Centrifugal Fan Noise Research Articles

Effect of impeller structure on aerodynamic performance and noise reduction of a small multi-blade centrifugal fan

In this study, the numerical simulation and orthogonal test are combined to study the effects of blade outlet angle, blade inlet angle, and blade number on the centrifugal fan flow characteristics, stress distribution, and noise control. The experimental tests were carried out to confirm the accuracy of the computational model. The computational fluid dynamics (CFD) technology was used to establish 16 groups of impeller models and derive the optimal parameter combination form. The results show that the blade inlet angle and outlet angle have more significant effects on efficiency and flow rate of fans. Among different optimize structures, the A8 fan with an inlet angle of 60°, an outlet angle of 180°, and a blade number of 45, has the best aerodynamic performance, with a 17.4% increase in flow rate, a 3.3% increase in efficiency, a 7.6% reduction in noise and a 23.0% reduction in impeller stress, compared to the original fan. Reasonable adjustment of the inlet and outlet angles greatly improves fluid distribution and suppresses flow separation. Furthermore, the noise can be reduced by lessening the disturbance between the volute tongue and wake flow, so the flow state gets greatly improved at the volute tongue region.

The aerodynamic and noise characteristics of centrifugal fan with partially tilted tongue

Tilted tongue is one of the very effective solutions to reduce the noise of centrifugal fans. In this study, the accuracy of the numerical simulations is verified by experimentally measured aerodynamic performance and acoustic spectra. Two localized tilting designs of the tongue are proposed with the aim of reducing the aerodynamic noise of the centrifugal fan. Numerical results show that the different approaches significantly affect the noise reduction of the fan, with the best design exhibiting up to 2.33 dB of noise reduction. The internal flow and acoustic fields are analyzed in conjunction with the dynamic modal decomposition method to reveal the effect of the local tilt of the tongue on the flow and acoustic characteristics of the fan. The structural change induces the separation vortices at the trailing edge of the blades and the generation of secondary flow at the outlet wall of the volute shell, which is the main reason for the slight degradation of the aerodynamic characteristics of the fan. The causes of the blade passage frequency (BPF) noise reduction are not identical for different orders. BPF noise reduction stems from diminishing source intensity and dispersing source phase. Noise reduction in 2BPF is mostly due to weakening sound source intensity, with less conspicuous phase dispersion. This study provides good theoretical support for the design of backward curved centrifugal fans in the context of noise reduction.

An Empirical noise model of centrifugal fans with different volute tongues based on Langevin regression

In the context of the rapidly evolving field of building ventilation, fan noise control stands out as a pivotal technology to enhance the quality of life. This study aimed to elucidate the inherent randomness, distinct characteristics, and potential low-dimensional noise structure essential for developing effective noise control methods. In this study, a stochastic dynamics model for the noise of centrifugal fans with various volute tongue structures is constructed using the Langevin regression method and experimental measurements. An empirical noise model capturing the peak characteristics of noise discrete tonal is developed through parametric mode expansion and an empirical mean-field model of turbulent wakes, facilitating accurate noise predictions. The research findings demonstrate the effectiveness of the Langevin equation employing the cubic Stuart-Landau equation and multiplicative noise to predict fan noise across different volute tongue structures. While stochastic dynamics models unavoidably lose the characteristic discrete noise peaks, predictions of the total A-weighted sound pressure level remain within a 2.2% error margin. The stochastic dynamics models applied to centrifugal fan aerodynamic noise and turbulent wakes exhibit striking resemblances, suggesting a fundamental connection between turbulence and noise generation. The extended empirical noise model maintains discrete pitch noise peaks by introducing shift modes, indicating that stronger Langevin deformations correspond to larger translational amplitudes of the shift modes. The advancement of stochastic dynamics and empirical noise models lays a foundational framework for the formulation of effective noise control strategies.

A Review of Bionic Structures in Control of Aerodynamic Noise of Centrifugal Fans

Due to the complexity of the working conditions and the diversity of application scenarios, the normal operation of a fan, whether volute tongue, volute shell surface, or blade, often encounters some unavoidable problems, such as flow separation, wear, vibration, etc.; the aerodynamic noise caused by these problems has a significant impact on the normal operation of the fan. However, despite the use of aerodynamic acoustics to design low-noise fans or the use of sound absorption, sound insulation, and sound dissipation as the main traditional noise control techniques, they are in a state of technical bottleneck. Thus, the search for more efficient methods of noise reduction is looking toward the field of bionics. For this purpose, this paper first analyzes the mechanism of fan noise in the volute tongue and blades, and then, this paper reviews the noise control mechanism and improvement research using the bionic structures in the volute tongue structure, the contact surface of the volute shell, and the leading and trailing edges of the blade in the centrifugal fan. Finally, the current challenges and prospects of bionic structures for aerodynamic noise control of centrifugal fans are discussed.

Flow Control Mechanism of Blade Tip Bionic Grooves and Their Influence on Aerodynamic Performance and Noise of Multi-Blade Centrifugal Fan

To improve the aerodynamic performance and reduce the noise of multi-blade centrifugal fans used in air conditioners, a bionic groove structure was introduced into the blade tip design, inspired by the drag reduction characteristics of mantis shrimp. In this paper, the numerical method was used to investigate the effects of a blade tip bionic groove on the aerodynamic performance and noise characteristics of a multi-blade centrifugal fan. Firstly, the basic design parameters, such as groove width, groove depth, groove center distance, and groove number, were selected to define the shape of the blade tip bionic groove. Then, the effect of the design parameters on the aerodynamic performance of the multi-blade centrifugal fan was studied. Finally, the multi-blade centrifugal fan models with different groove shapes, such as rectangular bionic grooves, circular bionic grooves, and triangular bionic grooves, were established to compare the influence of blade tip groove structures on the aerodynamic performance of the multi-blade centrifugal fan. Through analysis of the aerodynamic performance and noise characteristics of the multi-blade centrifugal fan and the flow fields in the fan impeller, the flow control mechanism of the blade tip bionic groove was revealed. The results showed that the triangular bionic groove on the blade tip had a certain noise reduction effect, although the structural parameters of the bionic groove had little effect on the aerodynamic performance of the multi-blade centrifugal fan. This is because the triangular bionic groove structure can effectively inhibit the vortex shedding at the trailing edge of blade and reduce the flow separation in the impeller passages. As a result, the velocity distribution at the impeller tip became more uniform and the intensity of the tip vortex and the shedding vortex was weakened. Correspondingly, the noise of multi-blade centrifugal fan was also reduced to some extent.

Aerodynamic noise prediction of a high-speed centrifugal fan considering impeller-eccentric effect

ABSTRACT In this paper, the aerodynamic noise of a centrifugal fan with an eccentric impeller is investigated and analyzed by adopting a hybrid method combining detached-eddy simulation and the acoustic finite element method (FEM). The impeller-eccentric effect of high-speed centrifugal fans, frequently ignored in theoretical studies, is objective in practical engineering applications owing to machining and installation errors, which have a significant influence on flow characteristics and subsequently noise characteristics. An impeller-whirling model combined with the sliding mesh method is introduced to obtain the actual flow with an eccentric impeller. First, the internal flow field handled with different eccentricities is investigated. The total pressure and internal efficiency decline, and the flow field near the leading edge shows intense unsteadiness, inducing a rise in the pressure fluctuation amplitude at the rotating frequency (RF) in both impeller flow passage and volute domain. Second, the variational formulation of Lighthill’s analogy is implemented by acoustic FEM to better account for the interaction between the solid surface and aerodynamic sound, capturing a contribution by turbulence noise at the second RF. Under eccentric conditions, the sound source intensity shows a circumferential non-uniform distribution in a similar region to the flow field. The calculated sound pressure level captures the variation in the experimental result, which shows an obvious rise at RF induced by the impeller-eccentric effect. The characteristics of the noise spectrum and sound directivity change significantly, and the overall sound pressure level rises with the increase in eccentricity. This study provides an effective simulation strategy for predicting the aerodynamic noise of centrifugal fans under realistic conditions.

Optimal design of multi-blade centrifugal fan based on partial coherence analysis

Considering that there are many design variables in multi-blade centrifugal fans, the complicated design parameters and internal flow uncertainty increase the difficulty of studying fan noise mechanisms. This study adopted the impact noise between the airflow at the impeller outlet inside the fan and the volute tongue as the research object. Based on the influence of mutual interfering noise sources on the system noise, a partial coherence function was introduced to establish a system noise model. The correlation between the static pressure of the impeller outlet in the volute tongue area of the centrifugal fan and far-field noise of the fan was analyzed and obtained. The peak values of fundamental frequency and average sound pressure level of a far-field noise receiving points were selected as the optimization goals, taking the volute tongue placement angle θ1, volute tongue radius R, and center distance L1 as the optimization objects. The Latin hypercube sampling was used to select 35 groups of sampling points and a Kriging agent model was established. The NSGA-II genetic algorithm was used to optimize the volute tongue profile. The results showed that the flow rate was increased by 1.2 m3/min, the far field noise of the centrifugal fan was reduced by 1.9 dB, while the fan efficiency increased by 3%, static pressure increased by 27 Pa, and peak values of fundamental frequency reduced by 8%.

Reducing Occupational Noise Propagated from Centrifugal Fan through Dissipative Silencers: A Field Study

Acoustic performance of dissipative silencer was evaluated to determine the effectiveness of perforated duct porosity and absorbent material density in reducing occupational noise exposure propagated from centrifugal fan. Design charts were applied to predict noise reduction and length of a dissipative silencer. Dissipative silencers with various punched duct porosity (14%, 30% and 40%) and sound absorbent density (80 Kg/m3 , 120 Kg/m3 , and 140 Kg/m3 ) were designed and fabricated. According to ISO9612 and ISO11820, noise level was measured before and after installing all nine test silencers at fixed workstations around the discharge side of a centrifugal fan in a manufacturing plant. On average, the noise level at the discharge side of a fan without silencer was measured to be 93.6 dBA, whereas it was significantly mitigated by 67.4 dBA to 70.1 dBA after installing all silencers. Dynamic insertion loss for a dissipative silencer with 100 cm length was predicted to be 27.9 dB, which was in agreement with experimental ones. Although, there was no significant differences between insertion loss of silencers, the one with 30% porosity and 120 Kg/m3 rock wool density had the highest insertion loss of 26.2 dBA. Dissipative silencers noticeably reduced centrifugal fan noise exposures. Increasing sound absorbent density and duct porosity up to a certain limit could probably be effective in noise reduction of dissipative silencers.

Noise Prediction of Centrifugal Fan Based on Improved Nenral Network

In order to solve the problems that the prediction accuracy of the traditional centrifugal fan is low and the cost is high, a noise prediction model for centrifugal fan based on improved particle swarm optimization (IPSO) optimized BP neural network was presented. The initial weights and thresholds of BP neural network were optimized by using IPSO. The 17 parameters were collected by the liancheng company and be used to establish the regression equation to obtain the standard regression coefficient. The importance of the fan parameters was ranked and four key characteristic parameters were determined as input values by the optimization algorithm to build the IPSO-BP centrifugal fan noise prediction model. After comparative study, IPSO-BP model has better prediction effect than PSO-BP model and BP model, and the prediction error is only 0. 97%. The research shows that IPSO-BP model can effectively shorten the fan design period and save the design cost.

Experimental investigation of metal foam for controlling centrifugal fan noise

This paper presents an experimental investigation on the metal foam for controlling a centrifugal fan noise. Nine samples of metal foam with different types of cells, i.e., open, semi-open and close, are employed to compare their effects on the aerodynamic performance and noise level of the centrifugal fan. Experimental data confirms that the open cell metal foam is the most effective to control the fan noise because it not only significantly suppresses the tonal noise but also attenuates the broadband noise. Moreover, the geometrical parameters of the open cell metal foam, i.e., pores per inch and porosity, are studied to investigate their effects on the aerodynamic performance and noise level of the centrifugal fan.

Passive control of centrifugal fan noise by employing open-cell metal foam

Experimental and numerical studies were conducted to investigate passive control of a forward-curved centrifugal fan noise by employing the open-cell metal foam (OCMF). The results indicated that a reduction of about 5dB in overall A-weighted sound pressure level (OASPL) was successfully achieved with a decline of about 200Pa in total pressure rise (TPR). For the OCMF investigated in the present paper with the pores per inch (PPI) of 20 and the porosity of 97%, the noise control mechanism was to suppress the source strength of tonal noise generated from the periodic impeller–tongue interaction rather than to absorb the broadband acoustic energy. The decline of the aerodynamic performance was mainly caused by reducing the work capacity of the impeller rather than caused by flow loss owing to the flow resistance of the OCMF. An improved design of the OCMF was suggested to achieve more reduction in noise level with less decline of aerodynamic performance.

Unsteady Fast Random Particle Mesh method for efficient prediction of tonal and broadband noises of a centrifugal fan unit

In this study, efficient numerical method is proposed for predicting tonal and broadband noises of a centrifugal fan unit. The proposed method is based on Hybrid Computational Aero-Acoustic (H-CAA) techniques combined with Unsteady Fast Random Particle Mesh (U-FRPM) method. The U-FRPM method is developed by extending the FRPM method proposed by Ewert et al. and is utilized to synthesize turbulence flow field from unsteady RANS solutions. The H-CAA technique combined with U-FRPM method is applied to predict broadband as well as tonal noises of a centrifugal fan unit in a household refrigerator. Firstly, unsteady flow field driven by a rotating fan is computed by solving the RANS equations with Computational Fluid Dynamic (CFD) techniques. Main source regions around the rotating fan are identified by examining the computed flow fields. Then, turbulence flow fields in the main source regions are synthesized by applying the U-FRPM method. The acoustic analogy is applied to model acoustic sources in the main source regions. Finally, the centrifugal fan noise is predicted by feeding the modeled acoustic sources into an acoustic solver based on the Boundary Element Method (BEM). The sound spectral levels predicted using the current numerical method show good agreements with the measured spectra at the Blade Pass Frequencies (BPFs) as well as in the high frequency range. On the more, the present method enables quantitative assessment of relative contributions of identified source regions to the sound field by comparing predicted sound pressure spectrum due to modeled sources.

Validation of numerical prediction method of BPF noise for industrial centrifugal fans

Blade passing frequency (BPF) noise is the dominating component of the flow induced noise of centrifugal fans. The numerical methods for BPF noise prediction, based on the computational aeroacoustics (CAA), have been published for decades. However, there are a couple of challenges for accurately predicting noise for industrial centrifugal fans. The first arises from the fact that the free field hypothesis, adopted in the numerical model, has not yet been carefully studied. The second challenge stems from the current criteria for which the prediction results are compared to the measurement data. Because the test conditions do not always satisfy the requirements of the numerical model, inaccurate predictions occasionally resulted. Therefore, since the prediction results may deviate largely from the test data, the applicability of these methods is severely limited.

Multi-objective optimization design and experimental investigation of centrifugal fan performance

Current studies of fan performance optimization mainly focus on two aspects: one is to improve the blade profile, and another is only to consider the influence of single impeller structural parameter on fan performance. However, there are few studies on the comprehensive effect of the key parameters such as blade number, exit stagger angle of blade and the impeller outlet width on the fan performance. The G4-73 backward centrifugal fan widely used in power plants is selected as the research object. Based on orthogonal design and BP neural network, a model for predicting the centrifugal fan performance parameters is established, and the maximum relative errors of the total pressure and efficiency are 0.974% and 0.333%, respectively. Multi-objective optimization of total pressure and efficiency of the fan is conducted with genetic algorithm, and the optimum combination of impeller structural parameters is proposed. The optimized parameters of blade number, exit stagger angle of blade and the impeller outlet width are seperately 14, 43.9°, and 21 cm. The experiments on centrifugal fan performance and noise are conducted before and after the installation of the new impeller. The experimental results show that with the new impeller, the total pressure of fan increases significantly in total range of the flow rate, and the fan efficiency is improved when the relative flow is above 75%, also the high efficiency area is broadened. Additionally, in 65% −100% relative flow, the fan noise is reduced. Under the design operating condition, total pressure and efficiency of the fan are improved by 6.91% and 0.5%, respectively. This research sheds light on the considering of comprehensive effect of impeller structrual parameters on fan performance, and a new impeller can be designed to satisfy the engineering demand such as energy-saving, noise reduction or solving air pressure insufficiency for power plants.

Theoretical and experimental studies on the noise control of centrifugal fans combining absorbing liner and inclined tongue

In previous work, it has been validated that the inclined tongue has a significant effect on controlling the tonal noise of centrifugal fans. In order to reduce the broadband noise of centrifugal fans, theoretical and experimental research studies have been implemented to study the effect of the sound-absorption volute on noise propagation. First, a mathematical–physical model of the sound-absorption volute is established to explore the influence of the sound-absorption coefficient of the liner, which is dependent on the liner thickness, cavity depth, etc. Then, an experimental study is carried out to measure the coupling effect between the absorbing liner and the inclined tongue and its potential for the noise control of centrifugal fans. The experimental results agree well with the theoretical result, and validate the mathematical–physical model, proving it a practical model for further optimization of the sound-absorption volute. In addition, the results indicate that considerable noise reduction can be achieved by combining both the posed absorbing liner and modified inclined tongue.

Study of Tonal Fan Noise Reduction by Modification of the Volute Cutoff

Blade-passing frequency (BPF) tonal noise is usually the main contributor to centrifugal fan noise as opposed to broad-band noise; therefore, abating its strength can reduce fan noise significantly. The predominant BPF noise source is the surface acoustic dipole over the cutoff due to the flow interactions between the impeller and the volute. In this study, a modified cutoff with an inclined edge and enlarged cutoff clearance was successfully employed to reduce the BPF noise; the measured noise spectra at three different flow rates of the inclined-cutoff fan and the original fan were compared, and noticeable noise reduction was found. The cause of this tonal noise reduction was numerically studied, using computational fluid dynamics (CFD) technology and acoustic analogy theory to calculate the flow fields inside the fan and sound radiation respectively. Results showed that the cutoff, including the geometric configuration and it's clearance with the impeller, was crucial to impeller-volute flow interactions. As a consequence, this inclined cutoff with enlarged cutoff clearance could eliminate the BPF pressure fluctuation, i.e. BPF dipole source, at the design point effectively; although the BPF pressure fluctuation was still notable at large flow rates, the radiated sound power decreased drastically attributed to the phase cancellation of the dipole sources. This study shows that CFD combined with acoustic analogy can provide a reliable access to noise prediction, thus it will be employed in aeroacoustic optimization of centrifugal fans.

Experimental study on the noise reduction of an industrial forward-curved blades centrifugal fan

Many previous researches have concentrated on the noise of backward-curved (BC) blades and forward-curved (FC) multi-blade centrifugal fans. In this paper, an experimental study has been carried out to study the noise reduction of an industrial FC blades centrifugal fan. First of all, the performance and noise characteristics of the FC centrifugal fan were tested to compare the similarities and differences from those of BC blades and FC multi-blade centrifugal fans. And then, some different volute geometric configurations were carried out in order to study the effects of inclined volute tongue, impeller blade-tongue clearance, hub-volute clearance and their coupling effect to the performance and noise of the FC blades centrifugal fan. The aim of many different experimental tests is to validate whether the effects of different modifications to fan performance and noise are additive and to find a good impeller-volute matching to reduce the centrifugal fan noise without reducing performance. The experimental results show that a good coupled modification not only could reduce the fan noise but also could advance the fan performance and extend the operating range.

Noise Prediction of a Centrifugal Fan: Numerical Results and Experimental Validation

Centrifugal fans are widely used in several applications, and in some cases, the noise generated by these machines has become a serious problem. The centrifugal fan noise is frequently dominated by tones at the blade passing frequency as a consequence of the strong interaction between the flow discharged from the impeller and the volute tongue. In this study, a previously published aeroacoustic prediction methodology (Cho, Y., and Moon, Y.J., 2003, “Discrete Noise Prediction of Variable Pitch Cross-Flow Fans by Unsteady Navier-Stokes Computations,” ASME J. Fluids Eng., 125, pp. 543–550) has been extended to three-dimensional turbulent flow in order to predict the noise generated by a centrifugal fan. A three-dimensional numerical simulation of the complete unsteady flow on the whole impeller-volute configuration has been carried out using the computational fluid dynamics code FLUENT®. The unsteady forces applied by the fan blades to the fluid are obtained from the data provided by the simulation. The Ffowcs Williams and Hawkings model extension of Lighthill’s analogy has been used to predict the aerodynamic noise generated by the centrifugal fan from these unsteady forces. Also, the noise generated by the fan has been measured experimentally, and the experimental results have been compared to the numerical results in order to validate the aerodynamic noise prediction methodology. Reasonable agreement has been found between the numerical and the experimental results.

Effect of discharge duct geometry on centrifugal fan performance and noise emission

Non-ideal inlet and discharge duct geometries can cause significant changes to both the aerodynamic performance (‘‘fan curve’’) and specific sound power emission of a fan. A proper understanding of actual installed performance, as well as a good estimate of the system backpressure curve, is critical to achieving flow and acoustic goals as well as other criteria such as power consumption, mass and volume. To this end a battery of ISO 10302 tests was performed on a blower assembly which supports the Advanced Animal Habitat, being developed by ORBITEC for deployment on the International Space Station. The blower assembly consists of (4) identical centrifugal fans that, amongst themselves and across two prototypes, incorporated several discharge geometries. The inlet geometries were identical in all cases. Thus by comparing the dimensionless pressure-flow and noise emission characteristics across the cases, significant insight into the nature and potential magnitude of these effects is gained.

Implementation of adaptive harmonic noise controller for engine exhaust system with frequency multiplier circuit

A novel active noise control (ANC) technique using adaptive frequency multiplier circuit for blade passing frequency (BPF) noise of centrifugal fan and harmonic noise of engine exhaust system is proposed. The proposed ANC system is based on the well-known adaptive controller with filtered-x least-mean-square (FXLMS) using variable step size convergence technique. The proposed controller is realised on finite impulse response (FIR) filter and implemented by using a TMS320C32 digital signal processor (DSP) with reference signal from optical fibre sensor and frequency multiplier circuit. Experiments are carried out to evaluate the noise attenuation of the proposed ANC system for centrifugal fan and engine exhaust system. The experimental results indicate that the frequency multiplier circuit could improve the performance in reducing the noise at the BPF of centrifugal fan and periodic noise of exhaust system.