On the generation mechanisms of low-frequency synchronous pressure pulsations in a simplified draft-tube cone

2022 ◽  
Vol 93 ◽  
pp. 108912
Author(s):  
Mohammad Hossein Khozaei ◽  
Arthur Favrel ◽  
Kazuyoshi Miyagawa
Keyword(s):  
Draft Tube ◽  
Low Frequency ◽  
Pressure Pulsations ◽  
Generation Mechanisms

Aeroacoustic analysis of slat tones

2021 ◽  
Vol 263 (1) ◽  
pp. 5650-5663
Author(s):  
Hasan Kamliya Jawahar ◽  
Syamir Alihan Showkat Ali ◽  
Mahdi Azarpeyvand
Keyword(s):  
Wavelet Transform ◽  
Surface Pressure ◽  
Wavelet Coefficient ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Stream Velocity ◽  
High Lift ◽  
Unsteady Surface Pressure ◽  
Slat Noise ◽  
Generation Mechanisms

Experimental measurements were carried out to assess the aeroacoustic characteristics of a 30P30N high-lift device, with particular attention to slat tonal noise. Three different types of slat modifications, namely slat cove filler, serrated slat cusp, and slat finlets have been experimentally examined. The results are presented for an angle of attack of α = 18 at a free-stream velocity of U = 30 m/s, which corresponds to a chord-based Reynolds number of Re = 7 x 10. The unsteady surface pressure near the slat region and far-field noise were made simultaneously to gain a deeper understanding of the slat noise generation mechanisms. The nature of the low-frequency broadband hump and the slat tones were investigated using higher-order statistical approaches for the baseline 30P30N and modified slat configurations. Continuous wavelet transform of the unsteady surface pressure fluctuations along with secondary wavelet transform of the broadband hump and tones were carried out to analyze the intermittent events induced by the tone generating resonant mechanisms. Stochastic analysis of the wavelet coefficient modulus of the surface pressure fluctuations was also carried out to demonstrate the inherent differences of different tonal frequencies. An understanding into the nature of the noise generated from the slat will help design the new generation of quite high-lift devices.

Monitoring the parameters of a reactor by low-frequency pressure pulsations

1981 ◽  
Vol 51 (2) ◽  
pp. 512-516
Author(s):  
V. I. Vlasov ◽  
S. A. Mokrushin ◽  
V. P. Radchenko ◽  
V. V. Selin ◽  
A. A. Artamonov ◽  
...  
Keyword(s):  
Low Frequency ◽  
Pressure Pulsations

Comparison of Axial Water and Air Injections in the Draft Tube of a Francis Turbine for RVR Mitigation

2021 ◽  
Author(s):  
Subodh Khullar ◽  
Krishna M. Singh ◽  
Michel J. Cervantes ◽  
Bhupendra K. Gandhi
Keyword(s):  
Pressure Pulsation ◽  
Draft Tube ◽  
Water Injection ◽  
Air Injection ◽  
Flow Instabilities ◽  
Pressure Recovery ◽  
Francis Turbine ◽  
Tube Flow ◽  
Pressure Pulsations ◽  
Jet Injection

Abstract The presence of excessive swirl at the runner outlet in Francis turbines operating at part load leads to the development of flow instabilities such as the rotating vortex rope (RVR). The presence of RVR causes severe pressure pulsations, power swings, and fatigue damage in the turbine unit. Air and water injection in the draft tube have been reported to reduce the detrimental effects of RVR formation in the Francis turbines. Air injection is one of the oldest and most widely used methods. In contrast, water jet injection is a relatively new methodology. The present work reports the numerical simulations performed to compare the respective effectiveness of these methods to mitigate the RVR and the related flow instabilities. The efficacy of the two methods has been compared based on the pressure pulsations and pressure recovery in the draft tube cone. The results show that the air and water injection influence the draft tube flow field in different ways. Both air and water injection led to a reduction in pressure pulsation magnitudes in the draft tube cone. However, the air injection led to a negative pressure recovery while the water injection improved the draft tube action.

Model and Prototype Draft Tube Pressure Pulsations

1996 ◽  
pp. 994-1003 ◽  
Author(s):  
Vladimir Kercan ◽  
Marin Bajd ◽  
Vesko Djelić ◽  
Andrej Lipej ◽  
Dragica Jošt
Keyword(s):  
Draft Tube ◽  
Pressure Pulsations

Mechanism of Fast Transition of Pressure Pulsations in the Vaneless Space of a Model Pump-Turbine During Runaway

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Xiaoxi Zhang ◽  
Wei Zeng ◽  
Yongguang Cheng ◽  
Zhiyan Yang ◽  
Qiuhua Chen ◽  
...  
Keyword(s):  
Transient Flow ◽  
Characteristic Curve ◽  
Three Dimensional ◽  
Low Frequency ◽  
Vortex Structures ◽  
Pressure Pulsations ◽  
Pump Turbine ◽  
Whole Process ◽  
Time Variations ◽  
Flow Vortex

The pressure pulsations in the vaneless space of pump-turbines are extremely intense and always experience rapid time variations during transient scenarios, causing structural vibrations and even more serious accidents. In this study, the mechanism behind the rapid time variations of the vaneless space pressure pulsations in a model pump-turbine during runaway was analyzed through three-dimensional (3D) numerical simulations. These results show that the high-frequency pressure pulsation components originating from rotor–stator interactions (RSI) are dominant during the whole process. These components fluctuate significantly in frequency when the working point goes through the S-shaped region of the characteristic curve, with the amplitudes increasing. Meanwhile, some low-frequency pulsations are also enhanced and become obvious. These features can be attributed to the transitions of the inter blade vortex structures (IBVSs) to the forward flow vortex structures (FFVSs) and the back flow vortex structures (BFVSs) at the impeller entrance, when the pump-turbine operates in the region with S-shaped characteristics. The FFVSs mainly cause decreases in frequency and introduce low-frequency pulsations, while the BFVSs are responsible for the unstable fluctuations. These findings contribute to the understanding of how transient flow patterns evolve and may provide new ideas about avoiding severe pressure pulsations caused by rotating stalls in the pump-turbine during transient scenarios.

The numerical simulation of low frequency pressure pulsations in the high-head Francis turbine

2015 ◽  
Vol 111 ◽  
pp. 197-205 ◽  
Author(s):  
A.V. Minakov ◽  
D.V. Platonov ◽  
A.A. Dekterev ◽  
A.V. Sentyabov ◽  
A.V. Zakharov
Keyword(s):  
Numerical Simulation ◽  
Low Frequency ◽  
Francis Turbine ◽  
Pressure Pulsations ◽  
High Head

Statistical Considerations on Pressure Pulses from a Cavitating Venturi

1986 ◽  
Vol 200 (6) ◽  
pp. 381-387
Author(s):  
S Li ◽  
Y Zhang ◽  
F G Hammitt
Keyword(s):  
Closed Loop ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Resonant Interaction ◽  
Statistical Characteristics ◽  
Pressure Pulsations ◽  
Cavitation Inception ◽  
Flow Noise ◽  
Pressure Pulses ◽  
Liquid Portion

Pressure pulses emitted from cavitating venturi flows are measured and investigated statistically. The results show that according to the degree of cavitation, the overall pressure pulsations consist of different combinations of three components, that is basic flow noise, cavitation pulses and low-frequency pressure fluctuations, due primarily to overall loop characteristics. The statistical characteristics are presented and compared. It is believed that the low-frequency fluctuations result from a resonant interaction between the cavitation ‘cloud’ and the liquid portion of the closed loop. They occur near cavitation inception, reach a maximum at a particular cavitation number, σres, then gradually disappear for increased σ. Their frequency is basically constant for all σ. An empirical-theoretical model of this behaviour is presented.

Unsteady regimes and pressure pulsations in draft tube of a model hydro turbine in a range of off-design conditions

2018 ◽  
Vol 91 ◽  
pp. 410-422 ◽  
Author(s):  
Ivan Litvinov ◽  
Sergey Shtork ◽  
Evgeny Gorelikov ◽  
Andrey Mitryakov ◽  
Kemal Hanjalic
Keyword(s):  
Draft Tube ◽  
Pressure Pulsations ◽  
Hydro Turbine ◽  
Unsteady Regimes

Generation Mechanisms of Low-Frequency Centrifugal Fan Noise

AIAA Journal ◽  
10.2514/2.610 ◽  
1999 ◽  
Vol 37 (10) ◽  
pp. 1173-1179 ◽  
Author(s):  
K.-R. Fehse ◽  
W. Neise
Keyword(s):  
Low Frequency ◽  
Centrifugal Fan ◽  
Fan Noise ◽  
Generation Mechanisms

scholarly journals Ray tracing of whistler-mode chorus elements: implications for generation mechanisms of rising and falling tone emissions

2013 ◽  
Vol 31 (4) ◽  
pp. 665-673 ◽  
Author(s):  
K. Yamaguchi ◽  
T. Matsumuro ◽  
Y. Omura ◽  
D. Nunn
Keyword(s):  
Ray Tracing ◽  
Low Frequency ◽  
Equatorial Region ◽  
Lower Hybrid ◽  
Wave Pulse ◽  
Generation Region ◽  
Field Lines ◽  
Generation Mechanisms ◽  
Tone Generation ◽  
Lower Hybrid Resonance

Abstract. Using a well-established magnetospheric very-low-frequency (VLF) ray tracing method, in this work we trace the propagation of individual rising- and falling-frequency elements of VLF chorus from their generation point in the equatorial region of the magnetosphere through to at least one reflection at the lower-hybrid resonance point. Unlike recent work by Bortnik and co-workers, whose emphasis was on demonstrating that magnetospheric hiss has its origins in chorus, we here track the motion in the equatorial plane of the whole chorus element, paying particular regard to movement across field lines, rotation, and compression or expansion of the wave pulse. With a generation point for rising chorus at the equator, it was found the element wave pulse remained largely field aligned in the generation region. However, for a falling tone generation point at 4000 km upstream from the equator, by the time the pulse crosses the equator the wavefield had substantial obliquity, displacement, and compression, which has substantial implications for the theory of falling chorus generation.

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