scholarly journals Investigations on noise sources on a contra-rotating axial fan with different modifications

2019 ◽  
Vol 111 ◽  
pp. 02076 ◽  
Author(s):  
Ralph Krause ◽  
Christian Friebe ◽  
Michael Kerscher ◽  
Christof Puhle
Keyword(s):  
Axial Fan ◽  
Noise Sources ◽  
Trailing Edge ◽  
Sound Sources ◽  
Rotating Blades ◽  
First Results ◽  
Fan Blade ◽  
Future Work ◽  
Different Sources ◽  
Beamforming Algorithm

An Acoustic Camera was applied to examine modifications of fan blade designs regarding their noise emissions. A so-called rotational beamforming algorithm allows for the detection of sound sources on the rotating blades by using a virtual rotation of the microphones. Depending upon the frequency different sources could be localized. Both the leading and the trailing edge were modified. This paper shows the performed modifications and tests with the Acoustic Camera. It also presents first results and gives an outlook on future work.

Trailing-edge noise reduction of a wing by a surface modification

2021 ◽  
Vol 263 (3) ◽  
pp. 3194-3201
Author(s):  
Varun Bharadwaj Ananthan ◽  
R.A.D. Akkermans ◽  
Dragan Kozulovic
Keyword(s):  
Noise Reduction ◽  
Stochastic Approach ◽  
Slight Reduction ◽  
Noise Sources ◽  
Trailing Edge ◽  
Sound Sources ◽  
Airframe Noise ◽  
Trailing Edge Noise ◽  
Random Particle ◽  
Noise Production

There is an increased emphasis on reducing airframe noise in the last decades. Airframe noise is sound generated by the interaction of a turbulent flow with the aircraft geometry, and significantly contributes to the overall noise production during the landing phase. One examples of airframe noise is the noise generated at a wing's trailing edge, i.e., trailing-edge noise. In this contribution, we numerically explore the local application of riblets for the purpose of trailing-edge noise reduction. Two configurations are studied: i) a clean NACA0012 wing section as a reference, and ii) the same configuration with riblets installed at the wing's aft part. The numerical investigation follows a hybrid computational aeroacoustics approach, where the time-average flow is studied by means of RANS. Noise sources are generated by means of a stochastic approach called Fast Random Particle Mesh method. The results show a deceleration of the flow behind the riblets. Furthermore, the turbulent kinetic energy indicates increased unsteadiness behind the riblets which is shifted away from the wall due to the presence of the riblets. Lastly, the sound sources are investigated by means of the 3D Lamb-vector, which indicates a slight reduction in magnitude near the trailing edge.

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.

Reduced order model analysis to identify possible aerodynamic noise sources of small axial fan: POD and CNN

2021 ◽  
Vol 263 (3) ◽  
pp. 3748-3755
Author(s):  
Wataru Obayashi ◽  
H. Aono ◽  
T. Tatsukawa ◽  
K. Fujii ◽  
K. Takemi
Keyword(s):  
Cooling System ◽  
Model Analysis ◽  
Reduced Order Model ◽  
Aerodynamic Noise ◽  
Air Cooling ◽  
Axial Fan ◽  
Order Model ◽  
Noise Sources ◽  
Sound Sources ◽  
Reduced Order

This paper reports computational analysis of location and strength of sound source of the noise generated by a small axial fan widely used as an air-cooling system. High-fidelity Navier-Stokes simulations with high-resolution compact scheme are conducted with an implicit Large Eddy Simulation (LES) method on a HPC system and the resultant large-scale data confirms existence of unsteady vortex structures and their interactions around the impellers, boss and casing of the fan. To identify location and strength of the sound sources, reduced order model analysis is conducted for the distribution of pressure fluctuations in space and time. Snapshot POD (Proper Orthogonal Decomposition) analysis both in time and in circumferential direction, together with conventional FFT analysis, identifies location and strength of the sound sources. In addition, Convolutional Neural Network (CNN) is attempted, which shows more physical mode decomposition and separates some of the important features shown in the snapshot POD analysis. The study shows that the two data-mining techniques considered here identify possible aerodynamic noise sources of the axial fan clearly in comparison to those in the previous studies.

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.

Experimental Study of the Effect of Serrations on Axial Flow Fan Blade Trailing Edge

2016 ◽  
Author(s):  
Dhyanjyoti Deb Nath ◽  
K. Viswanath ◽  
Ankit Bhai Patel
Keyword(s):  
Axial Velocity ◽  
Pressure Sensors ◽  
Tangential Velocity ◽  
Axial Flow ◽  
Experimental Investigations ◽  
Spanwise Direction ◽  
Axial Fan ◽  
Trailing Edge ◽  
Trailing Edges ◽  
Fan Blade

Rotor wakes shed from a compressor rotor impinge on downstream blades and is a major source of rotor-stator interaction noise and much research has been dedicated on wake attenuation. Serrated trailing edges is one such wake attenuation technique where the vortices produced at the serrated trailing edges enhance mixing and create a more uniform flow at stator inlet. The present paper investigates the effect of serrations on the trailing edge of a forced vortex axial fan blade. Experimental investigations were carried out at rotor outlet using pneumatic probes and fast response pressure sensors. It is found that total and static pressures reduce in serrated blades due to reduced turning and hence reduced work input. The absolute tangential velocity wake deficit decreases in serration valleys and improvement in axial velocity wake deficit is also found. Improvements as large as 19% and 18% decrease in absolute tangential velocity and axial velocity wake deficit are found at certain radii. The spanwise shape of the wake is altered by the serrations and a wake pattern undulating in the spanwise direction is observed. These are expected to bring down the circumferential variation of the velocity and its phase before entering the next row of blades and bring down the tonal noise.

scholarly journals Trailing edge noise theory for rotating blades in uniform flow

2013 ◽  
Vol 469 (2157) ◽  
pp. 20130065 ◽  
Author(s):  
S. Sinayoko ◽  
M. Kingan ◽  
A. Agarwal
Keyword(s):  
Angular Frequency ◽  
Rotational Frequency ◽  
Mean Flow ◽  
Noise Sources ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Rotating Blades ◽  
Noise Radiation ◽  
Cooling Fan ◽  
New Formulation

This paper presents a new formulation for trailing edge noise radiation from rotating blades based on an analytical solution of the convective wave equation. It accounts for distributed loading and the effect of mean flow and spanwise wavenumber. A commonly used theory due to Schlinker and Amiet predicts trailing edge noise radiation from rotating blades. However, different versions of the theory exist; it is not known which version is the correct one, and what the range of validity of the theory is. This paper addresses both questions by deriving Schlinker and Amiet's theory in a simple way and by comparing it with the new formulation, using model blade elements representative of a wind turbine, a cooling fan and an aircraft propeller. The correct form of Schlinker and Amiet's theory is identified. It is valid at high enough frequency, i.e. for a Helmholtz number relative to chord greater than one and a rotational frequency much smaller than the angular frequency of the noise sources.

scholarly journals Comparison of beamforming algorithms based on localization of calibrating sound sources and air jet noise

2018 ◽  
Vol 7 (2.23) ◽  
pp. 119 ◽  
Author(s):  
V Ershov ◽  
V V. Palchikovskiy
Keyword(s):  
Microphone Array ◽  
Jet Noise ◽  
Point Sources ◽  
Good Work ◽  
Noise Sources ◽  
Sound Sources ◽  
Air Jet ◽  
Good Ability ◽  
Static Point ◽  
Beamforming Algorithm

The paper considers study of beamforming algorithms for localization of noise sources. The mathematical formulations are briefly described for the following algorithms: Delay-and-Sum Beamforming, Cross-spectral Beamforming, Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS). Based on the mentioned algorithms the program codes were developed. Operability of the program codes was tested on virtual localization of the point sources. All algorithms demonstrated good ability to distinguish these sources at different frequencies at their close position relative to each other. Initially, experiments were based on localization of calibrating static sound sources (beepers) using Bruel & Kjaer 54-microphone array. The measured data were processed both in the Bruel & Kjaer software and in the developed software. For static point sources, all algorithms have shown good work quality. The experiments were also carried out for the localization of noise sources in a turbulent air jet. In this case, the best results were demonstrated by Cross-Spectral Beamforming algorithm.  

Computation of Turbulent Flows and Aero-Acoustics From an Axial Fan

2002 ◽  
Author(s):  
Il-Sung Bae ◽  
Hooi-Joong Kim ◽  
Seungbae Lee
Keyword(s):  
Turbulent Flows ◽  
Dipole Source ◽  
Spanwise Direction ◽  
Far Field ◽  
Axial Fan ◽  
Noise Sources ◽  
Lift Forces ◽  
Fan Blade ◽  
Drag And Lift ◽  
Field Noise

LES formulation was applied to simulate the flow fields around rotating fan blades tested by DLR. The turbulent flows around fan blade rotating with 500 RPM were simulated and the far-field noise was exactly computed by using the Ffowcs Williams and Hawkings equation with an inclusion of quadrupole source formulation. Variations of lift forces and deviation angles in the spanwise direction were analyzed to correlate flow parameters with acoustics parameters and identify noise sources. The dipole noise computed at the far-field by computed drag and lift forces was in good agreement with experimental data and the dipole source was also found to be the major contributor to overall far-field noise from unsteady calculation.

Noise source location and scaling of subsonic upper-surface blowing

2020 ◽  
Vol 19 (3-5) ◽  
pp. 191-206
Author(s):  
Trae L Jennette ◽  
Krish K Ahuja
Keyword(s):  
Strouhal Number ◽  
Noise Source ◽  
Low Frequency ◽  
Directivity Pattern ◽  
Source Location ◽  
Dipole Source ◽  
Frequency Noise ◽  
Noise Sources ◽  
Trailing Edge ◽  
Trailing Edge Noise

This paper deals with the topic of upper surface blowing noise. Using a model-scale rectangular nozzle of an aspect ratio of 10 and a sharp trailing edge, detailed noise contours were acquired with and without a subsonic jet blowing over a flat surface to determine the noise source location as a function of frequency. Additionally, velocity scaling of the upper surface blowing noise was carried out. It was found that the upper surface blowing increases the noise significantly. This is a result of both the trailing edge noise and turbulence downstream of the trailing edge, referred to as wake noise in the paper. It was found that low-frequency noise with a peak Strouhal number of 0.02 originates from the trailing edge whereas the high-frequency noise with the peak in the vicinity of Strouhal number of 0.2 originates near the nozzle exit. Low frequency (low Strouhal number) follows a velocity scaling corresponding to a dipole source where as the high Strouhal numbers as quadrupole sources. The culmination of these two effects is a cardioid-shaped directivity pattern. On the shielded side, the most dominant noise sources were at the trailing edge and in the near wake. The trailing edge mounting geometry also created anomalous acoustic diffraction indicating that not only is the geometry of the edge itself important, but also all geometry near the trailing edge.

scholarly journals Endoscopic Pan/Tilt Camera for Thorax Interventions – Design and first results

2019 ◽  
Vol 5 (1) ◽  
pp. 517-519
Author(s):  
Alexander Mrokon ◽  
Peter P. Pott ◽  
Volker Steger
Keyword(s):  
Minimally Invasive ◽  
Inclination Angle ◽  
Magnetic Circuit ◽  
Mechanical Stability ◽  
Fem Simulation ◽  
Camera System ◽  
Design Changes ◽  
First Results ◽  
Set Up ◽  
Future Work

AbstractMinimally invasive surgery in some cases suffers from a limited view because certain areas are obscured by others. In this paper, a system is described, which can be used in minimally invasive procedures as an addition to a standard endoscope to improve the range of view. Through FEM simulation a magnetic circuit was designed to position the camera head. Subsequently, a camera positioning system was set up that includes an extracorporeal and an intracorporeal unit. The first controls the intracorporeal system. The latter has a camera inclination angle of up to 65° and an additional vertically downward viewing angle when aligned in parallel (inclination angle 0°). The panning angle is 360°. The camera system was evaluated in lab and cadaver trials. It has been found that the size of the intracorporeal system (16 × 10 × 150 mm) represents a major problem. Future work will focus of the reduction of the system’s size, the improvement of the camera image quality, and design changes considering mechanical stability.

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