Near‐ultrasound, broadband noise generated by low‐speed airflow over wires.

2010 ◽  
Vol 127 (3) ◽  
pp. 1781-1781
Author(s):  
W.C. Kirkpatrick Alberts ◽  
Kevin J. Sanchez ◽  
Mark A. Coleman ◽  
Josh Gabrielse ◽  
David A. Ligon
Keyword(s):  
Broadband Noise ◽  
Low Speed

scholarly journals Suppression of broadband noise radiated by a low-speed fan in a duct

2010 ◽  
Vol 128 (1) ◽  
pp. 152-163 ◽  
Author(s):  
L. Huang ◽  
X. Ma ◽  
L. G. Feng
Keyword(s):  
Broadband Noise ◽  
Low Speed

Comparison between Measurements and Predictions of Fan Broadband Noise on a Low Speed Fan Rig

2010 ◽  
Vol 9 (3) ◽  
pp. 237-251 ◽  
Author(s):  
V. Jurdic ◽  
P. Joseph ◽  
A. Moreau ◽  
L. Enghardt
Keyword(s):  
Broadband Noise ◽  
Low Speed

Numerical Analysis of an Industrial Fan Fitted With Noise Reduction Devices

2006 ◽  
Author(s):  
J. Amaral Teixeira ◽  
E. Naylor ◽  
P. C. Ivey ◽  
A. G. Sheard ◽  
I. R. Kinghorn
Keyword(s):  
Numerical Analysis ◽  
Noise Reduction ◽  
Flow Characteristics ◽  
Pressure Rise ◽  
Broadband Noise ◽  
Noise Sources ◽  
Fan Noise ◽  
Trailing Edge ◽  
Low Speed ◽  
The Individual

The reduction of noise emitted by industrial low speed cooling fans, particularly those fitted to air conditioning systems is a concern to fan manufacturers. The market for industrial low speed fans is highly competitive, with fan noise being the major differentiating factor between competing products. Noise reduction strategies are therefore implemented but these can adversely affect the fan’s pressure delivery capability. A reduction of fan speed can also lead to a reduction in fan noise but this is usually accompanied by a corresponding reduction in pressure rise and flow rate. The practical difficulties associated with maintaining fan pressure and flow characteristics while simultaneously reducing fan noise present fan manufacturers with a challenge. Traditional empirical approaches to the reduction of fan noise have almost been exhausted and no longer offer the potential to significantly reduce fan noise. The understanding of the aerodynamic mechanisms that act as broadband noise sources in low speed fans has been the subject of a considerable number of papers over many years. For most fans operating as a single blade row, the main sources of noise, other than those dependent on the incident turbulence levels, depend on the trailing edge and tip gap flow conditions. A range of strategies seeking to control the noise generated by these regions have been proposed over time by various authors and a number of these schemes have reached production status. The current paper details the numerical analysis of an industrial low speed fan, commonly used in conjunction with a cooling matrix, and which incorporates two distinct noise reduction features; trailing edge crenulations and a blade tip fence. Comparisons are carried out between various combinations of blades, with and without the individual features, and a discussion of the aerodynamics of the particular configurations is undertaken from a perspective of their noise reduction capabilities.

Investigation on the Influence of Mesh Topology and Freestream Turbulence Intensity in Broadband Noise Prediction of Axial Fans

2014 ◽  
Author(s):  
A. Zanon ◽  
M. De Gennaro ◽  
H. Kuehnelt ◽  
D. Langmayr ◽  
D. Caridi
Keyword(s):  
Experimental Data ◽  
Broadband Noise ◽  
Computational Time ◽  
Noise Prediction ◽  
Hybrid Mesh ◽  
Low Speed ◽  
Mesh Topology ◽  
Inflow Turbulence ◽  
Axial Fans ◽  
The Impact

Aerodynamic noise prediction is a major challenge in computational aeroacoustics due to the complexity of phenomena involved such as turbulence and laminar to turbulent transition. Accurate numerical methodologies, capable to provide reliable predictions in a reasonable computational time, are of large interest for the industrial design of Heating, Ventilation and Air-Conditioning (HVAC) systems. The objective of the present research work is to benchmark different CFD/CAA simulation setup (i.e. mesh topologies, boundary conditions) for predicting the broadband noise generated by low speed axial fans to develop guidelines for reliable and computationally affordable simulation. In previous works the authors investigated the capabilities of the Zonal LES technique coupled with the Ffowcs Williams-Hawkings acoustic analogy for the prediction of the noise generated by an unducted low speed axial fan. The results showed a good agreement with aerodynamic and aeroacoustic experimental data. Despite the achievements obtained so far, the high physical and numerical complexity of the problem calls for further investigations. The latest developments, presented here, focus on the impact of the mesh topology and the inflow turbulence on the far field noise prediction. Two computational meshes with different topology are investigated: an unstructured-hybrid mesh, which can be generated with fast and highly automated methods, and a structured-hybrid mesh, which allows better control of the volume mesh around the blade. Both meshes are designed to adequately resolve the boundary layer, providing LES driven values of y+, x+ and z+ on the blade surface for the operating condition considered. Two different levels of inflow turbulence are studied, one representing an ideal turbulence-free unbounded environment, and one mimicking the experimental measurements environment. All the aerodynamic and aeroacoustic simulation results presented are benchmarked with experimental data acquired by the authors.

scholarly journals Noise generation by turbulence–propeller interaction in asymmetric flow

2014 ◽  
Vol 758 ◽  
pp. 121-149 ◽  
Author(s):  
Rosalyn A. V. Robison ◽  
N. Peake
Keyword(s):  
Axisymmetric Flow ◽  
Broadband Noise ◽  
Asymmetric Flow ◽  
Low Speed ◽  
Static Testing ◽  
Flight Direction ◽  
Flow Features ◽  
Significant Extension ◽  
Radiated Sound ◽  
Asymmetric Distortion

AbstractThis paper is concerned with a particular source of both broadband and tonal aeroengine noise, termed unsteady distortion noise. This noise arises from the interaction between turbulent eddies, which occur naturally in the atmosphere or are shed from the fuselage, and the rotor. This interaction produces broadband noise across a broad frequency spectrum. In cases in which there is strong streamtube contraction, which is especially true for open rotors at low-speed conditions (such as at take-off or for static testing), tonal noise at frequencies equal to multiples of the blade passing frequency are also produced, owing to the enhanced axial coherence caused by eddy stretching. In a previous paper (Majumdar & Peake, J. Fluid Mech., vol. 359, 1998, pp. 181–216), a model for unsteady distortion noise was developed in axisymmetric flow. However, asymmetric situations are also of much interest, and in this paper we consider two cases of asymmetric distortion: firstly that induced by the proximity of a second rotor, and secondly that caused by non-zero inclination to the flight direction, as found at take-off. This requires significant extension of the previous axisymmetric analysis. We find that the introduction of asymmetric flow features can have a significant decibel effect on the radiated sound power. For instance, in low-speed conditions we find that the tonal level is reduced significantly by the proximity of a second rotor, compared to the axisymmetric case, while the effect on the broadband levels is rather modest.

Optimised Test Rig for Measurements of Aerodynamic and Aeroacoustic Performance of Leading Edge Serrations in Low-Speed Fan Application

2018 ◽  
Author(s):  
Till M. Biedermann ◽  
F. Kameier ◽  
C. O. Paschereit
Keyword(s):  
Noise Reduction ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Broadband Noise ◽  
Test Rig ◽  
Low Speed ◽  
Turbulent Inflow ◽  
Inflow Turbulence ◽  
Leading Edges ◽  
Inflow Conditions

With the aim of analysing the efficiency of leading edge serrations under realistic conditions, an experimental rig was developed where a ducted low-speed fan is installed that allows to gather data of both, aerodynamic and aeroacoustic nature. Turbulent inflow conditions were generated via biplane-square grids, resulting in turbulence intensities of different magnitude and of high isotropic character that were quantified by use of hotwire measurements. The fan blades were designed according to the NACA65(12)-10 profile with interchangeable features and an independently adjustable angle of attack. Altogether, five different parameters can be analysed, namely the serration amplitude and wavelength, the angle of attack, the inflow turbulence and the rotational speed. In addition, the blade design allows for a variation of the blade skew, sweep and dihedral as well. The presented work focusses on validating and optimising the test rig as well as a detailed quantification of the turbulent inflow conditions. Furthermore, first aerodynamic and aeroacoustic results of fan blades with straight leading edges are compared to those of serrated leading edges. The aerodynamic performance was found to be mainly affected by the serrations as a function of the serration amplitude. Aeroacoustically, a clear sensitivity towards different incoming turbulence intensities and serration parameters was detected, showing significant broadband noise reduction below 2 kHz with an overall noise reduction of ΔOASPL = 3.4 dB at maximum serration amplitudes and minimum wavelengths.

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