Noise Of Axial Flow Fan Research Articles

Effect of tip winglet position on tip flow and noise of axial flow fan

In order to investigate the impact of blade tip winglet position on the internal flow and noise characteristics of axial flow fans,three different blade tip winglets,namely the TSW blade, the SSW blade, and the PSW blade,were hereby proposed. The accuracy of the simulation model was verified through experiments, and the circumferential internal flow characteristics and noise characteristics of these different blades were studied by numerical simulation using the blade tip partition method. The calculation results indicated the high-level efficiency of TSW, SSW and PSW blades in reducing the blade tip leakage flow in Z1 and Z2 regions and suppressing its circumferential propagation in the Z3 region. Besides, it was found that SSW blade and PSW blade had larger total pressure loss relative to Ori blade, and that TSW had higher total pressure difference at low blade height. Additionally TSW blades performed the best in improving the blade tip blockage,while TSW, SSW and PSW blades effectively reduced the leakage flow against the main stream, and blade tip winglet blades could effectively improve the fan discrete noise, SSW had the most significant noise reduction effect in the total sound pressure level, and in the overall blade,Z1, Z2 and Z3 were reduced by 2.16 dB,1.68 dB,2.24 dB and 3.74 dB.

Numerical and experimental investigation into effects of winglet shape on flow and noise performances of axial-flow fans for outdoor unit of air conditioner

In this study, the effects of winglet shape on the flow performance, efficiency, and aerodynamic noise of axial-flow fans, used as cooling fans in an outdoor unit of split-type air-conditioners, are numerically and experimentally investigated. Especially, a focus is placed on the coherent flow structures of the tip and leakage vortices: the former is generated from the fan blade tip near the leading edge, and the latter forms in the gap between the blade tip and the shroud. Two types of axial-flow fans are considered: one is with a blade-tip winglet, and the other is without the blade-tip winglet. The flow fields around the fans are simulated by numerically solving the three-dimensional unsteady incompressible RANS equations, and the radiated acoustic pressure is predicted using the Ffowcs-Williams and Hawkings equation. The validity of the numerical methods is confirmed through the predicted results with the measured ones. The flow field characteristics driven by the fans with and without the winglet are analyzed by comparing the detailed structure of the tip and leakage vortices in the gap flow region. In addition, the flow performance, efficiency, and sound pressure of the axial fans are characterized in association with the vortex structures. These results reveal that the winglet shape in the gap flow region has an adverse effect on the flow and acoustic performances of axial-flow fans by increasing the gap-vortex strength.

Study on aerodynamic noise of axial flow fan in ship signal cabinet

In order to study the aerodynamic noise characteristics of axial flow fan in the ship signal cabinet, the aerodynamic noise theory analysis and experimental research were carried out. By comparing and analyzing the vibration and noise spectrum of cabinet, it was determined that the noise of cabinet mainly came from the aerodynamic noise of axial flow fan in the cooling unit of rotating cage. The noise control of cabinet was studied by using the optimal design of the fan installation structure and the application of sound-absorbing cotton. The results show that the noise of fan was discrete noise. The noise increased 2.91 dB(A) when the net was installed in the fan inlet, meanwhile, the energy ratio of high-frequency noise (6000 to 14000 Hz) increased significantly. The sound was sharp. The noise of fan became smaller with the decrease of speed. The peak frequencies of fan noise spectrum were the multiple frequency of fundamental frequency and shaft frequency at different speeds. The sound pressure level was the largest at the fundamental frequency. That is, the noise of fan came from its blades. The noise reduction was 4.24 dB(A) by applying the sound-absorbing cotton on the inner wall of cabinet. The effects of noise reduction were obvious in the 200 to 2000 Hz range. The research results can provide theoretical and experimental support for the optimal design of ship signal cabinet.

Research and optimal design of an energy efficient axial fan

Ventilator, as a fluid machine, is widely used in many areas of national life, he has high efficiency, high flow, small volume and low pressure, etc., in daily life, mining and metallurgical industry and other fields have a wide range of applications. In this regard, efficiency and noise are two important indicators of fans, so for the existing fans, there is a need for a design that optimises the efficiency and noise of axial flow fans.

Effect of porous casing on small axial-flow fan noise

A novel casing treatment is studied to suppress the tip leakage vortex and postpone stall inception, leading to significant noise reduction. The new casing is made by open-cell metal foam, and its effect on both aerodynamic and acoustic performance of an axial-flow fan is investigated experimentally. As much as 10 dBA noise reduction is achieved, in the otherwise stalled flow condition. The mechanism is qualitatively analyzed by computational fluid dynamic simulations for three-dimensional, transient flow. It is found that, with the porous casing, the strength of tip leakage vortex decreases mainly because of the suppression of the pressure difference between the pressure side and suction side of the blade and the flow momentum transport at fluid-porous interface. By experimenting with different casing surfaces, the roughness of the porous casing is found not to be responsible for the delay of stall. Moreover, direct sound absorption by the porous casing is found to be negligible due to the limited volume of metal foam. The working mechanism is thus identified as purely aerodynamic.

Azimuthal Mode Experiment of Aerodynamic Noise of Axial Flow Fan for Electronic Device Heat Dissipation

Azimuthal Mode Experiment of Aerodynamic Noise of Axial Flow Fan for Electronic Device Heat Dissipation

窗式空调轴流风扇气动噪声研究

窗式空调轴流风扇气动噪声研究

Numerical simulation and experimental research on the aerodynamic performance of large marine axial flow fan with a perforated blade

In this study, some of the optimal parameters for a new-style marine axial flow fan are defined by using numerical simulation and experimental tests with a large marine axial flow fan, based on the analysis of the blade perforation’s influences on its internal flow field and aerodynamic noise characteristics. Test result shows that the noise reduction for the axial flow fan with perforated blade is about 3 dB when the blade perforation diameter D is 10 mm and its deflection angle α is 45°. The results of the study show that there is an inhibitory effect on the discrete noise of axial flow fan with perforated blade on the tip area, and its total noise level emerged as the fluctuated distribution characteristics with the increase in the perforation diameter D and reduced along with the increase in the deflection of perforation angle α, at the same time varied as a linear characteristics, which can be reasonably explained by the acoustic interference theory. The results of the study have also further confirmed that the improvement of the flow of axial flow fan with perforated blade helps to reduce the pressure pulsation amplitude caused by the turbulence of the blade surface boundary layer, thereby suppressing the back-flow and vortex from the pressure surface to the suction surface efficiently. It is indicated that the improved vortex shedding phenomenon at the blade trailing edge after perforation on the area of blade tip is the main reason for the aerodynamic noise reduction of axial flow fan.

An experimental investigation on the tip leakage noise in axial-flow fans with rotating shroud

The tip leakage noise generated by a shrouded rotor of an axial-flow fan has been experimentally studied. The measurements have been taken at high flow rate and at the design point in a hemi-anechoic chamber, at constant rotational speed and during speed ramps. A test plenum designed according to ISO 10302 has been employed to modify the operating conditions and different inlet configurations, ducted and unducted with standard and reduced tip gap, have been considered. The basic features of the inflow have been studied by means of aerodynamic measurements taken upstream of the rotor. To separate the noise generating mechanisms from the acoustic propagation effects, the acoustic response function of the test configuration has been computed employing the spectral decomposition method, and then it has been compared with the velocity-scaled, constant-Strouhal number SPL. In this way, the noise components related to the tip leakage flow have been identified and their connection with geometry have been highlighted. The broadband part of the spectra and the peaks related to the tip leakage flow are affected by the same propagation effects, but show a different dependence on the rotational speed and on the operating point. The upstream geometry affects the radiated noise much more than the performance and even a strong reduction in the tip-gap cannot completely eliminate the related noise.

Numerical predictions of the broadband turbulent noise for axial flow cooling fans

A statistical model was established in this article for predicting the broadband turbulent noise of axial flow fans. First, an integral formula was deduced based on the Ffowcs Williams-Hawkings (FW-H) equations for the purpose of calculating the sound power spectrum of aeroacoustic sources with low rotating speed. The auto-correlation spectrum of the fluctuating pressure on the fan blades was modeled by a two-section exponential function. The characteristic aerodynamic parameters, such as boundary layer thickness, external flow velocity, wall shear stress, and average static pressure gradient on blade surfaces, were obtained by solving the steady Reynolds-averaged Navier-Stokes equations and used to normalize the auto-correlation spectrum. Then, the unknown coefficients in the exponential function were determined by fitting the experimental noise spectra for two typical and commercially available axial flow cooling fans. Finally, under the conditions of retaining the similar aerodynamic performances of the two baseline fans, a new fan design was developed and optimized using this method, of which the overall noise level was 2 dB lower than the quieter of the two baseline fans. The predicted noise spectra for all three fans agreed very well with the experimental data.

Active Control of Axial-flow Fan Noise Using Magnetic Bearings

In this paper we present a novel approach to reducing blade-rate noise of axial-flow fans. By using magnetic bearings as a noise control actuator, it is possible to collocate the anti-noise source with the disturbance noise source. This approach allows for global noise reduction throughout the sound field. A DC motor connected to a fan by a short rigid shaft was used to demonstrate this approach. The shaft was supported in the radial and axial directions by magnetic bearings. The bearings provide position control of the shaft and fan; this position control can be used to vibrate the fan at a desired frequency and amplitude. Controlled vibration of the fan allows its use as a speaker in an active noise control scheme. Noise control was implemented on a dedicated digital signal processor using a least mean square algorithm. The output of the noise control algorithm supplies the position commands for the magnetic bearing controller. Experimental data showed that by actuating the axial thrust bearing, the noise output of a fan could be reduced by 4 dB at the error microphone, and 3 dB at points away from the error microphone.

Experimental Research for Performance Improvement and Noise of Axial Flow Fan

Experimental Research for Performance Improvement and Noise of Axial Flow Fan

Tip clearance noise of axial flow fans operating at design and off-design condition

The noise due to tip clearance (TC) flow in axial flow fans operating at a design and off-design conditions is analyzed by an experimental measurement using two hot-wire probes rotating with the fan blades. The unsteady nature of the spectra of the real-time velocities measured by two hot-wire sensors in a vortical flow region is investigated by using cross-correlation coefficient and retarded time of the two fluctuating velocities. The results show that the noise due to TC flow consists of a discrete frequency noise due to periodic velocity fluctuation and a broadband noise due to velocity fluctuation in the blade passage. The peak frequencies in a vortical flow are mainly observed below at four harmonic blade passing frequency. The discrete frequency component of velocity fluctuation at the off-design operating conditions is generated in vortical flow region as well as in reverse flow region. The peak frequency can be an important noise source when the fans are rotated with a high rotational speed. The authors propose a spiral pattern of velocity fluctuation in the vortical flow to describe the generation mechanism of the peak frequency in the vortical flow. In addition, noise increase due to TC flow at low flow rate condition is analyzed with relation to the distribution of velocity fluctuation due to the interference between the tip leakage vortex and the adjacent pressure surface of the blade.

Hybrid active and passive control of fan noise

This paper deals with the global reduction of axial flow fan noise in ducts in a building using a hybrid passive–active noise control method. The effectiveness of using an infra-red device as a reference signal source is also investigated. It is shown that using such a hybrid noise control system over an axial-flow fan reduces the overall sound pressure level by 5 dB(A) in the surrounding environment and global control of the blade passing frequency can also be achieved. This paper also shows that using an infra-red device as a reference signal source produces marginally better control as compared with using a microphone reference sensor. Moreover, long term stability is guaranteed and the possibility of acoustic feedback is eliminated.

Axial Flow Fan Noise Generated by the Interaction between Tip Leakage Flow and an Adjacent Rotor Blade

To clarify the mechanism of noise generation from a low pressure axial flow fan, time fluctuating velocity was measured around the rotor blades, especially near the rotor tip, by using a hot-wire sensor from a relative flame of reference fixed to the rotor blades. Two sensors were used to obtain the cross-correlation between velocity fluctuations at the reference point and other locations. The results are summarized as follows. If the flow rate was lower than the design condition and the tip leakage flow became to attach to the following blade, the sound pressure level was increased. From the cross-correlation of velocity fluctuations the leakage flow flew downstream spirally, in which a discrete frequency velocity component with low frequency was predominant. It is possibly considered to be the cause of the noise generation of low frequency band.

3936 軸流送風機騒音の伝播特性と能動制御を用いた騒音低減

3936 軸流送風機騒音の伝播特性と能動制御を用いた騒音低減

Active control of axial-flow fan noise

Discrete-frequency axial-flow fan noise reduction using active noise control is described. The unique aspect of the current research is the use of the fan itself as the antinoise source in the active noise control scheme. This is achieved by driving the entire fan unit axially with an electrodynamic shaker which mechanically couples the solid surfaces of the fan to the acoustic medium. The fan unit is thus transformed into a crude loudspeaker. A near-field microphone serves as an error sensor, where transfer function measurements between the electrical input to the shaker and the electrical output of the microphone are found to be reasonably free of phase distortions and linear. A feedforward algorithm utilizing the output of a tachometer as a reference signal is used. The experimental apparatus is composed of a baffled fan unit in a free field. A small cylindrical flow obstruction is placed on the inlet side of the fan to enhance noise emissions at the blade-pass frequency and harmonics. The experiment successfully demonstrates the concept of active control of tonal fan noise using a shaken fan as the cancellation source. For the fan operating in a planar baffle, the fundamental blade-passage frequency sound-pressure level at the location of the error sensor is reduced by 20 dB, while the second and third harmonic levels are reduced by 15 and 8 dB, respectively. Placing a cabinet enclosure over the baffled fan did not affect these results significantly, and free-field sound power measurements indicate similar level reductions with the active control in operation.

Generation Mechanism of the Unusual Noise in Axial Flow Fans Driven by Induction Motors.

Generation Mechanism of the Unusual Noise in Axial Flow Fans Driven by Induction Motors.

Active control of axial-flow fan noise

An investigation was conducted using active noise control to reduce noise from small axial-flow fan units commonly found in computers and printers. The fan unit itself was used as the cancellation source in the active noise control scheme, achieved by axially modulating the unit with a shaker. Feasibility studies which looked at radiation efficiency and transfer function data identified fan units which would adequately perform as efficient, undistorted sources of noise when driven by particular shakers. Once a suitable shaker and fan combination was discovered, simulations of active noise control were conducted in MATLAB which utilized the measured error path impulse response (representing the system which defines the output voltage response of a microphone near the fan to an input voltage supplied to the shaker). Results from the simulation showed that an experiment could be constructed which would effectively reduce the tonal components from the fan unit. An experimental demonstration was constructed, results from which show a 20-dB reduction in sound-pressure level for the blade passage tone, a 15-dB reduction for the second harmonic, and a 7- to 8-dB reduction for the third harmonic. [Work supported by IBM through Shared University Research Program.]

Control of Axial Flow Fan Noise by Design

This paper discusses the present methods of controlling tonal noise in axial flow fans and puts forward some basic parameters for use in the design and selection of this product. Descriptions are given of the effects of fan casing geometry, the interaction of fixed duct elements and fan rotating parts, the effect of inlet disturbance and changes in noise level with radial clearance. Finally, guidelines are given for users of axial How fans in order to minimise noise levels.