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.

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.

scholarly journals Experimental Characterisation of the Far-Field Noise in Axial Fans Fitted with Shaped Tip End-Plates

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
S. Bianchi ◽  
A. Corsini ◽  
A. G. Sheard
Keyword(s):  
Vortex Breakdown ◽  
Vortex Formation ◽  
Broadband Noise ◽  
Sound Power ◽  
Far Field ◽  
Tip Leakage Flow ◽  
Noise Sources ◽  
End Plate ◽  
Field Noise ◽  
Flow Vortex

The authors investigate the far-field noise emissions of a datum fan blade fitted with tip end-plate geometries, originally designed to control the leakage vortex swirl level. The end-plate geometries influence the tip-leakage flow, vortex formation, and swirl level. In doing so, the end-plate geometries influence the sound-power levels. After an evaluation of fan rotors' aerodynamic performance, the study compares the rotors' far-field noise signature characterised in terms of sound-power and pressure-level spectra to enable and assess the end-plate acoustic pay-off. The investigation attempts to establish a cause-and-effect relationship between the tip-flow dynamics and the radiated sound fields, exploring the diverse directivity patterns. The authors found a tonal reduction, due to the enhanced blade-tip end-plates and clarified the relevance of the tip features influencing the radial distribution of the noise sources using coherence analysis. The modified multiple-vortex breakdown end-plate design was effective in reducing the broadband noise, giving an improvement in the frequency range of the turbulent noise.

Surface pressure fluctuations on aircraft flaps and their correlation with far-field noise

2000 ◽  
Vol 415 ◽  
pp. 175-202 ◽  
Author(s):  
Y. P. GUO ◽  
M. C. JOSHI ◽  
P. H. BENT ◽  
K. J. YAMAMOTO
Keyword(s):  
Surface Pressure ◽  
Near Field ◽  
Pressure Fluctuations ◽  
Dominant Frequency ◽  
Vortex Structures ◽  
Far Field ◽  
Mean Flow ◽  
Noise Sources ◽  
Side Edge ◽  
Field Noise

This paper discusses unsteady surface pressures on aircraft flaps and their correlation with far-field noise. Analyses are made of data from a 4.7% DC-10 aircraft model test, conducted in the 40 × 80 feet wind tunnel at NASA Ames Research Center. Results for various slat/wing/flap configurations and various flow conditions are discussed in detail to reveal major trends in surface pressure fluctuations. Spectral analysis, including cross-correlation/coherence, both among unsteady surface pressures and between far-field noise and near-field fluctuations, is used to reveal the most coherent motions in the near field and identify potential sources of noise related to flap flows. Dependencies of surface pressure fluctuations on mean flow Mach numbers, flap settings and slat angles are discussed. Dominant flow features in flap side edge regions, such as the formation of double-vortex structures, are shown to manifest themselves in the unsteady surface pressures as a series of spectral humps. The spectral humps are shown to correlate well with the radiated noise, indicating the existence of major noise sources in flap side edge regions. Strouhal number scaling is used to collapse the data with satisfactory results. The effects of flap side edge fences on surface pressures are also discussed. It is shown that the application of fences effectively increases the thickness of the flaps so that the double-vortex structures have more time to evolve. As a result, the characteristic timescale of the unsteady sources increases, which in turn leads to a decrease in the dominant frequency of the source process. Based on this, an explanation is proposed for the noise reduction mechanism of flap side edge fences.

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 Similarity scaling of jet noise sources for low-order jet noise modelling based on the Goldstein generalised acoustic analogy

2017 ◽  
Vol 16 (6) ◽  
pp. 476-490 ◽  
Author(s):  
Vasily A Semiletov ◽  
Sergey A Karabasov
Keyword(s):  
Jet Noise ◽  
Field Measurements ◽  
Noise Prediction ◽  
Far Field ◽  
Acoustic Analogy ◽  
Noise Sources ◽  
Modelling Framework ◽  
Noise Data ◽  
Field Noise ◽  
Low Order

As a first step towards a robust low-order modelling framework that is free from either calibration parameters based on the far-field noise data or any assumptions about the noise source structure, a new low-order noise prediction scheme is implemented. The scheme is based on the Goldstein generalised acoustic analogy and uses the Large Eddy Simulation database of fluctuating Reynolds stress fields from the CABARET MILES solution of Semiletov et al. corresponding to a static isothermal jet from the SILOET experiment for reconstruction of effective noise sources. The sources are scaled in accordance with the physics-based arguments and the corresponding sound meanflow propagation problem is solved using a frequency domain Green’s function method for each jet case. Results of the far-field noise predictions of the new method are validated for the two NASA SHJAR jet cases, sp07 and sp03 from and compared with the reference predictions, which are obtained by applying the Lighthill acoustic analogy scaling for the SILOET far-field measurements and using an empirical jet-noise prediction code, sJet.

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.

Aerodynamic Far Field Noise in Idling Circular Sawblades

1984 ◽  
Vol 106 (3) ◽  
pp. 441-446 ◽  
Author(s):  
C. D. Mote ◽  
Wen Hua Zhu
Keyword(s):  
Sound Pressure ◽  
Acoustic Pressure ◽  
Dipole Source ◽  
Radial Coordinate ◽  
Far Field ◽  
Field Noise ◽  
Dipole Sources

The acoustic pressure radiated to the far field from dipole sources at the rim of a rotating circular sawblade is investigated theoretically and experimentally. Scattering from the sawblade surfaces and the presence of dipole source components in both the normal and radial coordinate directions explain the observed directivity and the dependence of the sound pressure upon sawblade rim velocity.

scholarly journals Jet-Surface Interaction Test: Far-Field Noise Results

2012 ◽  
Author(s):  
Clifford Brown
Keyword(s):  
Jet Noise ◽  
Surface Interaction ◽  
Shielding Effect ◽  
Noise Prediction ◽  
Far Field ◽  
Noise Sources ◽  
Trailing Edge ◽  
Wide Range ◽  
Field Noise ◽  
Interaction Test

Many configurations proposed for the next generation of aircraft rely on the wing or other aircraft surfaces to shield the engine noise from the observers on the ground. However, the ability to predict the shielding effect and any new noise sources that arise from the high-speed jet flow interacting with a hard surface is currently limited. Furthermore, quality experimental data from jets with surfaces nearby suitable for developing and validating noise prediction methods are usually tied to a particular vehicle concept and, therefore, very complicated. The Jet/Surface Interaction Test was intended to supply a high quality set of data covering a wide range of surface geometries and positions and jet flows to researchers developing aircraft noise prediction tools. During phase one, the goal was to measure the noise of a jet near a simple planar surface while varying the surface length and location in order to: (1) validate noise prediction schemes when the surface is acting only as a jet noise shield and when the jet/surface interaction is creating additional noise, and (2) determine regions of interest for more detailed tests in phase two. To meet these phase one objectives, a flat plate was mounted on a two-axis traverse in two distinct configurations: (1) as a shield between the jet and the observer (microphone array) and (2) as a reflecting surface on the opposite side of the jet from the observer. The surface was moved through axial positions 2 ≤ xTE/Dj ≤ 20 (measured at the surface trailing edge, xTE, and normalized by the jet diameter, Dj) and radial positions 1 ≤ h/Dj ≤ 20. Far-field and phased array noise data were acquired at each combination of axial and radial surface location using two nozzles and at 8 different jet exit conditions across several flow regimes (subsonic cold, subsonic hot, underexpanded, ideally expanded, and overexpanded supersonic cold). The far-field noise results, discussed here, show where the surface shields some of the jet noise and, depending on the location of the surface and the observer, where scrubbing and trailing edge noise sources are created as a surface extends downstream and approaches the jet plume.

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.

Surface Coating Effect on Protection of Icing for Axial Fan Blade

2011 ◽  
Author(s):  
Takeshi Murooka ◽  
Shinichirou Shishido ◽  
Riho Hiramoto ◽  
Takakazu Minoya
Keyword(s):  
Surface Coating ◽  
Axial Fan ◽  
Fan Blade
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