Experimental Analysis of Simultaneous Non-Harmonically Related Unstable Modes in a Swirled Combustor

2011 ◽  
Author(s):  
Ammar Lamraoui ◽  
Franck Richecoeur ◽  
Se´bastien Ducruix ◽  
Thierry Schuller
Keyword(s):  
High Speed ◽  
Sound Pressure ◽  
Acoustic Pressure ◽  
Source Term ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Combustion Instabilities ◽  
Acoustic Response ◽  
Flame Region ◽  
Two Peaks

The present study investigates combustion instabilities generated in a turbulent swirled combustor featuring two non-harmonically related unstable modes. Sound pressure and chemiluminescence spectra show the presence of two peaks located around 180 Hz and 280 Hz during unstable operation. The low frequency acoustic response of the test-rig is then analyzed using a two-coupled-cavity model including a realistic impedance of the system at the premixer inlet. This analytical approach is used to link the two observed frequencies to the first chamber and premixer modes respectively. Analytical predictions are compared with acoustic pressure measurements to determine the structure of these modes. The Rayleigh source term in the energy balance is also computed and shows that the two modes feed acoustic energy simultaneously in the system. High-speed PIV data gathered under unstable operation are filtered around these two frequencies to obtain phase conditioned images. Results show that the unsteady flow in the flame region features distinct dynamics associated to a bulk longitudinal oscillation of the flow in the flame arms at 180 Hz and large wrinkles in the radial direction at 280 Hz.

scholarly journals Acoustic metastructure for effective low-frequency acoustic energy harvesting

2018 ◽  
Vol 37 (4) ◽  
pp. 1015-1029 ◽  
Author(s):  
Ming Yuan ◽  
Ziping Cao ◽  
Jun Luo ◽  
Roger Ohayon
Keyword(s):  
Energy Harvesting ◽  
Sound Pressure ◽  
Electrical Power ◽  
Low Frequency ◽  
Electrical Energy ◽  
Acoustic Energy ◽  
Resonant Phenomenon ◽  
Acoustic Energy Harvesting ◽  
Isolation Performance ◽  
Rubber Film

In this study, a multifunctional acoustic metastructure is proposed to achieve both effective low-frequency sound isolation and acoustic energy harvesting. A metallic substrate with proof mass is adopted to generate the local resonant phenomenon for the purpose of overcoming the drawbacks of the previous rubber film-based acoustic metastructure; the latter usually requires an elaborate tension process. Numerical simulations show that the proposed structure exhibits excellent noise isolation performance in the low-frequency band. Meanwhile, the incident sound energy can be converted into electrical energy with the help of an added piezoelectric patch. Numerical simulation results indicate that the harvested energy can reach the mW level. The parameters’ influence on the metastructure’s vibro-acoustic and energy harvesting performance are discussed in detail. An optimized configuration is selected and used for experimental study. It is demonstrated that 0.21 mW electrical power at 155 Hz can be harvested by the proposed metastructure under 114 dB sound pressure excitation.

scholarly journals A Piezoelectric-Driven Rock-Drilling Device for Extraterrestrial Subsurface Exploration

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
He Li ◽  
Yi Shen ◽  
Qingchuan Wang ◽  
Yinchao Wang ◽  
Deen Bai ◽  
...  
Keyword(s):  
High Speed ◽  
Electric Energy ◽  
Low Frequency ◽  
Reference Method ◽  
Acoustic Energy ◽  
Biological Information ◽  
Sample Collection ◽  
Percussive Drilling ◽  
Rock Drilling ◽  
Gravitational Fields

The rocks on extraterrestrial objects contain plenty of original geological and biological information. Drilling and sampling are an essential task in lunar exploration or future explorations of other planets like mars. Due to the limitation of payloads, energies, and drill pressure, the investigation of a lightweight and low-powered rock-drilling device is crucial for explorations of distant celestial bodies. The ultrasonic drill driven by piezoelectric ceramics is a new drilling device that can adapt to the arduous space rock-drilling tasks in weak gravitational fields. An ultrasonic drill suitable for mounting on a planetary rover’s robotic arm is developed. The ultrasonic transducer’s energy conversion from electric energy to acoustic energy and the energy transmission from the horn’s high-frequency vibration to the drill stem’s low-frequency impact motion are analyzed to guide the design of the drill. To deeply understand the percussive drilling mechanism under high-speed impact, the interaction between the drill stem and the rock is simulated using LS-DYNA software. Drilling experiments on rocks with different hardness grades are conducted. The experiment results illustrate that the ultrasonic drill can penetrate into the hard rocks only taking a force of 6 N and a power consumption of 15 W. The study of ultrasonic drill will provide a reference method for sample collection of extraterrestrial rocks.

Analysis of the Influence of Racks on High Speed Train Interior Noise Using Finite Element Method

2014 ◽  
Vol 675-677 ◽  
pp. 257-260 ◽  
Author(s):  
Di Wu ◽  
Jian Min Ge
Keyword(s):  
Finite Element ◽  
Sound Pressure Level ◽  
High Speed ◽  
Sound Pressure ◽  
Low Frequency ◽  
Sound Field ◽  
Pressure Level ◽  
High Speed Train ◽  
Fe Method ◽  
Proposed Model

In this paper, the finite element (FE) method was used for simulation of the low-frequency sound field in high speed train compartments. The proposed model was validated using experimental results. The FE models of the train compartments with and without racks were established respectively, and the sound pressure level of the standard point and sound field distribution in these two cases were compared. The results showed that the A-weighted sound pressure level of the standard point was 1.2 dB lower when there is no rack in the compartment.

scholarly journals Piezoelectric nanofiber/polymer composite membrane for noise harvesting and active acoustic wave detection

2019 ◽  
Vol 1 (12) ◽  
pp. 4909-4914
Author(s):  
Nuanyang Cui ◽  
Xiaofeng Jia ◽  
Anan Lin ◽  
Jinmei Liu ◽  
Suo Bai ◽  
...  
Keyword(s):  
Acoustic Wave ◽  
Polymer Composite ◽  
Composite Membrane ◽  
Sound Pressure ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Wave Detection

The PENG exhibited a good performance for harvesting and detecting low-frequency acoustic energy with a minimum sound pressure of 0.18 Pa.

Observation of Particle Flocculation by kHz-Band Ultrasonic Waves in Solid-Liquid Mixture (Effects of Frequency and Sound Pressure)

2015 ◽  
Author(s):  
Yasuhiro Sugimoto ◽  
Tatsuya Haruna ◽  
Keiichi Sato
Keyword(s):  
Ultrasonic Wave ◽  
High Speed ◽  
Sound Pressure ◽  
Liquid Mixture ◽  
Present Report ◽  
Low Frequency ◽  
Video Camera ◽  
Ultrasonic Waves ◽  
Water Jet Cutting ◽  
Solid Liquid

It is important to separate and collect particles from solid-liquid mixture in order to reduce in environmental load and treatment cost of waste fluid. In this study, we try to separate and collect particles from the mixture by ultrasonic waves with relatively low frequency. In the present report, we use slurry of alumina abrasive as removal particles that use for polish and water jet cutting, etc. The particles are fully stirred in test water and then ultrasonic waves are irradiated with some frequencies. The particles behavior observed by a high-speed video camera is analyzed by a time series image analysis and correlated with sound pressure distribution. Particles flocculate to some layers like white bands that correspond to node of sound pressure after irradiation of ultrasonic wave. It is found that particles begin to move just after ultrasonic wave irradiation and flocculate clearly with the increase in sound pressure.

scholarly journals Numerical simulation of the slipstream and aeroacoustic field around a high-speed train

2016 ◽  
Vol 231 (6) ◽  
pp. 740-756 ◽  
Author(s):  
Chunli Zhu ◽  
Hassan Hemida ◽  
Dominic Flynn ◽  
Chris Baker ◽  
Xifeng Liang ◽  
...  
Keyword(s):  
Sound Pressure Level ◽  
High Speed ◽  
Sound Pressure ◽  
Low Frequency ◽  
Pressure Level ◽  
Broadband Noise ◽  
Full Scale ◽  
High Speed Train ◽  
Noise Characteristics ◽  
Simulation Results

The flow field and sound propagation around a three-coach 1/8th scale high-speed passenger train were obtained using a detached-eddy simulation and the Ffowcs-Williams and Hawkings acoustic analogy. The Reynolds number of flow based on the train height and speed was 2,000,000. The numerical results of the flow and aeroacoustic fields were validated using wind tunnel experiments and full-scale data, respectively. Features of overall sound pressure level, sound pressure level and A-weighted sound pressure level of typical measuring points are discussed. The sound propagated by a high-speed train is shown as a broadband noise spectrum including tonal component, where high sound pressure levels are concentrated on the low-frequency range from 10 Hz to 300 Hz. The inter-carriage gap is found to cause distinct tonal noise in contrast to the other parts of the train that cause a broadband noise. The negative log law has been used to study the influence of distance from the centre of track on the sound pressure level, where a good fit is shown at low-frequency ranges. The peak values of A-weighted sound pressure level from both full-scale experiment and simulation results occur at approximately 1 kHz, where simulation results show almost the same range as the experiment. The surface of each component of the train as well as the whole train are chosen as the integral surface for the Ffowcs-Williams and Hawkings computation of the far-field noise characteristics. It was found that the sound source generated by a high-speed train is mainly dipole, and the largest noise was obtained from the leading bogie. The results of this paper provide, for the first time, a better understanding of the aeroacoustic field around a three-coach train model, and the paper has the potential to assist engineers to design high-speed trains with aeroacoustic noise reduction in a better manner.

scholarly journals The flow and acoustic characteristics of underwater gas jets from large vertical exhaust nozzles

2018 ◽  
Vol 37 (1) ◽  
pp. 74-89
Author(s):  
Tiancheng Miao ◽  
Jingting Liu ◽  
Shijie Qin ◽  
Ning Chu ◽  
Dazhuan Wu ◽  
...  
Keyword(s):  
High Speed ◽  
Gas Flow ◽  
Sound Pressure ◽  
Low Frequency ◽  
Video Camera ◽  
Bubble Behavior ◽  
Acoustic Characteristics ◽  
Gas Jets ◽  
Audio Tape Recorder ◽  
Frequency Behavior

The flow and acoustic characteristics of underwater gas jets exhausted from large vertical nozzles are experimentally investigated in this work with gas flow rates of 30–150 m3/h, nozzle widths of d = 10 mm, 20 mm, 30 mm, and 40 mm. A high-speed digital video camera is used to examine bubble behavior and flow regimes. Sound pressure is measured by two hydrophones and recorded by a digital audio tape recorder. The audio and video signals are synchronized to find out the relationship between sound and gas behavior. Experimental results indicate that the general behavior of gas exhausted into water is of periodical necking and expansion. Sound pressure peaks are mostly excited by necking in two ways: pinch-off and redial expansion. Necking itself is a kind of low frequency behavior, corresponding to strong low frequency sounds. Moreover, necking can force the growing bubble to oscillate and emit broadband sound. As the gas velocity increases, necking would happen more frequently, and gas jets would grow into larger volume in shorter time, and then the sound radiated from the gas jets would have higher frequency and larger amplitude.

scholarly journals The Flow Noise Characteristics of a Control Valve

2014 ◽  
Vol 8 (1) ◽  
pp. 960-966
Author(s):  
Xin Nie ◽  
Yangyang Zhu ◽  
Lei Li
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Acoustic Pressure ◽  
Low Frequency ◽  
Control Valve ◽  
Pressure Amplitude ◽  
Acoustic Analogy ◽  
Flow Noise ◽  
Noise Characteristics ◽  
Valve Opening

Using the enterprise’s valve as the research object, the research studied the characteristics of the flow field and noise of the valve. The theory of (LES) LES and Lighthill acoustic analogy is applied to study the flow noise at 100% opening and at 70% opening of valve in the same flow. The result shows that the region of variation of pressure and velocity is in the valve sleeve window. The sound pressure spectrum characteristics of the same group of monitoring points were similar, when they were in low frequency. Acoustic pressure amplitude was observed to be relatively small, when monitoring points were in high frequency. When the valve opening decreased, because of the throttle effect of valve windows, the whole dB SPL of valve became strong. The noise outside the valve exhibited dipole characteristics.

Real Ear Sound Pressure Levels Developed by Three Portable Stereo System Earphones

1992 ◽  
Vol 1 (4) ◽  
pp. 52-55 ◽  
Author(s):  
Gail L. MacLean ◽  
Andrew Stuart ◽  
Robert Stenstrom
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Low Frequency ◽  
Test System ◽  
Output Frequency ◽  
Frequency Effects ◽  
Adult Men ◽  
Frequency Responses ◽  
Significant Difference ◽  
Sound Pressure Levels

Differences in real ear sound pressure levels (SPLs) with three portable stereo system (PSS) earphones (supraaural [Sony Model MDR-44], semiaural [Sony Model MDR-A15L], and insert [Sony Model MDR-E225]) were investigated. Twelve adult men served as subjects. Frequency response, high frequency average (HFA) output, peak output, peak output frequency, and overall RMS output for each PSS earphone were obtained with a probe tube microphone system (Fonix 6500 Hearing Aid Test System). Results indicated a significant difference in mean RMS outputs with nonsignificant differences in mean HFA outputs, peak outputs, and peak output frequencies among PSS earphones. Differences in mean overall RMS outputs were attributed to differences in low-frequency effects that were observed among the frequency responses of the three PSS earphones. It is suggested that one cannot assume equivalent real ear SPLs, with equivalent inputs, among different styles of PSS earphones.

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