Cross Wind Influence on Noise Emission and Computed Vibrational Noise of an Axial Fan

2015 ◽  
Author(s):  
Till Heinemann ◽  
Sven Münsterjohann ◽  
Florian Zenger ◽  
Stefan Becker
Keyword(s):  
Wind Tunnel ◽  
Flow Field ◽  
Laser Scanning ◽  
Sound Pressure ◽  
Cross Flow ◽  
Test Rig ◽  
Axial Fan ◽  
Noise Emission ◽  
Axial Fans ◽  
Operating Points

The total noise emissions of two commercial axial fans were measured in a semi-anechoic fan test rig in comparison. The total sound pressure levels and the respective spectra were found to change with the fans’ operating points. Increasing fan flow rates lowered the total acoustic pressure, with a broadband shift towards higher frequencies, keeping perceived (A-weighted) sound pressure levels approximately constant over a wide range of operating points. In a second step, Laser Scanning Vibrometry measurements of the fan blades’ axial motion were conducted in comparison inside a wind tunnel fan test rig. Rotating blade surface vibration data was used as sole input to a Ffowcs Williams and Hawkings algorithm, to estimate noise emission from vibration. The computed noise from surface vibration was found to be hardly affected by the change of fan flow rate. In the application of an axial fan subject to natural wind or induced cross flow at its inlet, the flow field and possible noise emission of the fan changes. Microphone measurements of the cross flow influence inside a semi-anechoic wind tunnel revealed increasing broadband noise with ambient flow field velocity, and an amplification of the sound at the blade passing frequency harmonics. Similar excitations of the blade passing frequency harmonics under cross flow influence were also found in sound pressure spectra computations based on the Laser Scanning Vibrometry measurement data captured in the wind tunnel fan test rig. Blade vibration is considered to contribute to the low frequency tonal noise emission of axial fans operating under cross flow conditions.

Experimental Investigation of Ambient Wind Influence on the Performance of Axial Fans

2014 ◽  
Author(s):  
Till Heinemann ◽  
Stefan Becker
Keyword(s):  
Wind Tunnel ◽  
Operating Mode ◽  
Positive Influence ◽  
Test Rig ◽  
Axial Fan ◽  
Axial Fans ◽  
Wind Velocities ◽  
Wind Influence ◽  
Water Scarce ◽  
The University

The EU-funded MACCSol project is developing a new modular air-cooled condenser design for power plant applications in water scarce regions. In that scope, this work is to examine the influence ambient winds may have on an axial ventilator’s performance. An axial fan test rig was built inside a wind tunnel environment at the University of Erlangen to realize different wind velocities and angles. Total fan pressure was captured using an array of 81 Kiel probes. The validity of the test rig adaptations to the wind tunnel restrictions was shown in comparison to results from ISO 5801 standard fan test rigs. Two different fan geometries were examined in their characteristic fan curves’ reactions to wind influence at the free fan inlet. The two fans’ characteristic curves showed effects differing in magnitude, but similar in their tendency. While frontal winds tended to improve fan performance, cross winds reduced it. In reverse operating mode, the effect of wind at the fan outlet demonstrated little but positive influence on the fan curve. In order to reduce negative cross wind influence at the fan inlet, different conical and cylindrical inlet extensions were tested. Short conical shrouds performed best.

scholarly journals Axial Fan Performance under the Influence of a Uniform Ambient Flow Field

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Till Heinemann ◽  
Stefan Becker
Keyword(s):  
Flow Field ◽  
Characteristic Curve ◽  
Cross Flow ◽  
Flow Fields ◽  
Low Flow ◽  
Axial Fan ◽  
Ambient Flow ◽  
Fan Performance ◽  
Air Cooled Condensers ◽  
Axial Fans

In their application to air-cooled condensers, axial fans are often subject to the detrimental influence of ambient flow fields at their inlet or outlet. While effects have been investigated mostly under perpendicular cross-flow conditions on fans operating as part of an array in their target design point, this study aims at examining the integral influence of uniform ambient flow fields on a single axial fan over a wide operating range. For this purpose, a wind tunnel fan test rig has been designed and assessed. Multiple angles between uniform ambient flow field and fan axis are examined in their integral influence on the characteristic curve of two distinct industrial axial fans with varying inlet modifications. Increasingly with the fan flow rate, perpendicular inlet cross-flow was found to always have a detrimental influence on fan performance. The straight bladed fan reacted less sensitively than the forward skewed fan, and the adverse cross-flow influence could be reduced with an inlet guard grille and with short conical shroud extensions. Cross-flow at the fan outlet showed potential static fan pressure increases at low flow rates.

Aeroacoustic Optimization of a Pressure-Side Strut Configuration for Subsonic Axial Fans Using Statistical-Empirical Modelling

2018 ◽  
Author(s):  
Igor Neifach ◽  
Gi-Don Na ◽  
Frank Kameier ◽  
Nils Springer ◽  
Marco Wichers
Keyword(s):  
Residential Buildings ◽  
Statistical Design ◽  
Axial Fan ◽  
Noise Emission ◽  
Public Places ◽  
Empirical Modelling ◽  
Passive Construction ◽  
Cooling Fan ◽  
Rotor Stator Interaction ◽  
Axial Fans

This paper deals with the reduction of aerodynamically generated noise in passenger car Cooling-Fan-Modules (CFM), caused by the interaction between the impeller and the downstream-located strut configuration of the axial fan. Even after the car engine is switched off, the fan remains active, as long as cooling is required for certain vehicle components. Especially after a car has been parked in closed parking areas, in close proximity to residential buildings or public places, the noise emission can be a problem. This issue is addressed by dampening the rotor-stator-interaction through passive construction measures. In order to ensure optimal noise reduction, 8 critical design features of the struts are identified and investigated using statistical design of experiment methods (DoE). Based on the results, dedicated insights about the effects of concrete strut features on significant regions of the acoustic fan spectrum are obtained. Furthermore, an optimized strut configuration is derived and metrologically validated using a polyoptimization method. Compared to a current serial baseline configuration, a reduction of the overall sound pressure level by 2.6 dB(A), as well as a reduction of the blade passage frequency tone by 17.6 dB(A) is achieved.

Influence of blade skew on axial fan component noise

2017 ◽  
Vol 16 (4-5) ◽  
pp. 418-430 ◽  
Author(s):  
Gert Herold ◽  
Florian Zenger ◽  
Ennes Sarradj
Keyword(s):  
Test Chamber ◽  
Microphone Arrays ◽  
Blade Design ◽  
Axial Fan ◽  
Sound Sources ◽  
Acoustic Characteristics ◽  
Radiated Noise ◽  
Trailing Edges ◽  
Axial Fans ◽  
Operating Points

Microphone arrays can be used to detect sound sources on rotating machinery. For this study, experiments with three different axial fans, featuring backward-skewed, unskewed, and forward-skewed blades, were conducted in a standardized fan test chamber. The measured data are processed using the virtual rotating array method. Subsequent application of beamforming and deconvolution in the frequency domain allows the localization and quantification of separate sources, as appear at different regions on the blades. Evaluating broadband spectra of the leading and trailing edges of the blades, phenomena governing the acoustic characteristics of the fans at different operating points are identified. This enables a detailed discussion of the influence of the blade design on the radiated noise.

The Aerodynamic Interaction of Tip Leakage and Mainstream Flows in a Fully-Ducted Axial Fan

2004 ◽  
Author(s):  
Alessandro Corsini ◽  
Franco Rispoli ◽  
Geoff Sheard ◽  
Iain Kinghorn
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Vortical Flow ◽  
Aerodynamic Noise ◽  
Axial Fan ◽  
Noise Emission ◽  
Flow Mechanisms ◽  
Flow Effects

The three dimensional structures of the blade tip vortical flow field is herein discussed for an axial fan in a fully-ducted configuration. The investigation has been carried-out using an accurate in-house developed multi-level parallel finite element RANS solver, with the adoption of a non-isotropic two-equation turbulence closure. Due to the fully-ducted configuration the fan has a complex vortical flow field near the rotor tip. The tip clearance flows have been detected for operating conditions near peak efficiency and near stall, with multiple vortex formations being identified in both cases. The nature of the flow mechanisms in the fan tip region is correlated to the specific blade design features that promote reduced aerodynamic noise. It was found that the blade lean at the higher radii attenuates the sensitivity to leakage flow effects. Consequently, the rotor operates efficiently and with nearly unchanged noise emission approaching its throttling limit. The rotor loss behaviour, within the passage and downstream of it, is also discussed at both near design and part-load conditions.

Development of an Ultra-Quiet Fan for Computer Cooling Applications

2014 ◽  
Author(s):  
Zhenyu Wang ◽  
Hui Hu
Keyword(s):  
Flow Field ◽  
Noise Reduction ◽  
Sound Pressure ◽  
Field Measurements ◽  
Vortex Structures ◽  
Tip Clearance ◽  
Axial Fan ◽  
Fan Noise ◽  
Piv Measurements ◽  
Cooling Fan

We report the progress made in our recent study to develop an ultra-quiet axial fan for computer cooling applications. By using a commercially-available cooling fan as the baseline, a number of acoustically tailored modifications are implemented in order to reduce the noise level of the cooling fan, which includes optimizing the rotator blades and guide vanes according to axial fan design theory, adding an intake cone in the front of the hub to guide the airflow into the axial fan smoothly, and reducing the tip clearance to lower the noise generation due to tip vortex structures. A comparison study is conducted to measure the sound pressure level (SPL) of the reformed axial fan in an anechoic chamber, in comparison to that of the prototype fan, in order to assess the effects of the modifications on the fan noise reduction. The measurement results of our preliminary study reveal that, at the same flow rate, the SPL of the reformed fan would be up to 5 dB lower than that of the prototype fan. In addition to measuring the sound pressure levels (SPLs) of the fans, a digital particle image velocimetry (PIV) system is also used to conduct detailed flow field measurements to reveal the changes of the flow characteristics and unsteady vortex structures associated with the modifications. Besides conducting “free-run” PIV measurements to determine the ensemble-averaged statistics of the flow quantities such as mean velocity, Reynolds stress, and turbulence kinetic energy (TKE) distributions at the exit of the axial fan, “phase-locked” PIV measurements are also performed to elucidate further details about evolution of the unsteady vortex structures in fan exhaust in relation to the position of the rotating fan blades. The detailed flow field measurements are correlated with the SPL measurements in order to elucidate underlying physics associated with the fan noise reduction.

scholarly journals Low-pressure reversible axial fan designed with different specific work of elementary stages

2012 ◽  
Vol 16 (suppl. 2) ◽  
pp. 605-615 ◽  
Author(s):  
Bozidar Bogdanovic ◽  
Zivan Spasic ◽  
Jasmina Bogdanovic-Jovanovic
Keyword(s):  
Suction Side ◽  
Low Pressure ◽  
Standard Test ◽  
Specific Work ◽  
Spatial Curvature ◽  
Operating Characteristics ◽  
Test Rig ◽  
Axial Fan ◽  
Air Intake ◽  
Axial Fans

Low-pressure axial fan impellers designed according to the principle of equal specific work of all elementary stages have blades whose profile near the fan hub is under a significantly larger inclination angle than at the impeller periphery. In order to minimize the spatial curvature of the fan blades and the fan hub length, impeller blades of low-pressure axial fans can be designed with different specific work of elementary stages, so that the specific work of elementary stages is smaller at the hub than at the periphery. This paper presents the operating characteristics of a low-pressure reversible axial fan with straight blade profiles, designed with different specific work of elementary stages. The fan was tested on a standard test rig, with air intake loading on the suction side of the fan.

scholarly journals Experiment-Based Preliminary Design Guidelines for Consideration of Profile Vortex Shedding From Low-Speed Axial Fan Blades

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Gábor Daku ◽  
János Vad
Keyword(s):  
Vortex Shedding ◽  
Design Guidelines ◽  
Preliminary Design ◽  
Axial Fan ◽  
Noise Emission ◽  
Blade Vibration ◽  
Low Speed ◽  
Blunt Trailing Edge ◽  
Axial Fans ◽  
Semi Empirical

Abstract This paper presents hot-wire measurements in a wind tunnel, close downstream of basic models of blade sections being representative for low-speed, low-Reynolds number axial fans, in order to explore the signatures of vortex shedding (VS) from the blade profiles. Using the Rankine-type vortex approach, an analytical model was developed on the velocity fluctuation represented by the vortex streets, as an aid in evaluating the experimental data. The signatures of profile VS were distinguished from blunt trailing-edge VS based on Strouhal numbers obtained from the measurements in a case-specific manner. Utilizing the experimental results, the semi-empirical model available in the literature for predicting the frequency of profile VS was extended to low-speed axial fan applications. On this basis, quantitative guidelines were developed for the consideration of profile VS in preliminary design of axial fans in the moderation of VS-induced blade vibration and noise emission.

scholarly journals Axial fan blade vibration under inlet cross-flow

2017 ◽  
Author(s):  
Till Heinemann ◽  
Stefan Becker
Keyword(s):  
Flow Rate ◽  
Power Plants ◽  
Thermal Power ◽  
Amplitude Spectrum ◽  
Cross Flow ◽  
Flow Conditions ◽  
Axial Fan ◽  
Blade Vibration ◽  
Fan Blade ◽  
Operating Points

In thermal power plants equipped with air-cooled condensers, axial cooling fans operate under the influence of ambient flow fields. Under inlet cross-flow conditions, the resultant asymmetric flow field is known to introduce additional harmonic forces to the fan blades. This effect has previously been studied only numerically or using blade mounted strain gauges. For this study, Laser Scanning Vibrometry was used to assess fan blade vibration under inlet cross-flow conditions in an adapted fan test rig inside a wind tunnel test section. Two co-rotating laser beams scanned a low pressure axial fan, resulting in spectral, phase resolved surface vibration patterns of the fan blades. Two distinct operating points were examined, with and without inlet cross-flow influence. While almost identical fan vibration patterns were found for both reference operating points, overall blade vibration increased by 100% at low fan flow rate due to cross-flow, and by 20% at high fan flow rate. While numerically predicted natural frequency modes could be confirmed from experimental data as minor peaks in the vibration amplitude spectrum, they were not excited significantly by cross-flow. Instead, primarily higher rotation rate harmonics were amplified, i.a. a synchronous blade tip flapping was strongly excited at the blade pass frequency.

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