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1
Zhang, Lei, Shoufang Liang, and Chenxing Hu. "Flow and Noise Characteristics of Centrifugal Fan under Different Stall Conditions." Mathematical Problems in Engineering 2014 (2014): 1–9. http://dx.doi.org/10.1155/2014/403541.
Повний текст джерелаАнотація:
An implicit, time-accurate 3D Reynolds-averaged Navier-Stokes (RANS) solver is used to simulate the rotating stall phenomenon in a centrifugal fan. The goal of the present work is to shed light on the flow field and particularly the aerodynamic noise at different stall conditions. Aerodynamic characteristics, frequency domain characteristics, and the contours of sound power level under two different stall conditions are discussed in this paper. The results show that, with the decrease of valve opening, the amplitude of full pressure and flow fluctuations tends to be larger and the stall frequency remains the same. The flow field analysis indicates that the area occupied by stall cells expands with the decrease of flow rate. The noise calculation based on the simulation underlines the role of vortex noise after the occurrence of rotating stall, showing that the high noise area rotates along with the stall cell in the circumferential direction.
2
Čudina, M. "Noise generation in vane axial fans due to rotating stall and surge." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 215, no. 1 (January 1, 2001): 57–64. http://dx.doi.org/10.1243/0954406011520517.
Повний текст джерелаАнотація:
A characteristic of axial flow fans is instabilities in their performance and noise in partial load operation. These instabilities are a consequence of rotating stall created in the rotor blade and/or in the guide vane cascade. At some operating conditions the rotating stall caused the appearance of a surge representing the lowest region of fan operating stability. The rotating stall and especially surge caused a steep increase in the emitted noise and lowered the performance of the fan. The present paper highlights the rotating stall generation phenomenon and its influence on the emitted total noise level and noise spectra for axial flow fans with inlet and outlet guide vanes.
3
Lacagnina, Giovanni, Paruchuri Chaitanya, Jung-Hoon Kim, Tim Berk, Phillip Joseph, Kwing-So Choi, Bharathram Ganapathisubramani, et al. "Leading edge serrations for the reduction of aerofoil self-noise at low angle of attack, pre-stall and post-stall conditions." International Journal of Aeroacoustics 20, no. 1-2 (February 1, 2021): 130–56. http://dx.doi.org/10.1177/1475472x20978379.
Повний текст джерелаАнотація:
This paper addresses the usefulness of leading edge serrations for reducing aerofoil self-noise over a wide range of angles of attack. Different serration geometries are studied over a range of Reynolds number [Formula: see text]. Design guidelines are proposed that permit noise reductions over most angles of attack. It is shown that serration geometries reduces the noise but adversely effect the aerodynamic performance suggesting that a trade-off should be sought between these two considerations. The self-noise performance of leading edge serrations has been shown to fall into three angle of attack (AoA) regimes: low angles where the flow is mostly attached, moderate angles where the flow is partially to fully separated, and high angles of attack where the flow is fully separated. Leading edge serrations have been demonstrated to be effective in reducing noise at low and high angles of attack but ineffective at moderate angles. The noise reduction mechanisms are explored in each of three angle regimes.
4
Laratro, Alex, Maziar Arjomandi, Benjamin Cazzolato, and Richard Kelso. "Self-noise of NACA 0012 and NACA 0021 aerofoils at the onset of stall." International Journal of Aeroacoustics 16, no. 3 (April 2017): 181–95. http://dx.doi.org/10.1177/1475472x17709929.
Повний текст джерелаАнотація:
The aerodynamic noise of a NACA 0012 and NACA 0021 aerofoil is measured and compared in order to determine whether there are differences in their noise signatures with a focus on the onset of stall. Measurements of the self-noise of each aerofoil are measured in an open-jet Anechoic Wind Tunnel at Reynolds numbers of 64,000 and 96,000, at geometric angles of attack from −5° through 40° at a resolution of 1°. Further measurements are taken at Re = 96,000 at geometric angles of attack from −5 through 16° at a resolution of 0.5°. Results show that while the noise generated far into the stall regime is quite similar for both aerofoils the change in noise level at the onset of stall is significantly different between the two aerofoils with the NACA 0021 exhibiting a much sharper increase in noise levels below a chord-based Strouhal number of Stc = 1.1. This behaviour is consistent with the changes in lift of these aerofoils as well as the rate of collapse of the suction peak of a NACA 0012 aerofoil under these flow conditions.
5
Xiao-Hong Qiu, Xiao-Hong Qiu, Jia-Li Chen Xiao-Hong Qiu, and Zi-Ying Ao Jia-Li Chen. "Stall Warning Algorithm of Axial Compressor Based on SSA-DBN." 電腦學刊 33, no. 3 (June 2022): 059–71. http://dx.doi.org/10.53106/199115992022063303005.
Повний текст джерелаАнотація:
<p>To solve the problem of stall warning for axial compressors, this paper proposes a stall warning algorithm based on the sparrow search algorithm, which optimizes the deep belief network. The deep belief network is trained by using deep learning to extract the FFT spectrum of compressor stall experiment data directly as the feature vector. To improve the accuracy of DBN classification, parameters of hidden layer nodes n and initial weights w of DBN were optimized by SSA algorithm, and stall warning algorithm model of SSA-DBN axial-flow compressor was established. The experimental results of the algorithms show that the stall data at each speed is at least 0.1～0.3s in advance for early warning. This method is 0.075~0.281s ahead of the various models from the past to the present, and noise is superimposed on the experimental data to verify the Robustness of the way, better surge warning margin performance, and engineering practicability. </p> <p> </p>
6
Bianchi, Stefano, Alessandro Corsini, and Anthony G. Sheard. "Experiments on the Use of Signal Visualization Technique for In-Service Stall Detection in Industrial Fans." Advances in Acoustics and Vibration 2013 (May 7, 2013): 1–10. http://dx.doi.org/10.1155/2013/610407.
Повний текст джерелаАнотація:
The paper describes a stalldetection criterion based on the use of symmetrised dot pattern (SDP) visual waveform analysis and the stallwarning methodology based on a recently developed analysis. The experimental study explores the capability of the SDP technique to detect the stall incipience and evolution in the presence of low signal-to-noise ratios, that is, a noisy working environment. Moreover, the investigation presents a systematic analysis on the probe position’s influence with respect to the fan section. As such, the SDP technique in combination with an acoustic measurement is able to create a visual pattern that one can use to detect stall from potentially any location around the fan/duct system.
7
Cudina, Mirko. "Noise generation by rotating stall and surge in vane-axial fans." Noise Control Engineering Journal 48, no. 3 (2000): 77. http://dx.doi.org/10.3397/1.2827969.
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8
Chun, Guo, Wang Mingnian, and Tang Zhaozhi. "A Study on Surge and Stall under the Interaction of Parallel Axial flow fan in Tunnel." Noise & Vibration Worldwide 42, no. 11 (December 2011): 9–14. http://dx.doi.org/10.1260/0957-4565.42.11.9.
Повний текст джерелаАнотація:
In the ventilation design for tunnels above 10km, an axial flow fan of great power needs to be set in ventilation shafts. There are few provisions on the setting modes and less discussion of parallel axial flow fan mode in the Specifications for Design of Ventilation and Lighting of Highway Tunnels. All of these bring a lot of difficulties about the axial fan selection, layout and control design. There is no specialized research on axial flow fan for tunnels and no studies on surge and stall under the interaction of parallel axial flow fan in tunnel in spite of the more and more application of parallel axial flow fan. So, this paper conducts a study on surge and stall under the interaction of parallel axial flow fan in tunnels. Through the study on the operating principle and analysis of parallel axial flow fan, we can know that the noise will increase suddenly, which will in turn result in fan vibration and running instability once the stall occurs. When a fan surges, the air volume and pressure, the motor current will fluctuate sharply, which brings significantly increased vibration and noise. At the same time, the rotary blade and the shell are subject to considerable stress effects and the fan will possibly suffer from great damage. The surge will occur in the unstable zone of axial fan performance curve. The strong pulsation and periodic oscillation of the air flow will increase the noise, which is a serious damage to the fan. So an axial fan should avoid this zone in running. With two axial flow fans of the same power parallel, the mutual influence is not very great. Therefore this research will focus on the efficiency in the case of two fans with a high and a low power parallel. Stall will occur if the outside pressure is greater than the outlet pressure. Once the stall happens, the noise will increase suddenly, which will in turn result in fan vibration and running instability. When two fans parallel, i.e. when the power ratio of the parallel fans is over 5.3, the possibility of the small fan's stall is high, otherwise it is small. With regard to the running efficiency of parallel axial flow fans and the starting safety, it is better to parallel two fans, and the fans with adjustable movable vanes or frequency control or the ordinary nonadjustable fans can be used.
9
Okada, Ken. "Experiences with Flow-Induced Vibration and Low Frequency Noise Due to Rotating Stall of Centrifugal Fan." Journal of Low Frequency Noise, Vibration and Active Control 6, no. 2 (June 1987): 76–87. http://dx.doi.org/10.1177/026309238700600204.
Повний текст джерелаАнотація:
In recently constructed electric power plants, the forced draft fan (FDF), induced draft fan (IDF) and boost up fan (BUF) centrifugal fans and duct-systems have become larger in capacity and limited in space every year. As a centrifugal fan is enlarged, the diameter of the impeller is enlarged and its rotating speed is lowered. Therefore, there is an increasing tendency to generate a low frequency noise.5 In the case of an IDF or BUF, the rotating stall of the centrifugal fan frequently causes low frequency noise, since the inlet flow is often throttled during operation. If the hydrodynamic and acoustical characteristics are insufficient, a strong flow-induced vibration with low frequency noise is generated in the fan-duct system, and not only are problems caused in terms of structural strength, but also physical and physiological problems are induced due to low frequency noise.
10
Bertagnolio, Franck, Helge Aa Madsen, Andreas Fischer, and Christian Bak. "A semi-empirical airfoil stall noise model based on surface pressure measurements." Journal of Sound and Vibration 387 (January 2017): 127–62. http://dx.doi.org/10.1016/j.jsv.2016.09.033.
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11
Laratro, Alex, Maziar Arjomandi, Benjamin Cazzolato, and Richard Kelso. "Self-noise and directivity of simple airfoils during stall: An experimental comparison." Applied Acoustics 127 (December 2017): 133–46. http://dx.doi.org/10.1016/j.apacoust.2017.05.027.
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12
Tao, Ran, Xiaoran Zhao, and Zhengwei Wang. "Evaluating the Transient Energy Dissipation in a Centrifugal Impeller under Rotor-Stator Interaction." Entropy 21, no. 3 (March 11, 2019): 271. http://dx.doi.org/10.3390/e21030271.
Повний текст джерелаАнотація:
In fluid machineries, the flow energy dissipates by transforming into internal energy which performs as the temperature changes. The flow-induced noise is another form that flow energy turns into. These energy dissipations are related to the local flow regime but this is not quantitatively clear. In turbomachineries, the flow regime becomes pulsating and much more complex due to rotor-stator interaction. To quantitatively understand the energy dissipations during rotor-stator interaction, the centrifugal air pump with a vaned diffuser is studied based on total energy modeling, turbulence modeling and acoustic analogy method. The numerical method is verified based on experimental data and applied to further simulation and analysis. The diffuser blade leading-edge site is under the influence of impeller trailing-edge wake. The diffuser channel flow is found periodically fluctuating with separations from the blade convex side. Stall vortex is found on the diffuser blade trailing-edge near outlet. High energy loss coefficient sites are found in the undesirable flow regions above. Flow-induced noise is also high in these sites except in the stall vortex. Frequency analyses show that the impeller blade frequency dominates in the diffuser channel flow except in the outlet stall vortexes. These stall vortices keep their own stall frequency which is about 1/5 impeller frequency with high energy loss coefficient but low noise level. Results comparatively prove the energy dissipation mechanism in the centrifugal air pump under rotor-stator interaction. Results also provide the quantitative basis for turbomachinery’s loss reduction design.
13
Zhang, Lei, Rui Wang, and Songling Wang. "Simulation of Broadband Noise Sources of an Axial Fan under Rotating Stall Conditions." Advances in Mechanical Engineering 6 (January 2014): 507079. http://dx.doi.org/10.1155/2014/507079.
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14
Laratro, Alex, Maziar Arjomandi, Richard Kelso, and Benjamin Cazzolato. "A discussion of wind turbine interaction and stall contributions to wind farm noise." Journal of Wind Engineering and Industrial Aerodynamics 127 (April 2014): 1–10. http://dx.doi.org/10.1016/j.jweia.2014.01.007.
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15
Mascarenhas, David, Benjamin Cotté, and Olivier Doaré. "Synthesis of wind turbine trailing edge noise in free field." JASA Express Letters 2, no. 3 (March 2022): 033601. http://dx.doi.org/10.1121/10.0009658.
Повний текст джерелаАнотація:
The proposed sound synthesis tool converts a physics-based frequency-domain model of wind turbine trailing edge noise to a time-domain signal while accounting for the appropriate time shift due to the propagation between the moving blades and the fixed observer. A window function that implements cross-fading between consecutive signal grains is proposed and a method to objectively estimate the influence of the synthesis parameters is described. As the synthesis tool is independent of the aerodynamic noise model, it can be readily adapted to auralize other noise sources such as turbulent inflow noise or stall noise.
16
Butt, Abdul Hadi, Bilal Akbar, Jawad Aslam, Naveed Akram, Manzoore Elahi M. Soudagar, Fausto Pedro García Márquez, Md Yamin Younis, and Emad Uddin. "Development of a Linear Acoustic Array for Aero-Acoustic Quantification of Camber-Bladed Vertical Axis Wind Turbine." Sensors 20, no. 20 (October 21, 2020): 5954. http://dx.doi.org/10.3390/s20205954.
Повний текст джерелаАнотація:
Vertical axis wind turbines (VAWT) are a source of renewable energy and are used for both industrial and domestic purposes. The study of noise characteristics of a VAWT is an important performance parameter for the turbine. This study focuses on the development of a linear microphone array and measuring acoustic signals on a cambered five-bladed 45 W VAWT in an anechoic chamber at different tip speed ratios. The sound pressure level spectrum of VAWT shows that tonal noises such as blade passing frequencies dominate at lower frequencies whereas broadband noise corresponds to all audible ranges of frequencies. This study shows that the major portion of noise from the source is dominated by aerodynamic noises generated due to vortex generation and trailing edge serrations. The research also predicts that dynamic stall is evident in the lower Tip speed ratio (TSR) region making smaller TSR values unsuitable for a quiet VAWT. This paper compares the results of linear aeroacoustic array with a 128-MEMS acoustic camera with higher resolution. The study depicts a 3 dB margin between two systems at lower TSR values. The research approves the usage of the 8 mic linear array for small radius rotary machinery considering the results comparison with a NORSONIC camera and its resolution. These observations serve as a basis for noise reduction and blade optimization techniques.
17
Turner, Jacob M., and Jae Wook Kim. "Aerofoil dipole noise due to flow separation and stall at a low Reynolds number." International Journal of Heat and Fluid Flow 86 (December 2020): 108715. http://dx.doi.org/10.1016/j.ijheatfluidflow.2020.108715.
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18
Lu, Jiaxing, Xiaobing Liu, Yongzhong Zeng, Baoshan Zhu, Bo Hu, and Hong Hua. "Investigation of the Noise Induced by Unstable Flow in a Centrifugal Pump." Energies 13, no. 3 (January 28, 2020): 589. http://dx.doi.org/10.3390/en13030589.
Повний текст джерелаАнотація:
In order to investigate the mechanism and the characteristics of the noise induced by unstable flow in a centrifugal pump, the internal flow characteristics in the pump were numerically researched, and the acoustic pressure fluctuations at the pump inlet and outlet were experimentally investigated. Obvious corresponding relationships between the flow instabilities, the cavitation and the noise were established. It was found that the rotating stall, the backflow, the hump, the occurrence of unstable flow and the cavitation in such a centrifugal pump were effectively detected through the noise, which could help to provide fundamental information on flow instabilities and guarantee safe and steady operating conditions for the system. The recirculation and prewhirl regions in the pump upstream pipe, which were caused by the backflow and the rotation of the impeller, presented the circumferential movement with a spiral shape, causing apparent broadband fluctuations at low frequency band of the acoustic pressure. The backflow and rotating stall could also result in broadband fluctuations of the pump outlet noise, which was distributed from 100 Hz to 150 Hz. Meanwhile, the broadband fluctuations of the pump outlet acoustic pressure distributed in the low frequency range, which was produced by the occurrence of cavitation, moved to the lower frequency band as the flow rate increased. The enhanced broadband fluctuations of the pump inlet and outlet noise distributed from 1 kHz to 6 kHz were caused by the coupling between the cavitation-induced noise and the system-produced noise. The broadband fluctuations of the pump inlet noise distributed between 6 kHz and 9 kHz were regarded as the typical frequency band of cavitation in the centrifugal pump.
19
Zamiri, Ali, Kun Sung Park, Minsuk Choi, and Jin Taek Chung. "Transient Analysis of Flow Unsteadiness and Noise Characteristics in a Centrifugal Compressor with a Novel Vaned Diffuser." Applied Sciences 11, no. 7 (April 2, 2021): 3191. http://dx.doi.org/10.3390/app11073191.
Повний текст джерелаАнотація:
The demands to apply transonic centrifugal compressor have increased in the advanced gas turbine engines. Various techniques are used to increase the aerodynamic performance of the centrifugal compressor. The effects of the inclined leading edges in diffuser vanes of a transonic centrifugal compressor on the flow-field unsteadiness and noise generation are investigated by solving the compressible, three-dimensional, transient Navier–Stokes equations. Diffuser vanes with various inclination angles of the leading edge from shroud-to-hub and hub-to-shroud are numerically modeled. The results show that the hub-to-shroud inclined leading edge improves the compressor performance (2.6%), and the proper inclination angle is effective to increase the stall margin (3.88%). In addition, in this study, the transient pressure variations and radiated noise prediction at the design operating point of the compressor are emphasized. The influences of the inclined leading edges on the pressure waves were captured in time/space domain with different convective velocities. The pressure fluctuation spectra are calculated to investigate the tonal blade passing frequency (BPF) noise, and it is shown that the applied inclination angles in the diffuser blades are effective, not only to improve the aerodynamic performance and stall margin, but also to reduce the BPF noise (7.6 dB sound pressure level reduction). Moreover, it is found that the diffuser vanes with inclination angles could suppress the separation regions and eddy structures inside the passages of the diffuser, which results in reduction of the overall sound pressure level and the broadband noise radiated from the compressor.
20
Liu, Tingrui. "Stall Flutter Suppression for Absolutely Divergent Motions of Wind Turbine Blade Base on H-Infinity Mixed-Sensitivity Synthesis Method." Open Mechanical Engineering Journal 9, no. 1 (September 30, 2015): 752–60. http://dx.doi.org/10.2174/1874155x01509010752.
Повний текст джерелаАнотація:
This paper is devoted to solve the problem of stall flutter suppression for an absolutely divergent blade of small scale wind turbine. The blade is specially designed with absolutely divergent motions for the purpose of determining the most effective methods of active control for stall flutter suppression. A 2-DOF blade section is considered, with a simplified stall nonlinear aerodynamic model being applied. H-infinity mixed-sensitivity synthesis method with a new three-weight regulation is designed to control the time-domain instability of aeroelastic equations, with a third weight being chosen to weight complementary sensitivity for tracking problems and noise attenuation to robust stabilization in H-infinity control. Effects on flutter suppression are investigated based on different structural and external parameters. Apparent effects of H-infinity mixed-sensitivity method are displayed in the paper, when the other common intelligent control methods fail. The research provides a control way for absolutely divergent turbine blade motions.
21
Buchner, Abel-John, Julio Soria, Damon Honnery, and Alexander J. Smits. "Dynamic stall in vertical axis wind turbines: scaling and topological considerations." Journal of Fluid Mechanics 841 (February 27, 2018): 746–66. http://dx.doi.org/10.1017/jfm.2018.112.
Повний текст джерелаАнотація:
Vertical axis wind turbine blades are subject to rapid, cyclical variations in angle of attack and relative airspeed which can induce dynamic stall. This phenomenon poses an obstacle to the greater implementation of vertical axis wind turbines because dynamic stall can reduce turbine efficiency and induce structural vibrations and noise. This study seeks to provide a more comprehensive description of dynamic stall in vertical axis wind turbines, with an emphasis on understanding its parametric dependence and scaling behaviour. This problem is of practical relevance to vertical axis wind turbine design but the inherent coupling of the pitching and velocity scales in the blade kinematics makes this problem of more broad fundamental interest as well. Experiments are performed using particle image velocimetry in the vicinity of the blades of a straight-bladed gyromill-type vertical axis wind turbine at blade Reynolds numbers of between 50 000 and 140 000, tip speed ratios between $\unicode[STIX]{x1D706}=1$ to $\unicode[STIX]{x1D706}=5$, and dimensionless pitch rates of $0.10\leqslant K_{c}\leqslant 0.20$. The effect of these factors on the evolution, strength and timing of vortex shedding from the turbine blades is determined. It is found that tip speed ratio alone is insufficient to describe the circulation production and vortex shedding behaviour from vertical axis wind turbine blades, and a scaling incorporating the dimensionless pitch rate is proposed.
22
Molatudi, Errol, Thokozani Justin Kunene, and Lagouge Kwanda Tartibu. "A Ffowcs Williams-Hawkings numerical aeroacoustic study of varied and fixed-pitch blades of an H-Rotor vertical axis wind turbine." MATEC Web of Conferences 347 (2021): 00013. http://dx.doi.org/10.1051/matecconf/202134700013.
Повний текст джерелаАнотація:
The effects of sound pressure level at two observation positions of a fixed and varied blade pitch angle at Low-Mach unsteady incompressible Reynolds-Average Navier-Stokes flow approach, on an H-rotor Vertical Axis Wind Turbine. The objective of the study is to compare the noise dissipation and output power/energy of the airfoil blades design of the vertical axis wind turbine in residential zones. The Ffowcs Williams-Hawkings (FHWH) techniques were applied to validate the output noise and vortex shedding of the different angles of attacks (AoA). The study postulated that the time history of the calculated sound pressure level at two observers positions: the aeroacoustic, blade vortex interaction noise, flow separations, dynamic stall experience from varied angled of attacks are found to produces less noise and vortex shedding compared to the fixed angle of attack.
23
Xiaohua, Li, Zheng Guo, Grecov Dana, and Zhongxi Hou. "Efficient reduced-order modeling of unsteady aerodynamics under light dynamic stall conditions." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, no. 6 (May 10, 2018): 2141–51. http://dx.doi.org/10.1177/0954410018773628.
Повний текст джерелаАнотація:
In this research, a reduced-order modeling is developed to predict the unsteady aerodynamic forces under light dynamic stall conditions at low-speed regimes. The filtered white Gaussian noise is selected as input signals for computational fluid dynamics solver in order to generate training data, containing the information of reduced frequency and amplitude. Because of the time history influences, the reduced-order modeling combines the Kriging function and recurrence framework together in this approach. An airfoil NACA0012 undergoing pitching motions with different reduced frequency, amplitude, and mean angle of attack is designed to illustrate the methodology. The developed model can predict the lift, drag, and moment coefficients in seconds on a single-core computer processor. To reduce the prediction errors between reduced-order modeling predictions and computational fluid dynamics simulations, the aerodynamic loads in static conditions are applied as initial inputs. The predictions via the proposed approach are in agreement with the results using a high precision computational fluid dynamics solver over the designed ranges of amplitude and reduced frequency, which is suitable for engineering applications, such as fluid-structure interaction, and aircraft design optimizations.
24
Turner, Jacob M., and Jae Wook Kim. "Effect of spanwise domain size on direct numerical simulations of airfoil noise during flow separation and stall." Physics of Fluids 32, no. 6 (June 1, 2020): 065103. http://dx.doi.org/10.1063/5.0009664.
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Luo, Hongying, Ran Tao, Jiandong Yang, and Zhengwei Wang. "Influence of Blade Leading-Edge Shape on Rotating-Stalled Flow Characteristics in a Centrifugal Pump Impeller." Applied Sciences 10, no. 16 (August 14, 2020): 5635. http://dx.doi.org/10.3390/app10165635.
Повний текст джерелаАнотація:
Rotating stall, which is a common phenomenon in turbomachinery, strongly relates to the flow rate condition. In centrifugal impellers, rotating stall was induced by the incidence angle on blade leading-edge at partial-load. The blade leading-edge shape also influences the rotating stall because of the subtle change of local flow-field. In this study, the influence of blade leading-edge shape on rotating-stalled flow characteristics was studied in a six-blade centrifugal pump impeller. The stall pattern was “alternating”: Three passages were stalled, three passages were well-behaved, and the stalled and well-behaved passages occurred alternately. The stalled flow characteristics can be studied without the interruption of stall cell movement. Four types of blade leading-edge (blunt, sharp, ellipse, and round) were numerically compared based on the initial typical impeller and the numerical–experimental verification. The numerical comparison shows that the leading-edge shape has a strong influence on the stalled flow pattern, velocity, pressure, turbulence kinetic energy, and flow-induced noise inside impellers. The blunt and sharp leading-edge impellers had a similar internal pattern; the ellipse and round leading-edge impellers were also similar in the internal flow-field. Pressure pulsation analysis showed more obvious differences among these impellers. The main frequency and the pulsation peak–peak values were completely different because of the slight leading-edge shape differences. It revealed the impact of leading-edge geometry on the transient flow-field change under the same incidence angle conditions. It also provided reference for influencing or controlling the rotating stall by blade profile design.
26
Li, Jia, Xu Dong, Dakun Sun, Yuqing Wang, Chunwang Geng, and Xiaofeng Sun. "Stability Enhancement and Noise Reduction of an Axial Compressor with Foam Metal Casing Treatment." Aerospace 9, no. 10 (October 21, 2022): 628. http://dx.doi.org/10.3390/aerospace9100628.
Повний текст джерелаАнотація:
Foam metal is a foam-like substance with a high porosity; it has been used in flow control, vibration abatement, and acoustic absorption, mainly based on its physical properties. The aim of the current paper is to investigate the effect of foam metal casing treatments on the stability and acoustic level of a low-speed axial flow compressor. The experimental results show that the casing treatment improves the stall margin by 14.9%, without any efficiency loss. In terms of noise, the SPL of the tonal noise at the third order of BPF is reduced by 3.2 dB, while the SPL of the broadband noise is reduced up to 2.4 dB. The comparison in evolutions of the tip structure in a smooth casing condition and with a casing treatment indicates that the casing treatment affects the origination and the development of the tip leakage vortex. The working mechanism is also discussed.
27
Yang, Yongfei, Wei Li, Weidong Shi, Yuanfeng Ping, Yang Yang, and Lei Wang. "Numerical investigation on the unstable flow at off-design condition in a mixed-flow pump." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 233, no. 7 (February 28, 2019): 849–65. http://dx.doi.org/10.1177/0957650919833892.
Повний текст джерелаАнотація:
The mixed-flow pump is wildly used in industrial and agricultural fields, and the requirements for its stability become more and more restricted with the improvement of the capacities. When the pump is operated under part-loading conditions, unstable characteristic like rotating stall happens and brings intensive vibration and noise. To reveal the internal unstable flow characteristics in mixed-flow pump, unsteady numerical simulation is conducted under different flow rates in the current research. The secondary flow and the vortex induced by the unsteady flow in the pump, which vary with the change of the flow rate, are analyzed according to the simulation results. Pressure fluctuation in different parts of the impeller is numerically predicted and correlated to the rotating stall propagation process. With the reduction of the flow discharge, a critical flow rate (0.6 Qdes in the current model pump) is found related to the rotating stall inception. Unstable vortex structure is found in part of the flow passages of the impeller under the stall inception stage; 0.56 Qdes is the flow rate related to the deep rotating stall under which stable stall vortexes are found in each flow passage of the impeller. Three types of pressure fluctuation characteristics representing different flow field pattern in the impeller are found. When the pump is working at designed flow rate, the pressure fluctuation is regular with the dominant frequency being the rotation frequency fs of the rotor. At the stall inception condition, when the stall core appears in the flow passages of the impeller in turn, the amplitude of the pressure fluctuation is increased and the dominant frequency is changed to a low-frequency signal. When the flow rate is reduced below deep stall condition, owning to the reflux from the guide vane and the intensive rotor–stator interaction, the blade passing frequency of the guide vane fb2 becomes the dominant frequency. Finally, unsteady characteristics of the flow field under stall inception condition are analyzed to demonstrate the propagation process of the rotating stall. The stall vortex is found to propagate from the stalled flow passage to the next, through the tip area of the blade leading edge. During the propagation process, the first vortex shrinks and disappears gradually, while the second vortex grows continuously, and the third vortex shows up at the vanishment of the first stall vortex. This research provides detailed information for the unstable flow especially related to rotating stall evolution with the variation of the operating flow rate of the mixed-flow pump with guide vane.
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Tryfonidis, M., O. Etchevers, J. D. Paduano, A. H. Epstein, and G. J. Hendricks. "Prestall Behavior of Several High-Speed Compressors." Journal of Turbomachinery 117, no. 1 (January 1, 1995): 62–80. http://dx.doi.org/10.1115/1.2835644.
Повний текст джерелаАнотація:
High-speed compressor data immediately prior to rotating stall inception are analyzed and compared to stability theory. New techniques for the detection of small-amplitude rotating waves in the presence of noise are detailed, and experimental and signal processing pitfalls discussed. In all nine compressors examined, rotating stall precedes surge. Prior to rotating stall inception, all the machines support small-amplitude (< 1 percent of fully developed stall) waves traveling about the circumference. Traveling wave strength and structure are shown to be a strong function of corrected speed. At low speeds, a ∼0.5 times shaft speed wave is present for hundreds of rotor revolutions prior to stall initiation. At 100 percent speed, a shaft speed rotating wave dominates, growing as stall initiation is approached (fully developed rotating stall occurs at about 1/2 of shaft speed). A new, two-dimensional, compressible hydrodynamic stability analysis is applied to the geometry of two of the compressors and gives results in agreement with data. The calculations show that, at low corrected speeds, these compressors behave predominantly as incompressible machines. The wave that first goes unstable is the 1/2 shaft frequency mode predicted by the incompressible Moore–Greitzer analysis and previously observed in low-speed compressors. Compressibility becomes important at high corrected speeds and adds axial structure to the rotating waves. At 100 percent corrected speed, one of these hitherto unrecognized compressible modes goes unstable first. The rotating frequency of this mode is constant and predicted to be approximately coincident with shaft speed at design. Thus, it is susceptible to excitation by geometric nonuniformities in the compressor. This new understanding of compressor dynamics is used to introduce the concept of traveling wave energy as a real time measure of compressor stability. Such a wave energy-based scheme is shown consistently to give an indication of low stability for significant periods (100–200 rotor revolutions) before stall initiation, even at 100 percent corrected speed.
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Watkins, Joseph, and Abdessalem Bouferrouk. "The Effects of a Morphed Trailing-Edge Flap on the Aeroacoustic and Aerodynamic Performance of a 30P30N Aerofoil." Acoustics 4, no. 1 (March 3, 2022): 248–67. http://dx.doi.org/10.3390/acoustics4010015.
Повний текст джерелаАнотація:
This paper presents initial results on the aeroacoustic and aerodynamic effects of morphing the trailing-edge flap of the 30P30N aerofoil, over five flap deflections (5–25°), at an 8° angle of attack and a Reynolds number of Re=9.2×105. The Ffowcs-Williams–Hawkings acoustic analogy estimates the far-field noise, whilst the flow field is solved using URANS with the four-equation Transition SST model. Aerodynamic and aeroacoustic simulation data for the 30P30N’s full configuration compare well with experimental results. A Courant number (C) ≤ 1 should be used for resolving tonal noise, whilst a C of up to 4 is sufficient for broadband noise. Sound pressure level results show an average 11% reduction in broadband noise across all flap deflections and frequencies for the morphed configuration compared with the conventional, single-slotted flap. The morphed flap eliminates the multiple tonal peaks observed in the conventional design. Beyond 15° flap deflection, the morphing flap achieves higher stall angles, but with increased drag, leading to a maximum reduction of 17% in Cl/Cd ratio compared with the conventional flap. The methodology reported here for the 30P30N is a quick tool for initial estimates of the far-field noise and aerodynamic performance of a morphing flap at the design stage.
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Spalart, P. R., and D. R. Bogue. "The role of CFD in aerodynamics, off-design." Aeronautical Journal 107, no. 1072 (June 2003): 323–29. http://dx.doi.org/10.1017/s0001924000013634.
Повний текст джерелаАнотація:
Abstract We discuss the status, trends and long-term ambitions of Computational Fluid Dynamics (CFD) when applied away from the design point or concept, and therefore in the historically weak areas of CFD. This includes both undesirable flight conditions, such as stall, and undesirable products of the flow, such as noise. All pose the great challenge of turbulence, and accuracy is as dependent on the ideas behind the turbulence treatment as it is on computing power. A measured shift from Reynolds-averaged representations to large-eddy simulations will take place. Empiricism, both turbulence and engineering related, will recede only step by step over many years. Yet, CFD will make full use of every increase in computer power of this century. Increasingly, CFD will compete with flight tests, not just with wind tunnels, and will be validated by flight tests. Integration with other disciplines will allow us to predict crucial phenomena such as flutter, sonic fatigue, and pilot-induced oscillations. A gap will remain at any time between the phenomena amenable to a ‘grand challenge’ calculation and those amenable to a fully CFD-based design process, because certification involves thousands of conditions. The highest demand currently is in community and cabin noise for which industrial-accuracy methods are non-existent. On the other hand, gratifying progress has occurred in the area of stall and spin.
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Genç, Gamze, Kemal Koca, and Mustafa Serdar Genç. "Unsteady aerodynamics over surface of a chambered airfoil at stall angle and low Reynolds number." EPJ Web of Conferences 269 (2022): 01016. http://dx.doi.org/10.1051/epjconf/202226901016.
Повний текст джерелаАнотація:
The proposal of this paper is clear to reveal and understand the unsteady flow characteristics over the surface of chambered airfoil operating especially at low Reynolds numbers by detecting boundary layer separation and laminar separation bubble (LSB). Experiments including smoke-wire technique for flow visualization, velocity measurement via hot-wire sensor and quasi-wall shear stress measurement by means of the hot-film sensor have been performed over the suction surface of NACA 4412 airfoil at Reynolds number of 5x104 and angle of attack of 14°. Experiments indicate that the airfoil at a stall angle exhibits the bistable characteristics over the suction surface because of the unsteady bubble bursting at low Reynolds numbers. That is, either laminar flow separates from the leading-edge of the airfoil owing to a dominant adverse pressure gradient (APG) or it does not separate along downstream. It is also noted that unsteady boundary layer formation may affect the flow characteristics by changing airfoil’s stability appreciably, causing the periodic fluctuations with the occurring bubble bursting and the leading edge and trailing edge vortex merging. This may conclude undesirable problems such as noise, vibration and flutter for the flight vehicles and wind turbines.
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Lee, Gwang-Se, Cheolung Cheong, Su-Hyun Shin, and Sung-Soo Jung. "A case study of localization and identification of noise sources from a pitch and a stall regulated wind turbine." Applied Acoustics 73, no. 8 (August 2012): 817–27. http://dx.doi.org/10.1016/j.apacoust.2012.03.001.
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Redonnet, Stéphane, and Thomas G. Schmidt. "Experimental investigation of the laminar boundary layer vortex-shedding noise by an airfoil within a closed-vein wind tunnel." International Journal of Aeroacoustics 21, no. 8 (November 2022): 658–83. http://dx.doi.org/10.1177/1475472x221136882.
Повний текст джерелаАнотація:
This study concerns the experimental characterization of trailing edge noise, the understanding of which is crucial for mitigating acoustic pollution across major industries. An aeroacoustic experiment is carried out using a closed-vein wind tunnel to investigate the laminar boundary layer vortex-shedding (LBL-VS) noise of a symmetric NACA0021 airfoil in low Reynolds number flows (Re ≤ 163,500). Steady aerodynamic and acoustic measurements are performed, with numerous conditions covered (flow velocity from 10 m/s to 24.5 m/s, airfoil incidence from −10° to 10°). The aerodynamic results reveal that, in the pre-stall regime, the airfoil’ suction side exhibits both a laminar separation bubble (LSB) and a trailing edge detached flow – which both make LBL-VS noise likely to occur. The acoustic results reveal that, when at low speed and moderate incidence, the airfoil emits one to two tones, which can be both attributed to LBL-VS noise. In particular, their respective frequency is seen to scale as the 0.8th power of the flow velocity, whereas varying linearly with the incidence. At higher speeds, these two tones vanish to the profit of other, more intense tonal emissions, whose frequency does not scale with the velocity nor the incidence. These tones are attributed to resonance effects coming from a retroaction of the reverberant environment onto the LBL-VS noise emission, which then locks-on to some of the duct resonant frequencies via an acoustic feedback loop. Revealing indirectly the presence of the pre-existing LBL-VS noise, these resonant tones emerge only when the flow velocity and incidence obey specific conditions, namely a roughly linear relationship.
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Hay, N., J. S. B. Mather, and R. Metcalfe. "Fan Blade Selection for Low Noise Part 1: Design Philosophy." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power Engineering 203, no. 3 (August 1989): 149–54. http://dx.doi.org/10.1243/pime_proc_1989_203_021_02.
Повний текст джерелаАнотація:
It has been known for many years that the broadband noise of rotating machinery is dependent on the condition of the boundary layers on the lifting surfaces. Designs with high efficiencies and clean flow have mainly produced low noise levels. These units have generally used high technology blading, with low inlet velocities and minimal separated flow. In the application of machines in industry, however, many are subject to inlet flow distortion and turbulence. These produce changes to the flow pattern around the blades which may have a relatively insignificant effect on the aerodynamics of the machine but almost completely destroy its acoustic performance. The design method described by Hay, Metcalfe and Reizes (15) allows the designer to pitch the operating point well away from stall. Thus low-response blading can be used for those installations whose flow conditions cannot be improved. This method is further developed in this paper using some correlations from McKenzie's work (17). The application of the method to the design of a low noise fan in the presence of a ±10 per cent perturbation on inlet velocity is given in way of illustration of the approach. In Part 2 of this paper (to be published later) it is hoped to demonstrate the validity of the design philosophy presented here with test results from fans designed according to this philosophy.
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Guo, Meng, Cheng Liu, Qingdong Yan, Zhifang Ke, Wei Wei, and Juan Li. "Evaluation and Validation of Viscous Oil Cavitation Model Used in Torque Converter." Applied Sciences 11, no. 8 (April 18, 2021): 3643. http://dx.doi.org/10.3390/app11083643.
Повний текст джерелаАнотація:
Hydraulic torque converter is widely used in transmission units as it is able to provide variable speed and torque ratio, isolate vibration, and absorb shock. The pursuit of a highly packed power unit requires a high capacity/speed torque converter, consequently resulting in a higher risk for cavitation and severe performance degradation, noise, vibration, and even failure. Existing cavitation models generally focus on water, and the empirical parameters are not suitable for the cavitation prediction of torque converter which utilizes high viscosity oil as its working medium. This paper focused on the influence of parameters on the performance and cavitation characteristics of torque converter. A full flow passage geometry and different computational fluid dynamics (CFD) models with cavitation were developed to predict torque converter fluid behavior by resolving Reynolds-averaged Navier–Stokes equations using finite volume method (FVM). The numerical results indicated that nuclei volume fraction, vaporization coefficient, mean nucleation site radius, and maximum density ratio have great influences on the cavitation behavior. These parameters altered the degree of cavitation and the pressure distribution on the surface of stator blades, and affected the stall performance such as stall capacity factor and torque ratio. The cavitation model was then modified to improve calculation accuracy. The test results showed that the prediction error under stall operating condition was decreased from 6.7% to 2%. This study provides insight on the influences of the empirical parameters on both internal cavitation behavior as well as overall hydrodynamic performance.
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Bertagnolio, Franck, Helge Aa Madsen, Andreas Fischer, and Christian Bak. "Corrigendum to “A semi-empirical airfoil stall noise model based on surface pressure measurements” [J. Sound Vib. 387 (2017) 127–162]." Journal of Sound and Vibration 424 (June 2018): 378. http://dx.doi.org/10.1016/j.jsv.2018.01.053.
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Valldosera Martinez, Robert, Frederico Afonso, and Fernando Lau. "Aerodynamic Shape Optimisation of a Camber Morphing Airfoil and Noise Estimation." Aerospace 9, no. 1 (January 15, 2022): 43. http://dx.doi.org/10.3390/aerospace9010043.
Повний текст джерелаАнотація:
In order to decrease the emitted airframe noise by a two-dimensional high-lift configuration during take-off and landing performance, a morphing airfoil has been designed through a shape design optimisation procedure starting from a baseline airfoil (NLR 7301), with the aim of emulating a high-lift configuration in terms of aerodynamic performance. A methodology has been implemented to accomplish such aerodynamic improvements by means of the compressible steady RANS equations at a certain angle of attack, with the objective of maximising its lift coefficient up to equivalent values regarding the high-lift configuration, whilst respecting the imposed structural constraints to guarantee a realistic optimised design. For such purposes, a gradient-based optimisation through the discrete adjoint method has been undertaken. Once the optimised airfoil is achieved, unsteady simulations have been carried out to obtain surface pressure distributions along a certain time-span to later serve as the input data for the aeroacoustic prediction framework, based on the Farassat 1A formulation, where the subsequent results for both configurations are post-processed to allow for a comparative analysis. Conclusively, the morphing airfoil has proven to be advantageous in terms of aeroacoustics, in which the noise has been reduced with respect to the conventional high-lift configuration for a comparable lift coefficient, despite being hampered by a significant drag coefficient increase due to stall on the morphing airfoil’s trailing edge.
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Oehme, Felix, Michael Sorg, and Andreas Fischer. "Detection and localization of flow separation on wind turbines by means of unsteady thermographic flow visualization." Journal of Physics: Conference Series 2265, no. 2 (May 1, 2022): 022101. http://dx.doi.org/10.1088/1742-6596/2265/2/022101.
Повний текст джерелаАнотація:
Abstract For the first time, a thermographic detection and localization of turbulent flow separation on an operating wind turbine is presented and verified. Flow separation on wind turbine rotor blades causes power reduction, structural loads and increased noise emissions. In contrast to established methods for stall detection, the presented infrared thermographic measurement approach is non-invasive, in-process capable and provides a high spatial resolution. With respect to the state of the art for thermographic stall detection in wind tunnel experiments, the thermal surface response to unsteady inflow conditions is evaluated for measurements on an operating wind turbine, in order to achieve unambiguous thermographic features for the detection of flow separation. The evaluation of the thermodynamic response behavior shows a clear detection of flow separation by means of temperature fluctuation maxima in the regions of flow transition as well as an increasing temperature fluctuation within the separated flow region. In addition, a geometric assignment is conducted which enables a localization of the separation point with an uncertainty of 0.6% of the chord length. The detection and localization of flow separation is verified by means of tufts visualization.
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de O. Falca˜o, A. F., L. C. Vieira, P. A. P. Justino, and J. M. C. S. Andre´. "By-Pass Air-Valve Control of an OWC Wave Power Plant." Journal of Offshore Mechanics and Arctic Engineering 125, no. 3 (July 11, 2003): 205–10. http://dx.doi.org/10.1115/1.1576815.
Повний текст джерелаАнотація:
The paper deals with the numerical simulation of the performance of an oscillating-water-column (OWC) wave power plant equipped with a by-pass valve whose role is to prevent the turbine flow rate from exceeding the stall-free operating conditions. Continuous and step-wise valve area changes are considered, the second case corresponding to multi-element design. The adequacy of the valve and of its control is assessed through the gain in annual electrical energy and the total number of required valve strokes. The following items are separately analyzed: (i) number of (identical) valve elements; (ii) valve response time; (iii) signal noise level in chamber air-pressure measurements due to large-eddy turbulence; (iv) valve’s control algorithm.
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Vasista, Srinivas, Johannes Riemenschneider, Ralf Keimer, Hans Peter Monner, Felix Nolte, and Peter Horst. "Morphing Wing Droop Nose with Large Deformation: Ground Tests and Lessons Learned." Aerospace 6, no. 10 (October 2, 2019): 111. http://dx.doi.org/10.3390/aerospace6100111.
Повний текст джерелаАнотація:
A design for a new high lift system that features a morphing wing leading edge “droop nose” has the potential to generate high lift coefficients whilst mitigating airframe noise emissions. This seamless, continuous, and stepless flexible droop nose potentially offers improvements to stall and compressor requirements for an internally-blown active Coandă trailing edge flap. A full-scale, span-trimmed three-dimensional droop nose was manufactured and ground-tested based on results obtained from new design synthesis tools. A new component of the droop nose is the hybrid fiberglass-elastomeric skin that is tailored in stiffness to meet morphing curvature requirements and spanwise bending resistance. A manufacturing concept of the novel skin was established that led to an adequate manufacturing quality. The skin was driven and supported by two optimized kinematic ribs and conventional actuators and overall shape results show good agreement apart from the region closest to the leading edge. Kinematic trajectory measurements showed that the kinematics met the target trajectories well, with and without the influence of the skin, and it was deemed that the error in curvature is due to a higher than expected skin stiffness in the hybrid layer. Calculated actuator torque levels and strain measurements corroborate this inference. The lessons learned show that means of adjustment post-assembly are needed, and a reduction of torque, energy and a better curvature distribution may be achieved if the skin at the spar junction is allowed to move relative to the main wing. Careful aerodynamic, structural, actuation and manufacturing trade-off studies would be needed to determine the overall performance benefit.
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Malkhede, D. N., H. C. Dhariwal, and M. C. Joshi. "ON OPTIMIZATION OF THE PID GOVERNOR FOR DIESEL ENGINE." Mathematical Modelling and Analysis 7, no. 1 (June 30, 2002): 135–50. http://dx.doi.org/10.3846/13926292.2002.9637186.
Повний текст джерелаАнотація:
In a diesel engine, governor is indispensable for ensuring that the engine maintains a certain speed under various load conditions, that the engine speed does not exceed a certain speed as a protection against self‐destruction or stall. Also, speed fluctuations resulting from poor governing, lead to vibrations, noise, wear and tear and increased level of soot. Therefore it is desirable to have minimum speed fluctuations under all engine‐operating conditions. Inspite of many limitations, most of the existing engines still use simple mechanical governor providing proportional control only. Electronic governors can provide a more flexible P (proportional), I (integral), and D (derivative) control under all speeds and loads. So far no work is reported on optimizing the controller parameters using the analytical approach. In the present work turbo charged diesel engine is analytically modeled based on Krutov's approach for the control analysis. Attempts have been made to optimize controller parameters. The criterion for minimizing the engine speed fluctuations is met by minimizing the Integral Squared Error in engine speed. The parameters obtained have been used to study the engine speed response. The results have shown remarkable improvement in the engine speed fluctuations.
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Hill, S. D., R. L. Elder, and A. B. McKenzie. "Application of casing treatment to an industrial axial-flow fan." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 212, no. 4 (June 1, 1998): 225–33. http://dx.doi.org/10.1243/0957650981536754.
Повний текст джерелаАнотація:
This paper deals with an experimental investigation into the influence of a vaned recess casing treatment on the performance of an industrial-type axial-flow fan with a hub-tip ratio of 0.4. The treatment has been tested in a variety of configurations relative to the fan, with an emphasis on the amount of fan blade tip exposure to the treatment. Two sets of blading, one of which is of the fully reversible type, have been investigated. Detailed flow measurements have been carried out with a slanted hot wire probe to provide an insight into the operation of the device and into the nature of the rotating stall in the solid casing configuration. Strain gauges have been employed to enable blade stresses to be recorded and an in-duct microphone to enable comparative tests on fan noise has also been used.
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Wang, Wendong, Lixin Zhang, Xiao Ma, Zhizheng Hu, and Yongchun Yan. "Experimental and Numerical Simulation Study of Pressure Pulsations during Hose Pump Operation." Processes 9, no. 7 (July 16, 2021): 1231. http://dx.doi.org/10.3390/pr9071231.
Повний текст джерелаАнотація:
An adventitious flow field has a great impact on the operational reliability of pumps; therefore, it is important to study pump flow characteristics to reduce the noise, vibration, and cavitation performance of pumps. To study the pressure fluctuation characteristics of the hose pump, a three-dimensional two-way fluid structure coupling model of the hose pump was established. The transient structural module, fluid flow (fluent) module, and system coupling module of ANSYS Workbench 19.0 were used to simulate the unsteady multiple working conditions of the hose pump. The accuracy and reliability of the calculation results from the fluid solid coupling simulation were verified via experimentation. The results show that the roller pass frequency is the main frequency of the pressure fluctuation at the outlet of the hose pump. When the plane of the deformation recovery area is small, the pressure pulsation amplitude is large, and the outlet pressure and speed are large. Due to the irregular backflow of the fluid, stall zones of different sizes form, the outlet pressure is closer to a sinusoid when there is no pressure. The higher the rotating speed is, the faster the pressure roller leaving the hose, the higher the pressure pulsation, and the larger the stall zone. Therefore, the best way to reduce the pressure pulsation in the pump is to optimize the geometry of the pressure roller and change the outlet angle of the hose.
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Emagbetere, J. O., and P. A. Kuale. "Investigation of Harmonics in Power Generating Systems." Advanced Materials Research 18-19 (June 2007): 99–106. http://dx.doi.org/10.4028/www.scientific.net/amr.18-19.99.
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This paper investigates harmonics in power systems especially harmonics produced by synchronous generators as well as those by distributed generation systems, particularly these days when private generating systems are on the increase in Nigeria. For the work done so far, we found that some generators have near square waves, and these are characterized by their odd harmonics. An investigation of the harmonic emf waves conducted shows that these generators produces harmonic alternating mmf’s and fluxes. All harmonic fluxes produce emfs which are undesirable. The effect of these harmonics results in additional losses, vibration and noise, interferences, and very often stall motors. However the useful torque of a machine is usually produced by the fundamental flux wave which is a pure sine wave. The work is on-going. The waveforms are being analyzed so as to determine the full spectrum of the harmonics present in each case and subsequently investigate their effects in telecommunication systems including the present day GSM.
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Sharma, P. B., Y. P. Jain, and D. S. Pundhir. "A Study of Some Factors Affecting the Performance of a Contra-Rotating Axial Compressor Stage." Proceedings of the Institution of Mechanical Engineers, Part A: Power and Process Engineering 202, no. 1 (February 1988): 15–21. http://dx.doi.org/10.1243/pime_proc_1988_202_003_02.
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An experimental investigation of the performance of a contra-rotating stage is reported. The influence of factors such as speed ratio of the two rotors, rotor stagger, pitch-chord ratio and axial spacing between the rotors is examined from tests on a 0.66 hub-tip ratio compressor. The study reveals that the performance of a contra-rotating stage is affected by all these factors. Axial spacing between the rotors and the speed ratio of the rotors both exhibit a strong influence on the stalling behaviour of the stage. It has been found that in a stage with close axial gap, rotating stall on the first rotor is suppressed if the second rotor is contra-rotated at a speed 50 per cent faster than the first rotor. This unique advantage of contra-rotation is not obtained if the axial gap is large. Measurements of sound pressure level are also reported to highlight the high noise problems associated with a contra-rotating stage.
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Phung, Trung-Nghia, Huy-Khoi Do, Van-Tao Nguyen, and Quang-Vinh Thai. "Eigennoise Speech Recovery in Adverse Environments with Joint Compensation of Additive and Convolutive Noise." Advances in Acoustics and Vibration 2015 (November 3, 2015): 1–9. http://dx.doi.org/10.1155/2015/170183.
Повний текст джерелаАнотація:
The learning-based speech recovery approach using statistical spectral conversion has been used for some kind of distorted speech as alaryngeal speech and body-conducted speech (or bone-conducted speech). This approach attempts to recover clean speech (undistorted speech) from noisy speech (distorted speech) by converting the statistical models of noisy speech into that of clean speech without the prior knowledge on characteristics and distributions of noise source. Presently, this approach has still not attracted many researchers to apply in general noisy speech enhancement because of some major problems: those are the difficulties of noise adaptation and the lack of noise robust synthesizable features in different noisy environments. In this paper, we adopted the methods of state-of-the-art voice conversions and speaker adaptation in speech recognition to the proposed speech recovery approach applied in different kinds of noisy environment, especially in adverse environments with joint compensation of additive and convolutive noises. We proposed to use the decorrelated wavelet packet coefficients as a low-dimensional robust synthesizable feature under noisy environments. We also proposed a noise adaptation for speech recovery with the eigennoise similar to the eigenvoice in voice conversion. The experimental results showed that the proposed approach highly outperformed traditional nonlearning-based approaches.
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Qu, Huajie, Chendong Liu, Lei Zhang, Jianjun Qu, and Baoyu Song. "A Longitudinal-Bending Hybrid Linear Ultrasonic Motor and Its Driving Characteristic." Shock and Vibration 2022 (January 6, 2022): 1–14. http://dx.doi.org/10.1155/2022/5701014.
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As a new type of driver, linear ultrasonic motor (LUSM) is widely used in the high-tech field because of its low speed, high thrust, low noise, and no electromagnetic interference. However, as an actuator used in microdevices, most of the existing LUSMs are large in size and not compact in structure. In order to overcome these limitations, a new structure of linear ultrasonic motor’s stator is developed in this paper. The stator is similar to a tuning fork structure, which is divided into three parts: two driving feet, two driving legs, and the driving body. By using the first-order longitudinal vibration mode of the whole stator and the unique partial second-order bending vibration mode of the driving legs to achieve vibration mode degeneracy, a mode hybrid linear ultrasonic motor that is easy to miniaturize is proposed. Its working principle is analyzed. The dynamic analysis of the stator is carried out by using finite element software. The structure dimension of the stator and the driving frequency under the working mode are determined. At the same time, the feasibility of driving feet synthesizing elliptical motion is verified theoretically and experimentally. In addition, the LUSM test setup is built. The effects of driving frequency and Vpp on stator stall force and average velocity are studied. The results show that the maximum stall force can reach 99 mN, and the average velocity of the motor is 88.67 mm/s with Vpp = 320 V and driving frequency 80.2 kHz. The proposed LUSM is appropriate for use in occasions with quick return characteristics, like the controlling valve or nozzle of the printer. The research results provide guidance for the stator design of the linear ultrasonic motor.
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Daniele, Elia, Matthias Schramm, Christof Rautmann, Mehdi Doosttalab, and Bernhard Stoevesandt. "An extension of a strong viscous–inviscid coupling method for modeling the effects of vortex generators." Wind Engineering 43, no. 2 (June 14, 2018): 175–89. http://dx.doi.org/10.1177/0309524x18780390.
Повний текст джерелаАнотація:
The aim of this work is to provide insights into the advantages and the limitations of the extension of a strong viscous–inviscid interactive code for modeling the effects of vortex generators, with focus on the calibration and validation for wind turbine airfoils. The proposed methodology relies on the approach proposed by other authors in the past and introduces an alternative formulation for the lag dissipation within the integral boundary-layer equations whose effects on the numerical prediction are evaluated. Besides the verification of the aeronautical test cases, particular attention is devoted to the validation of the results for several airfoils commonly used in wind turbine design. A blind test for airfoils from an industrial test case is conducted as well. Results show that the maximum lift coefficient can be well predicted by the present implementation, whereas the angle of maximum lift is a little higher than in wind tunnel measurements. Apart from that, the drag coefficients of airfoils with vortex generators cannot be predicted by the current implementation, but it is expected that the maximum lift and the stall angle of attack are more important in the design phase, since they determine power, loads, and noise.
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HO, WEN-HSIEN, YENMING J. CHEN, YUZHEN ZHANG, YANYUN TAO, and HSIN-WEN KUO. "HEART DISEASES DETECTION FROM NOISY RECORDINGS OF SMARTPHONE DEVICES." Journal of Mechanics in Medicine and Biology 18, no. 04 (June 2018): 1850039. http://dx.doi.org/10.1142/s0219519418500392.
Повний текст джерелаАнотація:
This paper aims to develop an algorithm to detect heart diseases through ordinary smartphones without additional equipment for cost accessibility. Among various vital signs emitted by organs, sounds can be easily observed and carry ample information. However, these sounds are small and noisy. Detecting anomalies involves great challenges in signal processing. This study presents a novel method that overcomes noises to estimate cardiovascular health. We use time-scale techniques in time series analysis to extract disease traits and suppress excessive ambient noises. Using datasets from PhysioNet, our model achieved a nearly 100% accuracy in heart disease diagnosis. Our approach also performs well under excessive noises for diseases producing heart murmurs. With heavy noise contaminated signals, training accuracy still closed to 100%, and the testing accuracy still remained around 84%.
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Contell Asins, Conchin, Volker Landersheim, Dominik Laveuve, Seiji Adachi, Michael May, Jens-David Wacker, and Julia Decker. "Analysis and Design of a Leading Edge with Morphing Capabilities for the Wing of a Regional Aircraft—Gapless Chord- and Camber-Increase for High-Lift Performance." Applied Sciences 11, no. 6 (March 19, 2021): 2752. http://dx.doi.org/10.3390/app11062752.
Повний текст джерелаАнотація:
In order to contribute to achieving noise and emission reduction goals, Fraunhofer and Airbus deal with the development of a morphing leading edge (MLE) as a high lift device for aircraft. Within the European research program “Clean Sky 2”, a morphing leading edge with gapless chord- and camber-increase for high-lift performance was developed. The MLE is able to morph into two different aerofoils—one for cruise and one for take-off/landing, the latter increasing lift and stall angle over the former. The shape flexibility is realised by a carbon fibre reinforced plastic (CFRP) skin optimised for bending and a sliding contact at the bottom. The material is selected in terms of type, thickness, and lay-up including ply-wise fibre orientation based on numerical simulation and material tests. The MLE is driven by an internal electromechanical actuation system. Load introduction into the skin is realised by span-wise stringers, which require specific stiffness and thermal expansion properties for this task. To avoid the penetration of a bird into the front spar of the wing in case of bird strike, a bird strike protection structure is proposed and analysed. In this paper, the designed MLE including aerodynamic properties, composite skin structure, actuation system, and bird strike behaviour is described and analysed.