Noise Prediction in Design of Low Pressure Rotor-Only Axial Fans

2011 ◽  
Author(s):  
Jie Zhang ◽  
Shaoping Zhou ◽  
Xiaoling Ge
Keyword(s):  
Sound Pressure ◽  
Broad Band ◽  
Low Pressure ◽  
Noise Prediction ◽  
Blade Design ◽  
Prediction Program ◽  
Aeroacoustic Noise ◽  
Blunt Trailing Edge ◽  
Axial Fans ◽  
Semi Empirical

A noise prediction program has been incorporated into a blade design process of the arbitrary vortex flow rotor-only axial fans which are widely used in low pressure applications. Parametrical studies of different geometrical designs are conducted to investigate the influence on noise radiation from axial fans. The noise prediction program is based on the Carolus’s semi-empirical model, in which the broad-band aeroacoustic noise is mostly attributed to three independent sources: incident turbulence, turbulent boundary layer, and blunt trailing edge. In addition, the well-known Fukano’s vortex shedding model is also utilized for indicative comparison. It is indicated that the total sound pressure level is most sensitive to the flow relative velocity, while the chord length can be considered as a secondary cause.

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

2020 ◽  
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 The 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 consideration of profile VS in preliminary design of axial fans in moderation of VS-induced blade vibration and noise emission.

Acceptable Levels of Tonal and Broad-Band Repetitive and Continuous Sounds during the Performance of Nonauditory Tasks

1995 ◽  
Vol 81 (3) ◽  
pp. 803-816 ◽  
Author(s):  
Ulf Landström ◽  
Anders Kjellberg ◽  
Marianne Byström
Keyword(s):  
Reaction Time ◽  
Sound Pressure ◽  
Broad Band ◽  
Reaction Time Task ◽  
Simple Reaction Time Task ◽  
Reasoning Test ◽  
Band Noise ◽  
Time Test ◽  
The Difference ◽  
Reaction Time Test

Three groups of 24 subjects were exposed to a 1000–Hz tone or broad band noise in a sound chamber. During the exposures subjects were engaged in an easy reaction time test or a difficult grammatical reasoning test. For each exposure and work subjects adjusted the noise to a tolerance level defined by its interference with task performance. During the simple reaction-time task significantly higher sound-pressure levels were accepted than during the reasoning test. At the tonal exposure, much lower levels were accepted than during the exposure to broad-band noise. For continuous sound exposures much higher levels were accepted than for noncontinuous exposures. For tonal exposures the difference was approximately 5 dB, for the broad-band exposures approximately 9 dB. In a separate study the effects of the noncontinuity of the noise and pauses were analysed. The raised annoying effect of the noncontinuous noise was not more affected by the noncontinuity of the noise periods than by the noncontinuity of the pauses. The results imply that the annoying reactions to the sound will be increased for repetitive noise and that the reaction is highly influenced by the over-all noncontinuity of the exposure.

scholarly journals Low Pressure Gas Electron Diffraction: an Experimental Setup and Case Studies

2020 ◽  
Author(s):  
Yury Vishnevskiy ◽  
Sebastian Blomeyer ◽  
Christian G. Reuter
Keyword(s):  
Electron Diffraction ◽  
Benzoic Acid ◽  
Low Pressure ◽  
Molecular Structures ◽  
Gas Electron Diffraction ◽  
Experimental Setup ◽  
Critical Comparison ◽  
Diffraction Patterns ◽  
Predicted Values ◽  
Semi Empirical

<div>Principles of low pressure gas electron diffraction(LPGED) are introduced. An experimental setup has</div><div>been constructed for measuring electron diffraction patterns of gaseous samples at pressures below 10−3</div><div>mbar. Test measurements have been performed for benzoic acid at T = 287 K corresponding to a vapor </div><div>pressure of the substance P = 2 × 10−4 mbar, for iodoform CHI3 at T = 288 K (P = 4 × 10−4 mbar) and for carbon tetraiodide CI4 at T = 290K (P = 1 × 10−4 mbar). Due to the low experimental temperature thermal decomposition of CI4 has been prevented, which was unavoidable in previous classical measurements at higher temperatures.</div><div>From the obtained data the molecular structures have been successfully refined. The most important</div><div>semi-empirical equilibrium molecular parameters are re(Car–Car)av = 1.387(5) Å in benzoic acid, re(C–I)</div><div>= 2.123(3) Å in iodoform and re(C–I) = 2.133(7) Å in carbon tetraiodide. The determined parameters</div><div>showed consistency with theoretically predicted values. A critical comparison with results of the earlier</div><div>investigations has also been done.</div>

Effect of Pantograph and Bogie on Interior Noise of High-Speed Train in Tunnel

2013 ◽  
Vol 664 ◽  
pp. 191-196
Author(s):  
You Gang Xiao ◽  
Yu Shi
Keyword(s):  
High Speed ◽  
Sound Pressure ◽  
Broad Band ◽  
Pressure Level ◽  
Channel Noise ◽  
High Speed Train ◽  
Noise Sources ◽  
Vehicle Noise ◽  
Measurement And Analysis ◽  
Analysis System

For clarifying the noise in tunnel affected by pantograph and bogie, which are the most important noise sources, the noises near pantograph and bogie in a high-speed train were tested by multi-channel noise measurement and analysis system in tunnel, and compared with those measured outside the High-speed train and on an open field. The results show that the interior vehicle noise is spatially non-homogeneous in the whole carriage, the larger sound pressure level (SPL) near pantograph are next to ceiling, and near bogie next to floor. The noise spectra show a broad band feature, and dominated by the frequency contents among 100Hz-2kHz, so the countermeasures against noise should be within these range.

Hearing Loss in Relation to Physical Properties of Middle Ear Effusions

1980 ◽  
Vol 89 (3_suppl) ◽  
pp. 185-189 ◽  
Author(s):  
M. L. Wiederhold ◽  
J. G. Vap ◽  
J. T. Zajtchuk ◽  
R. E. Paggi
Keyword(s):  
Hearing Loss ◽  
Physical Properties ◽  
Middle Ear ◽  
Sound Pressure ◽  
Broad Band ◽  
Type B ◽  
Control Series ◽  
Middle Ear Pressure ◽  
Flat Type ◽  
Significant Difference

Hearing loss was measured in cats after ligation of the eustachian tube (ET) on one side to produce middle ear effusions. Auditory nerve responses to broad-band clicks were recorded from the ear canal. Plots of N1 response amplitude and latency versus click sound pressure level (SPL) were constructed. Hearing loss was determined as the average displacement along the SPL axis of the latency plot, relative to a previously recorded control series. Viscosity of effusion was measured with a cone and plate viscometer. Specific gravity was measured using a 1 cc pycnometer. Middle ear pressure was assessed tympanographically. After ET ligation, all cats developed negative middle ear pressure within three days and flat (type B) tympanograms within seven days. Hearing loss also developed early and became maximal at about three weeks. Tympanocentesis yielded either thin fluid or glue-like effusions in nearly equal numbers. The data indicate there is not a significant difference between the amount of hearing loss associated with thin fluids or with glue. Viscosity is not clearly related to the duration of time the fluid is present in the middle ear. There is a significant positive correlation between the amount of hearing loss and the volume of fluid present in the middle ear. Thus, the amount of hearing loss appears to depend only on the volume of effusion and is not significantly dependent on other physical properties of the fluid.

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