer and was maintained at 1400 min-1. A digital manometer was
rotating impeller generates tonal sound. Also, it is found used to record the static and total pressures in the duct. The
that the trailing edge of blade generates more acoustic noise measuring method was based on the noise level
pressure than the leading edge.” Meanwhile, Fukano et al. measurement standard JIS B 8346 for air blowers. The A-
[4-6] examined the effects of impeller, casing and tongue weighting fan noise was measured by a sound level meter,
configurations on the noise performance of cross flow fan. the data from which were input into a PC and processed via
Hayashi et al. [7] revealed that the fan noise could be the FFT contained in the LabVIEW8.0 software.
reduced by changing the blade shape. Lee et al. and Hyoung
[8, 9] conducted experiments on the effects of blade and
tongue configuration on noise reduction.
In our previous study, we developed a noise reduction
method of cross flow fan by using a step tongue and a skew
tongue [10, 11]. Unfortunately, a detailed mechanism of fan
noise reduction is not known yet.
In this study, the relationship between internal flow and
fan noise reduction of cross flow fan was experimentally
and numerically examined. The center of the eccentrically
located vortex was inferred from flow measurements. A
one-hole yaw meter [12, 13] was used to obtain the
pressure distributions along the inner and outer peripheries
of impeller. The behavior of the eccentrically located
vortex was estimated from the results of pressure
distributions.
A 3-D numerical analysis was carried out and was
compared with the experimental result. The position of
eccentrically located vortex was mainly influenced by air
flow rate. The rotation noise level was inferred to result
from the change in the position of the eccentrically located Fig.1 Experimental apparatus
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K. NISHIHARA, Y. NAKAHATA, C. W. KNISELY and M. IGUCHI
ψt=2pt/ρu22
inner and outer peripheries, respectively, vθ1 and vθ2 are the
(1) circumferential velocities on the inner and outer peripheries,
flow coefficient φ,
respectively. In addition, u1 and u2 are the rotational speeds
of impeller based on the inner and outer diameters,
φ=Q/DLu2
respectively. The above-mentioned one-hole yaw meter was
(2) traversed to measure vr1, vr2, vθ1 and vθ2.
w1=vr1/sinβ1 (4)
w2=vr2/sinβ2 (5)
tanβ1=vr1/(vθ1-u1)
Fig.3 Relative velocities on the inner and outer peripheries
(6)
Inlet
Side plate
Impeller Outlet
Measurement duct
y
z x
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Journal of JSEM, Vol.10, Special Issue (2010)
4. Results and Discussion of Experiments and 3-D As the rotation noise level is extremely lower than overall
Numerical Simulation noise level, as can be seen in Fig.7 (a), the turbulence noise
chain line drawn between φ= 0.3 and 0.7 is the results of 3- an essential role for φ =0.3. These results collectively
level are comparable. Accordingly, the rotation noise plays
D numerical simulation. The values of total pressure indicate that the rotation noise is significant in the low flow
agree with each other for φ= 0.3 to 0.5, while the two
coefficient,ψt , of experiment and 3-D numerical simulation rate regime, while the turbulence noise is dominant in the
high flow rate regime.
Fig.5 Relation between total pressure coefficient ψt and (a) φ=Max (high flow rate) (b) φ=0.3 (low flow rate)
total pressure efficiency ηt Fig.7 Spectral SPL
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K. NISHIHARA, Y. NAKAHATA, C. W. KNISELY and M. IGUCHI
the vortex center for φ= 0.3 separated far from the edge of
therefore would be the main noise source. On the other hand,
Edge of tongue
based on the 3-D numerical simulation are in good
agreement with the experimental ones in the two cases.
Definite difference cannot be seen between the results
shown in Figs.10 and 11. Consequently, it is difficult at
present to discuss the effects of the relative velocity vectors
on noise generation.
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Journal of JSEM, Vol.10, Special Issue (2010)
blade pitch above or below the datum. Tongues D, E, F and 5.2.2 Fan noise performance
in Fig.18. Fig.18 (a) shows the overall noise level for φ=φ
(step tongue D, skew tongue I) with that of flat tongue A in rotation noise level for the nine different tongues are shown
Fig.15. Meanwhile, Fig.16 shows a relatively significant
decrease in the SPL and K, especially for tongues D and I. max differs more than 17 dB from rotation noise level. At this
The SPL are reduced except for high flow rate (φ≥0.7). flow rate, turbulence noise (sometimes called the broad
Fig.18 (b) shows the noise data for a low flow rate of φ=
band noise [1, 8]) is the main noise source. Meanwhile,
Fig.15 Relation between total pressure coefficient ψt and Fig.17 Spectra SPL for tongue D and I (φ=0.3)
total pressure efficiency ηt for tongues A, D and I
(a) φ=φmax
Fig.18 Overall noise level and rotation noise level for nine
Fig.16 SPL and specific noise level K for tongues A, D and types of tongue
I
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K. NISHIHARA, Y. NAKAHATA, C. W. KNISELY and M. IGUCHI
http://ecim.co.kr/down/Aeroacoustic%20noise%20sou
rce%20of%20Air-
conditioner%20including%20CFF.PDF as downloaded
(2005).
[2] Yong J. M., Cho, Y. and Hyunsik, N.: Numerical
Prediction of the Cross-Flow Fan Performances and
Noise Characteristics by Unstructured Flow Solver
Algorithm, Proceedings of 4th KSME-JSME Fluids
Eng., (1998), 185-188.
[3] Yong, C. and Young, J. M.: Discrete Noise Prediction
of Variable Pitch Cross-Flow Fans by Unsteady
Navier-Stokes Computations, Trans, ASME J. Fluids
(b) φ=0.3
Eng., 125(2003), 543-550.
[4] Fukano, T. Hara, T. Yamashita, Y. Kinoshita, K. and
Nomiyama, S.: Reduction of Noise Generated by a
Fig.18 Overall noise level and rotation noise level for nine Cross Flow Fan (Part 1: The Effect of Geometries of a
types of tongue
Tongue and a Rotor) (in Japanese), Turbomachinery,
20-8(1992), 464-470.
6. Conclusions [5] Fukano, T. Hara, Y. Yamashita, Y. and Kinoshita, K.:
Experimental and numerical investigations were curried out Reduction of Noise Generated by a Cross Flow Fan
to reveal the relationship between the flow pattern and the
(Part 2: The Effect of the Clearance between a Tongue
fan noise of cross flow fan. The main findings obtained in and a Rotor) (in Japanese), Turbomachinery, 21-
this study can be summarized as follows:
6(1993), 350-357.
(1) The characteristics of internal flow inside impeller
[6] Fukano, T. Hara, Y. Yamashita, Y. and Kinoshita, K.:
obtained from 3-D numerical analysis are in good
Reduction of Noise Generated by a Cross Flow Fan
agreement with those experimentally measured under
(Part 3: The Effect of Scroll Shape) (in Japanese),
every experimental condition.
Turbomachinery, 21-8(1993), 466-472.
(2) The rotation noise is the main noise source in the low
[7] Hayashi, T., Kobayashi, Y., Nagamori, A. and Horino,
flow rate regime, while the turbulence noise is the main
T.: Low-Noise Design for Cross-Flow Fan Based on
noise source in the high flow rate regime. Change in the
Frequency Modulation (in Japanese), Trans. Jpn. Soc.
main noise source is closely associated with the shift of
Mech. Eng., 62C-601(1996), 3446-3451.
the center location of the eccentric vortex.
[8] Lee, D. S., Chen, P. H. and Miao, J. M.: Noise
(3) In the case that the rotation noise is the main noise
Reduction of a Cross-Flow Fan, J. Chin. Soc. Mech.
source, the alteration of tongue shapes is very effective
Eng., 20-3(1997), pp.265-273.
for reducing the noise level.
[9] Hyoung, M. K.: Discrete Frequency Noise Reduction
of the Cross-Flow Fan of the Split Type Room Air-
Nomenclature Conditioners Using the Skewed Stabilizers, JSME
D diameter of impeller, m
International Journal, 43-1(2000), 104-109.
K specific noise level, dB
[10] Nishihara, K., Knisely, C. W., Nakahata, Y., Kashima,
L impeller width, m
K. and Iguchi, M.: Study of Noise Reduction in Cross
pt total pressure, Pa
Flow Fans with Annular Bands, J. JSEM Special Issue,
ps static pressure, Pa
(2009), in press.
Q flow rate, m3/s
[11] Nakahata, Y., Knisely, C. W., Nishihara, K. and Iguchi,
SPL sound pressure level, dB
M.: Development of Noise Reduction Method and
u rotational velocity, m/s
Visualization Studies in Cross-Flow Fan, J. JSEM, 7-
x axial coordinate 4(2007), 349-354.
y vertical coordinate [12] Murata, S. and Nishihara, K.: An Experimental Study
z horizontal coordinate
φ
of Cross-Flow-Fan (1st Report, Effects of Housing
ρ density, kg/m3 Geometry on the Fan Performance) (in Japanese),
ψt
flow coefficient Trans. Jpn. Soc. Mech. Eng., 41-347(1975), 2062-
total pressure coefficient 2075.
[13] Murata, S. and Nishihara, K.: An Experimental Study
References of Cross-Flow-Fan (2nd Report, Fan Performance
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Noise Source of an Air-Conditioner Including Cross Mech. Eng., 41-347(1975), 2076-2089.
Flow Fan”,
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