Feature extraction of flow and acoustic fields for identification of noise sources and improvement of performance of small axial fans

2020 ◽  
Vol 2020 (0) ◽  
pp. OS07-05
Author(s):  
Wataru OBAYASHI ◽  
Hikaru AONO ◽  
Tomoaki TATSUKAWA ◽  
Kozo FUJII ◽  
Koichi TAKEDA ◽  
...  
Keyword(s):  
Feature Extraction ◽  
Acoustic Fields ◽  
Noise Sources ◽  
Axial Fans

Effect of Rotor-Stator Configuration in the Generation of Vortical Scales and Wake Mixing in Single Stage Axial Fans: Part II — Assessment of Vortex Sound Sources

2013 ◽  
Author(s):  
Mónica Galdo Vega ◽  
Jesus Manuel Fernandez Oro ◽  
Katia María Argüelles Díaz ◽  
Carlos Santolaria Morros
Keyword(s):  
Deep Understanding ◽  
Operating Conditions ◽  
Axial Fan ◽  
Noise Sources ◽  
Sound Sources ◽  
Time Resolved ◽  
Vortex Sound ◽  
Starting Point ◽  
Axial Fans ◽  
The Impact

This second part is devoted to the identification of vortex sound sources in low-speed turbomachinery. As a starting point, the time-resolved evolution of the vortical motions associated to the wake shear layers (reported in the first part of the present study) is employed to obtain vorticity distributions in both blade-to-blade and traverse locations throughout the axial fan stage. Following, the Powell analogy for generation of vortex sound is revisited to obtain the noise sources in the nearfield region of the fan. Both numerical and experimental databases presented previously are now post-processed to achieve a deep understanding of the aeroacoustic behavior of the vortical scales present in the flow. A LES simulation at midspan, using a 2.5D scheme, allows an accurate description of the turn-out time of the shedding vortices, within high-density meshes in the blades and vanes passages, and a correct modeling of the dynamics of turbulence. Besides, thermal anemometry has been employed with a two-wire probe to measure the planar flow in the midspan sections of the fan. Statistical procedures and signal conditioning of velocity traces have confirmed experimentally the unsteady flow patterns devised in the numerical model. The comparison of the rotor-stator and the stator-rotor configurations provides the influence of the wake mixing and the nucleation of turbulent spots in the distribution of the Powell source terms. Moreover, the relation between the turbomachine configuration and the generation of vortex sound can be established, including the impact of the operating conditions and the contributions of the interaction mechanisms.

A Ring Silencer Design for Reducing Noise of Axial Fan

2003 ◽  
Vol 03 (03) ◽  
pp. L259-L264
Author(s):  
Jian-Da Wu ◽  
Mingsian R. Bai
Keyword(s):  
Helmholtz Resonator ◽  
Boundary Region ◽  
Acoustic Analogy ◽  
Axial Fan ◽  
Noise Sources ◽  
Fan Noise ◽  
Fluctuating Pressure ◽  
Axial Fans ◽  
Fan Blade ◽  
Broadband Frequency

In this paper, a ring silencer design for reducing the noise of axial fans is presented. The noise sources on axial fans are usually caused by the fluctuating pressure distribution on the surface of fan blade. Most of the sources are near the trailing edge of blades or boundary region of blades. The ideation of proposed design is based on the principle of Helmholtz resonator for reducing the noise around the fan. The electro-acoustic analogy of this design is presented and simply discussed. Experimental measurement is carried out to evaluate the proposed design for reducing the axial fan noise. The result of experiment indicated that the ring silencer achieved 17 dB in blade passing frequency and 10 dB in other broadband frequency of power spectrum level.

Study of the Coherence of Acoustic Fields of High-Frequency Noise Sources in a Randomly Inhomogeneous Ocean

2018 ◽  
Vol 64 (2) ◽  
pp. 215-224 ◽  
Author(s):  
A. I. Khil’ko ◽  
I. P. Smirnov ◽  
A. I. Mashonin ◽  
A. V. Shafranyuk
Keyword(s):  
High Frequency ◽  
Frequency Noise ◽  
Acoustic Fields ◽  
Noise Sources ◽  
High Frequency Noise

Combined Aerodynamic and Phased Array Microphone Studies on Basic Models of Low-Speed Axial Fan Blade Sections

2018 ◽  
Author(s):  
Esztella Balla ◽  
János Vad
Keyword(s):  
Reynolds Number ◽  
Phased Array ◽  
High Efficiency ◽  
Low Reynolds Number ◽  
Low Noise ◽  
Axial Fan ◽  
Noise Sources ◽  
Low Speed ◽  
Axial Fans ◽  
Low Reynolds

The paper presents comparative aerodynamic and aeroacoustic studies on basic models of blade sections of low-speed, low-Reynolds-number axial fans. The wind tunnel experiments incorporated representative cambered plate and airfoil blade profiles. The aerodynamic measurements revealed that, for low Reynolds numbers, cambered plate blade sections may perform aerodynamically better than airfoil sections. A phased array microphone system, combined with a dipole beamforming and spatial filtering technique, offered a potential for localizing the noise sources in both streamwise and transversal direction. The acoustic studies focused on the profile vortex shedding noise. The results were qualitatively evaluated and compared with the semi-empirical noise prediction model developed by Brooks, Pope, and Marcolini. The measurements are considered as preparation of a dataset contributing to the background for designing high-efficiency, low-noise axial fans operating at low Reynolds number.

Aeroacoustic Analysis of Low-Speed Axial Fans With Different Rotational Speeds in the Design Point

2017 ◽  
Author(s):  
Patrick Buchwald ◽  
Damian M. Vogt ◽  
Julien Grilliat ◽  
Wolfgang Laufer ◽  
Michael B. Schmitz ◽  
...  
Keyword(s):  
Flow Separation ◽  
Rotational Speed ◽  
Numerical Study ◽  
Pressure Rise ◽  
Far Field ◽  
Noise Sources ◽  
Blade Loading ◽  
Design Point ◽  
Low Speed ◽  
Axial Fans

One of the main design decisions in the development of low-speed axial fans is the right choice of the blade loading versus rotational speed, since a target pressure rise could either be achieved with a slow spinning fan and high blade loading or a fast spinning fan with less flow turning in the blade passages. Both the blade loading and the fan speed have an influence on the fan performance and the fan acoustics and there is a need to find the optimum choice in order to maximize efficiency while minimizing noise emissions. The present paper addresses this problem by investigating five different fans with the same pressure rise but different rotational speeds in the design point. In the first part of the numerical study, the fan design is described and steady-state Reynolds-averaged Navier-Stokes (RANS) simulations are conducted in order to identify the performance of the fans in the design point and in off-design conditions. The investigations show the existence of an optimum in rotational speed regarding fan efficiency and identify a flow separation on the hub causing a deflection of the outflow in radial direction as the main loss source for slow spinning fans with high blade loadings. Subsequently, Large Eddy Simulations (LES) along with the acoustic analogy of Ffowcs Williams and Hawkings (FW-H) are performed in the design point to identify the main noise sources and to determine the far-field acoustics. The identification of the noise sources within the fans in the near-field is performed with the help of the power spectral density of the pressure. In the far-field, the sound power level is computed using different parts of the fan surface as FW-H sources. Both methods show the same trends regarding noise emissions and allow for a localization of the noise sources. The flow separation on the hub is one of the main noise sources along with the tip vortex with an increase in its strength towards lower rotational speeds and higher loading. Furthermore, a horseshoe vortex detaching from the rotor leading edge and impinging on the pressure side as well as the turbulent boundary layer on the suction side represent significant noise sources. In the present investigation, the maximum in efficiency coincides with the minimum in noise emissions.

scholarly journals A Feature Extraction Method for Vibration Signal of Bearing Incipient Degradation

2016 ◽  
Vol 16 (3) ◽  
pp. 149-159 ◽  
Author(s):  
Haifeng Huang ◽  
Huajiang Ouyang ◽  
Hongli Gao ◽  
Liang Guo ◽  
Dan Li ◽  
...  
Keyword(s):  
Feature Extraction ◽  
Extraction Method ◽  
Signal To Noise Ratio ◽  
Experimental Studies ◽  
Vibration Signal ◽  
Noise Sources ◽  
Rolling Bearings ◽  
Vibration Signals ◽  
Feature Extraction Method ◽  
Spectral Kurtosis

Abstract Detection of incipient degradation demands extracting sensitive features accurately when signal-to-noise ratio (SNR) is very poor, which appears in most industrial environments. Vibration signals of rolling bearings are widely used for bearing fault diagnosis. In this paper, we propose a feature extraction method that combines Blind Source Separation (BSS) and Spectral Kurtosis (SK) to separate independent noise sources. Normal, and incipient fault signals from vibration tests of rolling bearings are processed. We studied 16 groups of vibration signals (which all display an increase in kurtosis) of incipient degradation after they are processed by a BSS filter. Compared with conventional kurtosis, theoretical studies of SK trends show that the SK levels vary with frequencies and some experimental studies show that SK trends of measured vibration signals of bearings vary with the amount and level of impulses in both vibration and noise signals due to bearing faults. It is found that the peak values of SK increase when vibration signals of incipient faults are processed by a BSS filter. This pre-processing by a BSS filter makes SK more sensitive to impulses caused by performance degradation of bearings.

scholarly journals REDUCING THE NOISE INTENSITY OF SUBSONIC TURBULENT JETS USING NOISE-ATTENUATING DEVICES

Akustika ◽  
2019 ◽  
Vol 32 ◽  
pp. 73-78
Author(s):  
Oleg Sitknikov ◽  
Pavel Nakoryakov ◽  
Margarita Mironova ◽  
Ksenia Valeeva
Keyword(s):  
Noise Intensity ◽  
Turbulent Jets ◽  
Aircraft Noise ◽  
Acoustic Fields ◽  
Noise Sources ◽  
Acoustic Characteristics ◽  
Research Results

Reducing aircraft noise is a pressing issue. To solve it, information is needed on the parameters of the acoustic fields of noise sources. A study was made of the acoustic characteristics of models of noise-attenuating devices. Analysis of the research results revealed the design of the noise-attenuating device with the greatest effect. Based on the results of the research, a noise-attenuating device for the «Ansat» helicopter was developed. The proposed measures to reduce the acoustic pulsations of the engines of a light helicopter.

Effects of Vortex Generating Tabs on Noise Sources in an Ideally Expanded Mach 1.3 Jet

2003 ◽  
Vol 2 (1) ◽  
pp. 35-63 ◽  
Author(s):  
J. Hileman ◽  
M. Samimy
Keyword(s):  
Flow Visualization ◽  
Microphone Array ◽  
Pressure Ratio ◽  
Mixing Layer ◽  
Power Spectra ◽  
Acoustic Fields ◽  
Streamwise Vortices ◽  
Noise Sources ◽  
Noise Measurements ◽  
Generation Mechanisms

The flow and acoustic fields of an ideally expanded Mach 1.3 axisymmetric jet with delta tabs were examined to explore the effects of the tabs on noise sources. This work continues research that was performed on a baseline (no-tab) jet. Noise measurements were made at an angle of 30° to the downstream jet axis to allow a direct comparison to previous work, and to relate the sound generation mechanisms to the large structures that were visualized with temporally resolved flow visualization. Additional acoustic measurements were made at 60° and 90° locations. Three cases were examined: a baseline jet, a single delta tab jet, and a dual delta tab jet. Both tab jets were operated at the same pressure ratio as the baseline jet, which was ideally expanded. Power spectra and average acoustic waveform measurements were made for a variety of azimuthal locations; apparent noise origins were estimated with a 3-D microphone array; and temporally resolved flow visualization was used to examine the dynamic flow structure of the jet's mixing-layer. The results confirm that the tabs generate strong streamwise vortices that have a significant effect on both the flow and acoustic fields of the jet. The tabs cause significant deformation in the cross-stream plane of the mixing-layer, as well as regulating the formation and roll-up of vortices due to Kelvin Helmholtz instability. With the addition of tabs, the noise field becomes azimuthally dependent and the region of noise generation moves dramatically upstream. It appears that the tabs are directly responsible for an increase in noise over a range of Strouhal numbers between 0.8 and 2.5 through generated streamwise vortices and they are indirectly responsible for the modification of the noise generating mechanisms at Strouhal numbers below 0.6 through the induced spanwise vortex roll-ups.

scholarly journals Localization and characterization of rotating noise sources on axial fans by means of an irregularly shaped microphone array

2021 ◽  
Vol 1909 (1) ◽  
pp. 012003
Author(s):  
O Amoiridis ◽  
R Zamponi ◽  
A Zarri ◽  
J Christophe ◽  
C Schram
Keyword(s):  
Microphone Array ◽  
Noise Sources ◽  
Axial Fans
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