Experimental Investigation of the Sound Emission of Skewed Axial Fans with Leading-Edge Serrations

Krömer, Florian; Czwielong, Felix; Becker, Stefan

doi:10.2514/1.j058134

Cited by 27 publications

(20 citation statements)

References 33 publications

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“…Some authors showed that a non-uniform distribution of the sweep angle in the radial sections, with a more accentuated sweep at the blade tip, can be beneficial in the behavior of axial fans (Wadia et al 1998;Corsini and Rispoli 2004;Masi and Lazzaretto 2017;Herold et al 2017;Krömer and Becker 2018;Krömer et al 2019).…”

Section: Circumferential Sweepmentioning

confidence: 99%

“…As a consequence, the forward circumferential sweep leads to a decrease in the unstable blade forces and, hence, to a reduction in the level of tonal peaks in the blade passage frequency and its harmonics. Fans with forward sweep weaken the tip vortex formation due to the modification in blade loading and thus they reduce the noise of the blade tip (Krömer et al 2019).…”

Section: Introductionmentioning

confidence: 99%

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Free and Non-Free Vortex Design for Axial Fans with Circumferential Sweep through CFD Techniques

2022

JAFM

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The sound generated by axial flow fans has become increasingly important in several industrial areas. These devices represent considerable noise sources that must be considered from the design stage. The scope of this research work is to present an axial fan design methodology based on the theory of the wing lift and to compare the aerodynamic and aeroacoustics behavior with the free vortex and the non-free vortex conditions. The effect of forward circumferential sweep on the rotor blades is analyzed in both conditions, which consists of a displacement in the tangential direction in the direction of rotor rotation. A cubic polynomial function is proposed for the construction of the blade geometry with circumferential sweep. It defines the center line of the blade and it is taken at 50% of the leading edge of each blade profile. The methodology for analyzing aeroacoustics behavior in fans is based on the integration of Computational Aeroacoustics and Computational Fluid Dynamics in order to analyze aerodynamic behavior, sound power level and sound pressure level at the preliminary design stage. It was verified that although both rotors present a similar aerodynamic behavior (the NFV rotor has a slightly lower performance), according to the analysis of local sound sources, the NFV rotor presents a slight decrease in the sound sources. It was also verified that the NFV rotor presents 2.2 dB less in sound pressure level than the FV rotor.

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Section: Circumferential Sweepmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Free and Non-Free Vortex Design for Axial Fans with Circumferential Sweep through CFD Techniques

2022

JAFM

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“…However, leading-edge treatment approaches to reduce turbulence interaction noise also exist for axial fans, including leading-edge serrations [31][32][33][34][35][36] and porous materials [37][38][39]. In addition, modifications of the shape of the blades in the form of sweeping or skewing are known as effective means for noise reduction [3,[40][41][42][43][44].…”

Section: Introductionmentioning

confidence: 99%

Permeable Leading Edges for Airfoil and Fan Noise Reduction in Disturbed Inflow

Ocker

Geyer

Czwielong³

et al. 2021

AIAA Journal

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A detailed experimental study on the aerodynamic performance and noise emission of airfoils and fan blades with permeable leading edges under disturbed inflow conditions was performed. The airfoils and fan blades with permeable leading edges were made of an aluminum alloy using a powder bed fusion-based additive manufacturing process. In a first step, a wind-tunnel study was carried out. This consisted of detailed aerodynamic and aeroacoustic measurements on 16 airfoils with different permeable leading-edge designs that were performed for various flow speeds and geometric angles of attack. Based on the results from that study, unskewed fan blades with four different permeable leading-edge designs were manufactured in a second step. With the aim of reducing turbulence interaction noise of axial fans, the fans were examined with regard to their aerodynamic and acoustic properties under grid-generated turbulent inflow conditions. In a third step, a possible transfer of the observed noise emission from airfoils with permeable leading edge to that of fan blades was investigated. It was found that a notable broadband noise reduction can be transferred from airfoil applications to the sound spectra of axial fans. At the same time, the porous modifications can reduce the aerodynamic performance, and hence the fan efficiency.

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“…This is due to the effect that the heat exchanger interferes with the flow field of the axial fan, thus amplifying the sound generation mechanisms at the axial fan. To counteract these increased sound emissions, either the flow guidance of the heat exchanger could be optimized, the axial fan could be designed for specific inflow turbulence, sound-reducing modifications to the fan such as serrations, slits or porous materials could be used, or classic silencers could be connected upstream or downstream of the heat exchanger module [3][4][5][6]. However, these noise reduction measures have so far only been used to a limited extent in industrial applications.…”

Section: Introductionmentioning

confidence: 99%

Sound reduction in heat exchanger modules by integrating plate absorbers with sub-millimeter openings

2021

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In air conditioning systems heat exchangers are frequently installed upstream of ventilators. These modules are part of the daily life of humans and should therefore create an environment that is as quiet as possible. The heat exchanger generates increased turbulence, which leads to increased sound emissions of the ventilator. Due to installation space limitations, it is not possible to connect silencers to the heat exchanger module. A novel concept is presented, which allows to reduce the sound emissions of heat exchanger due to plate absorbers without the need of additional installation room. The plates contain sub-millimeter openings. They are integrated into the heat exchanger housing together with back volumes. This arrangement guarantees compactness and generates no additional flow resistance. The emitted sound could be reduced by up to 2.9 dB in the partial load range. The main advantages of the concept presented are individual adjustment, cost-effective design and simple installation.

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Experimental Investigation of the Sound Emission of Skewed Axial Fans with Leading-Edge Serrations

Cited by 27 publications

References 33 publications

Free and Non-Free Vortex Design for Axial Fans with Circumferential Sweep through CFD Techniques

Free and Non-Free Vortex Design for Axial Fans with Circumferential Sweep through CFD Techniques

Permeable Leading Edges for Airfoil and Fan Noise Reduction in Disturbed Inflow

Sound reduction in heat exchanger modules by integrating plate absorbers with sub-millimeter openings

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