Research Papers

Numerical and Experimental Study on the Tonal Noise Generation of a Radial Fan

[+] Author and Article Information
Manoochehr Darvish

Laboratory of Thermo and Fluid Dynamics,
Department of Mechanical Engineering,
University of Applied Sciences HTW Berlin,
Wilhelminenhofstr. 75A,
Berlin 12459, Germany
e-mail: darvish@htw-berlin.de

Stefan Frank

Laboratory of Thermo and Fluid Dynamics,
Department of Mechanical Engineering,
University of Applied Sciences HTW Berlin,
Wilhelminenhofstr. 75A,
Berlin 12459, Germany
e-mail: Stefan.Frank@htw-berlin.de

Christian Oliver Paschereit

Technical University of Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany
e-mail: oliver.paschereit@tu-berlin.de

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received April 6, 2015; final manuscript received April 23, 2015; published online May 27, 2015. Assoc. Editor: Ronald Bunker.

J. Turbomach 137(10), 101005 (May 27, 2015) (9 pages) Paper No: TURBO-15-1063; doi: 10.1115/1.4030498 History: Received April 06, 2015

The main focus of this work is on the geometrical modifications can be made to the fan wheel and to the volute tongue of a radial fan to reduce the tonal noise. The experimental measurements are performed by using the in-duct method in accordance with ISO 5136. In addition to the experimental measurements, CFD (computational fluid dynamics) and CAA (computational aeroacoustics) simulations are carried out to investigate the effects of different modifications on noise and performance of the fan. It is shown that by modifying the blade outlet angle, the tonal noise of the fan can be reduced without impairing its aerodynamic performance. Moreover, it is indicated that increasing the number of blades leads to a significant reduction in the tonal noise and also an improvement in the aerodynamic performance. However, this trend is only valid up to a certain number of blades, and a further increment might reduce the aerodynamic performance of the fan. Besides modifying the impeller geometry, new volute tongues are designed and tested on the rig. It is demonstrated that the shape of the volute tongue plays an important role in the tonal noise generation of the fan. Moreover, in order to find out whether or not it is possible to reduce the tonal noise level through a destructive phase-shift generation, stepped tongues are comprehensively investigated by means of numerical simulations and experimental measurements.

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Fig. 1

Geometrical dimensions and parameters of the fan (reference model) [8]

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Fig. 2

Schematic illustration of the experimental setup

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Fig. 3

Distribution of the slit-tube microphones in the measurement duct calculated according to DIN 5136

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Fig. 4

Unstructured mesh with 12.5 × 106 polyhedral cells

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Fig. 5

The noise radiated from the fan was predicted using the pressure monitors placed in the discharge of the fan as well as a FW–H monitor installed near the outlet

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Fig. 6

Influence of changing the number of blades on the shape of the velocity profile above the impeller (results from numerical simulations)

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Fig. 7

The effect of changing the number of blades on the distribution of the TKE above the impeller

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Fig. 8

Static efficiency versus flow rate of the fans with different number of impeller blades

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Fig. 9

Spectral noise analysis of the fans with different number of impeller blades; St = 1 corresponds to the blade passing frequency

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Fig. 10

Static efficiency versus flow rate of 38 blade impellers with different outlet angles

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Fig. 11

The effect of changing the blade outlet angle on the size of the flow separation between the impeller channels

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Fig. 12

Spectral noise analysis of the impellers with different blade outlet angles; St = 1 corresponds to the blade passing frequency

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Fig. 13

Transient surface data representing the pressure fluctuation and the SPL of different cutoff configurations at the blade passing frequency while the fan operates at its BEP [29]. (a) 0-10-16 (Reference), (b) HLHL-8.25-10-16, (c) LHLH-8.25-10-16, (d) HLHL-16.5-10-16, and (e) LHLH-16.5-10-16.

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Fig. 14

The pressure patterns (top) obtained from the monitors installed on the reference cutoff at the displayed positions (bottom). The curves are “in-phase” condition; the scalar shows pressure fluctuations [29].

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Fig. 15

Static efficiency versus flow rate of different cutoff models

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Fig. 16

The pressure patterns obtained from the monitors installed on the leading H and L segments of the HLHL tongues with 8.25 mm (top) and 16.5 mm (bottom) height difference

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Fig. 17

The pressure patterns obtained from the monitors installed on the leading L and H segments of the LHLH tongues with 8.25 mm (top) and 16.5 mm (bottom) height difference

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Fig. 18

Comparison between the experimental results of different cutoff arrangements. The plot shows the cumulative SPLs measured at four different flow rates. The inset at bottom focuses on the frequency band that includes the blade passing frequency.




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