Noise reduction mechanisms for the inclined leading edge vaned diffuser in a centrifugal fan

2017 ◽  
Vol 231 (1) ◽  
pp. 68-83 ◽  
Author(s):  
Gong Wu Qi ◽  
Zhang Wei
Keyword(s):  
Noise Reduction ◽  
Pressure Fluctuation ◽  
Numerical Study ◽  
Second Harmonic ◽  
Leading Edge ◽  
Centrifugal Fan ◽  
Fan Noise ◽  
Vaned Diffuser ◽  
Reduction Mechanisms ◽  
Centrifugal Fans

An experimental and numerical study to explore the noise reduction mechanism for the inclined leading edge vaned diffuser in centrifugal fans is described. Inclined leading edge vaned diffuser is useful in improving fan performance, increasing operating range, and reducing fan noise. The generation of fan noise is related to the pressure fluctuation on the diffuser vane surface, particularly the leading edge. Numerical results show that pressure fluctuation on the inclined leading edge vaned diffuser surface remarkably decreases, unlike that of the original diffuser. The pressure fluctuation is dominated by the components at the blade passing frequency and its second harmonic.

Experimental Study for the Effect of Vaned Diffuser Leading Edge on the Noise Generated From a Centrifugal Fan

2009 ◽  
Author(s):  
Wei Zhang ◽  
Wu Qi Gong ◽  
Xiao Hua Fan ◽  
Guang Xi
Keyword(s):  
Leading Edge ◽  
Flow Coefficient ◽  
Centrifugal Fan ◽  
Test Results ◽  
Fan Noise ◽  
Experimental Conditions ◽  
Vaned Diffuser ◽  
Flow Rate Coefficient ◽  
Aerodynamic Performances ◽  
Inclined Angle

This paper studies a novel vaned diffuser with inclined leading edge to reduce the fan noise. The aerodynamic performances and sound pressure level (SPL) of the centrifugal fan with five different diffusers were measured in an anechoic chamber, and the inclined angles of the five diffusers are 45°, 60°, 120°, 135° and 150°, respectively. The flow coefficient of the fan varies from 0.037 to 0.14, the rotational speed ranges from 20000rpm to 35000rpm. The test results show that, by using diffuser vanes with inclined leading edge, the overall noise of the fan is reduced in the experimental conditions, and it has the minimum value at the flow rate coefficient of 0.084. The overall noise reduction of 5.3dB was made with the diffuser leading edge inclined angle of 150°.

Numerical study on the airfoil self-noise of three owl-based wings with the trailing-edge serrations

2021 ◽  
pp. 095441002098822
Author(s):  
Dian Li ◽  
Xiaomin Liu ◽  
Lei Wang ◽  
Fujia Hu ◽  
Guang Xi
Keyword(s):  
Flow Field ◽  
Noise Reduction ◽  
Numerical Study ◽  
Barn Owl ◽  
Aerodynamic Noise ◽  
Frequency Noise ◽  
Trailing Edge ◽  
Reduction Mechanisms ◽  
Trailing Edge Serrations ◽  
Bionic Airfoil

Previous publications have summarized that three special morphological structures of owl wing could reduce aerodynamic noise under low Reynolds number flows effectively. However, the coupling noise-reduction mechanism of bionic airfoil with trailing-edge serrations is poorly understood. Furthermore, while the bionic airfoil extracted from natural owl wing shows remarkable noise-reduction characteristics, the shape of the owl-based airfoils reconstructed by different researchers has some differences, which leads to diversity in the potential noise-reduction mechanisms. In this article, three kinds of owl-based airfoils with trailing-edge serrations are investigated to reveal the potential noise-reduction mechanisms, and a clean airfoil based on barn owl is utilized as a reference to make a comparison. The instantaneous flow field and sound field around the three-dimensional serrated airfoils are simulated by using incompressible large eddy simulation coupled with the FW-H equation. The results of unsteady flow field show that the flow field of Owl B exhibits stronger and wider-scale turbulent velocity fluctuation than that of other airfoils, which may be the potential reason for the greater noise generation of Owl B. The scale and magnitude of alternating mean convective velocity distribution dominates the noise-reduction effect of trailing-edge serrations. The noise-reduction characteristic of Owl C outperforms that of Barn owl, which suggests that the trailing-edge serrations can suppress vortex shedding noise of flow field effectively. The trailing-edge serrations mainly suppress the low-frequency noise of the airfoil. The trailing-edge serration can suppress turbulent noise by weakening pressure fluctuation.

scholarly journals A Numerical Study of Aerodynamic Performance and Noise of a Bionic Airfoil Based on Owl Wing

2014 ◽  
Vol 6 ◽  
pp. 859308 ◽  
Author(s):  
Xiaomin Liu ◽  
Xiang Liu
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Noise Reduction ◽  
Numerical Study ◽  
Aerodynamic Performance ◽  
Centrifugal Fan ◽  
Surface Geometry ◽  
Airfoil Surface ◽  
Acoustic Sources ◽  
Bionic Airfoil

Noise reduction and efficiency enhancement are the two important directions in the development of the multiblade centrifugal fan. In this study, we attempt to develop a bionic airfoil based on the owl wing and investigate its aerodynamic performance and noise-reduction mechanism at the relatively low Reynolds number. Firstly, according to the geometric characteristics of the owl wing, a bionic airfoil is constructed as the object of study at Reynolds number of 12,300. Secondly, the large eddy simulation (LES) with the Smagorinsky model is adopted to numerically simulate the unsteady flow fields around the bionic airfoil and the standard NACA0006 airfoil. And then, the acoustic sources are extracted from the unsteady flow field data, and the Ffowcs Williams-Hawkings (FW-H) equation based on Lighthill's acoustic theory is solved to predict the propagation of these acoustic sources. The numerical results show that the lift-to-drag ratio of bionic airfoil is higher than that of the traditional NACA 0006 airfoil because of its deeply concave lower surface geometry. Finally, the sound field of the bionic airfoil is analyzed in detail. The distribution of the A-weighted sound pressure levels, the scaled directivity of the sound, and the distribution of dP/dt on the airfoil surface are provided so that the characteristics of the acoustic sources could be revealed.

A Numerical Study of the Blade Passing Frequency Noise of a Centrifugal Fan

2012 ◽  
Author(s):  
Jian-Cheng Cai ◽  
Da-Tong Qi ◽  
Yong-Hai Zhang
Keyword(s):  
Pressure Fluctuation ◽  
Sound Radiation ◽  
Aerodynamic Noise ◽  
Sound Power ◽  
Centrifugal Fan ◽  
Structural Noise ◽  
Tonal Noise ◽  
Fan Noise ◽  
Blade Passing Frequency ◽  
Dipole Sources

Tonal noise constitutes the major part of the overall fan noise, especially the blade passing frequency (BPF) noise which is generally the most dominant component. This paper studies the BPF tonal noise of a centrifugal fan, including the blade noise, casing aerodynamic noise, and casing structural noise caused by the flow-induced casing vibration. Firstly, generation mechanism and propagation process of fan noise were discussed and the measured spectra of fan noise and casing vibration were presented. Secondly, a fully 3-D transient simulation of the internal flow field of the centrifugal fan was carried out by the computational fluid dynamics (CFD) approach. The results revealed that the flow interactions between the impeller and the volute casing caused periodic pressure fluctuations on the solid walls of the impeller and casing. This pressure fluctuation induces aerodynamic noise radiation as dipole sources, as well as structural vibration as force excitations. Thirdly, using the acoustic analogy theory, the aeroacoustic dipole sources on the casing and blade surface were extracted. The BPF casing and blade aerodynamic sound radiation were solved by the boundary element method (BEM) taking into account the scattering effect of the casing structure. Finally, the casing structural noise was studied. The casing forced vibration and sound radiation under the excitation of BPF pressure fluctuation were calculated by finite element method (FEM) and BEM, respectively. The result indicates that at the studied flow rate, the sound power levels of the casing aerodynamic noise, blade aerodynamic noise and casing structural noise are 103 dB, 91 dB and 79 dB with the reference sound power of 1×10−12 W, respectively.

Flow Survey of a Forward Curved Blades Centrifugal Fan for HVAC Applications

2016 ◽  
Author(s):  
Fabio Breviario ◽  
Dario Brivio ◽  
Lucio Cardillo ◽  
Alessandro Corsini ◽  
Giovanni Delibra
Keyword(s):  
Total Pressure ◽  
Acoustic Emissions ◽  
Pressure Rise ◽  
Leading Edge ◽  
Cost Effective ◽  
Centrifugal Fan ◽  
Centrifugal Fans ◽  
Flow Features ◽  
Curved Blade ◽  
New Generation

The advancements in fan technology are nowadays animated by two major drivers: the legal requirements that impose minimum fan efficiency grades for fans sold within European Union (and soon US and Asia), and the market request for better air performance and lower sound emissions. Within HVAC (Heating, Ventilating and Air Conditioning) applications, centrifugal fans with forward curved blades are widely used due to the higher total pressure rise capability and lower acoustic emissions with respect to more efficient backward curved blades. However the continuous rise of minimum fan efficiency grades pushes the manufacturers to develop a new generation of forward curved centrifugal fans, improving previous design. Here the challenge is not only on aerodynamics, but in the overall production process, as squirrel cage fans are characterised by a cost-effective consolidated technology, based on simple blade geometries and easy series manufacturing. For example, the blades usually have circular camber lines, as results of cut cylinders. Thus, once the number of blades and the angle at the leading edge are selected, the chord and the deflection capability are constrained as well. These concurring aspects led industry to include in the design process new tools, in particular CFD, to analyse the flow features of the current generation of fans in order to understand which phenomena are to be either controlled or exploited to increase efficiency and total pressure rise. Here we present a numerical investigation on a forward curved blade centrifugal fan for HVAC applications, to highlight the flow features inside the impeller and in the critical region of coupling with the volute. The analysis was carried out with OpenFOAM, an open-source library for CFD. Computations were performed with the frozen rotor approach and validated against available experimental data.

A Numerical Study of the Unsteady Interaction Effects on Diffuser Performance in a Centrifugal Compressor

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
S. Anish ◽  
N. Sitaram ◽  
H. D. Kim
Keyword(s):  
Centrifugal Compressor ◽  
Numerical Study ◽  
Practical Importance ◽  
Leading Edge ◽  
Dominant Frequency ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Unsteady Characteristics ◽  
Cfd Method ◽  
Physical Phenomena

Interaction between rotating impeller and stationary diffuser in a centrifugal compressor is of practical importance in evaluating system performance. The present study aims at investigating how the interaction influences the unsteady diffuser performance and understanding the physical phenomena in the centrifugal compressor. A computational fluid dynamics (CFD) method has been applied to predict the flow field in the compressor, which has a conventional vaned diffuser (VD) and a low solidity vaned diffuser (LSVD). The radial gaps between impeller and diffuser and different flow coefficients are varied. The results obtained show that the major parameter that influences the unsteady variation of diffuser performance is due to the circumferential variation of the flow angle at the diffuser vane leading edge. The physical phenomena behind the pressure recovery variation are identified as the unsteady vortex shedding and the associated energy losses. The vortex core region as well as the shedding of vortices from the diffuser vane are triggered by the variation in the diffuser vane loading, which in turn is influenced by the circumferential variation of the impeller wake region. There is little unsteady variation of flow angle in the span-wise direction. This indicates that the steady state performance characteristics are related to the span-wise variation of flow angle, while the unsteady characteristics are contributed by the circumferential variation of flow angle. At design conditions, dominant frequency components of pressure fluctuation are all periodic and at near stall, these are aperiodic.

Low Noise FEGV Designed by Numerical Method Based on CFD

2004 ◽  
Author(s):  
Naoki Tsuchiya ◽  
Yoshiya Nakamura ◽  
Shinya Goto ◽  
Hidekazu Kodama ◽  
Osamu Nozaki ◽  
...  
Keyword(s):  
Noise Reduction ◽  
Guide Vane ◽  
Three Dimensional ◽  
Leading Edge ◽  
High Amplitude ◽  
Aerodynamic Performance ◽  
Low Noise ◽  
Test Facility ◽  
Noise Sources ◽  
Fan Noise

This paper describes a low noise FEGV (Fan Exit Guide Vane), which is designed by a fan noise prediction method based on CFD. Fan noise is predicted by a hybrid scheme, which is the combination of three-dimensional CFD and three-dimensional linear theory. Characteristics of noise sources are investigated in some kinds of FEGV shapes. High amplitude areas spread not only along the leading edge but also in the span-wise positions along the mid-chord. It is found that high amplitude areas around the mid-chord make an important role in noise generation, and appropriate aft-ward swept angle and span-wise distribution of leaned angle could reduce the amplitude of the noise sources keeping aerodynamic performance. A fan noise test for fan scale models has been conducted at an anechoic test facility in IHI Mizuho to demonstrate noise reduction and performance of low noise FEGV. Noise reduction can be achieved keeping aerodynamic performance compared to conventional straight FEGV.

Numerical and Experimental Study of Impeller Diffuser Interaction

2002 ◽  
Author(s):  
Tarek Mekhail ◽  
Zhaohui Du ◽  
Willem Jansen ◽  
Hanping Chen
Keyword(s):  
Internal Flow ◽  
Leading Edge ◽  
Initial Guess ◽  
Interaction Region ◽  
Centrifugal Fan ◽  
Performance Measurements ◽  
Complex Flow ◽  
Vaned Diffuser ◽  
Flow Phenomena ◽  
Low Efficiency

The unsteadiness of the flow at the leading edge of a vaned diffuser represents a source of low efficiency and instability in a centrifugal turbomachine. Furthermore, the internal flow of the impeller can be affected by asymmetric downstream conditions, which results in extra flow unsteadiness and instabilities. Numerical and experimental data are obtained. The simulation of impeller diffuser interaction is performed using CFX-Tascflow. A frozen rotor simulation is used for the steady calculation and a rotor-stator simulation is used for the unsteady calculation using the steady results as an initial guess. The unsteady simulation is done not only for one impeller and diffuser blades, but also for the whole impeller and diffuser blades using Unix workstation. For the experimental work, a transparent fan is design and tested at The Turbomachinery Laboratory of SJTU. The test rig consists of a centrifugal, shrouded impeller, diffuser and volute casing all made of plexiglass. A particle image velocimeter (PIV) is used to measure the 2-D instantaneous velocity in the interaction region between impeller, vaned. A series of performance measurements were carried out at different speeds. The first trial of measuring the instantaneous flow field in a part of the impeller and vaned diffuser together at different relative locations between them is presented in this work at different flow rates. Obtaining detailed measurements in the interaction region between the impeller and diffuser can help in understanding the complex flow phenomena and improving centrifugal fan and compressor performance. Finally, the comparison between the unsteady measurements and unsteady calculations showed that the Rotor/Stator Model can predict the basic characteristics of unsteady flow in centrifugal fan but still need improvement to satisfy the true transient simulation for unsteady impeller diffuser interaction.

Prediction of the Aerodynamic Noise Generated by a Centrifugal Fan: Numerical Results and Experimental Validation

2006 ◽  
Author(s):  
Rafael Ballesteros-Tajadura ◽  
Sandra Velarde-Sua´rez ◽  
Juan Pablo Hurtado-Cruz ◽  
Bruno Pereiras-Garci´a
Keyword(s):  
Three Dimensional ◽  
Prediction Method ◽  
Numerical Results ◽  
Experimental Results ◽  
Aerodynamic Noise ◽  
Centrifugal Fan ◽  
Fan Noise ◽  
Unsteady Forces ◽  
Model Extension ◽  
Centrifugal Fans

Centrifugal fans are widely used in several applications and, in some cases, the noise generated by these machines has become a serious problem. Usually, the centrifugal fan noise is dominated by tones at the blade passage frequency and its higher harmonics. This is a consequence of the strong interaction between the flow discharged from the impeller and the volute tongue. The purpose of this study is to develop a prediction method for 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 predicts 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. A good agreement has been found between the numerical and the experimental results.

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