scholarly journals Suppression of low-frequency pressure pulsations in an open jet wind tunnel by corner vortex generators

AIP Advances ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 065306
Author(s):  
Ling Jin ◽  
Haisheng Sun ◽  
Yubiao Jiang ◽  
Yong Liang ◽  
Junlong Zhang
Keyword(s):  
Wind Tunnel ◽  
Low Frequency ◽  
Vortex Generators ◽  
Pressure Pulsations ◽  
Corner Vortex

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

Effect on Water Leak of Tiled Roofs by Wind Flow Over Japanese Residence

2010 ◽  
Author(s):  
Satoru Okamoto
Keyword(s):  
Wind Tunnel ◽  
Low Frequency ◽  
Video Camera ◽  
Wind Flow ◽  
Leak Test ◽  
Low Velocity ◽  
Artificial Rainfall ◽  
Water Leak ◽  
Series Of Experiments ◽  
Set Up

This paper describes a water leak test of roof tiles. The 100 roof tiles were set up on 10 lines and 10 rows on the pitched roof in the downstream of the flow from the wind tunnel. The flow velocity was increased gradually from the low velocity to the high velocity, and the effects of the wind on the roof tiles were investigated by the water leak test. The situation of the water leak test was filmed by video camera. Two accelerometers were simultaneously used. The roof tiles which showed significant vibration at any velocity were found in a series of experiments and the accelerometers were attached to the two neighboring roof tiles on the model roof. The water leak phenomena in the experiment by using the artificial rainfall apparatus are discussed in this paper. Some mechanisms with relatively large amplitudes at low-frequency vibrations, which caused water leak phenomena were made clear.

scholarly journals Multidimensional System Identification and Active Vibration Control of a Piezoelectric-Based Sting System Used in Wind Tunnel

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Yi Yu ◽  
Xing Shen ◽  
Yun Huang
Keyword(s):  
Control System ◽  
System Identification ◽  
Wind Tunnel ◽  
Vibration Control ◽  
Active Vibration Control ◽  
Low Frequency ◽  
Vibration Monitoring ◽  
Multidimensional System ◽  
Monitoring Method ◽  
Active Vibration

In wind tunnel tests, the cantilever sting is usually used to support aircraft models because of its simple structure and low aerodynamic interference. However, in some special conditions, big-amplitude and low-frequency vibration would occur easily on the model not only in the pitch direction but also in the yaw direction, resulting in inaccurate data and even damage of the supporting structure. In this paper, aiming at suppressing the vibration in pitch and yaw plane, a multidimensional system identification and active vibration control system on the basis of piezoelectric actuators is established. A vibration monitoring method based on the strain-displacement transformation (SDT) matrix is proposed, which can transform strain signals into vibration displacements. The system identification based on chirp-Z transform (CZT) is applied to improve the adaptability and precision of the building process for the system model. After that, the hardware platform as well as the software control system based on the classical proportional-derivative (PD) algorithm is built. A series of experiments are carried out, and the results show the exactness of the vibration monitoring method. The system identification process is completed, and the controller is designed. Vibration control experiments verify the effectiveness of the controller, and the results indicate that vibrations in pitch and yaw directions are attenuated apparently. The spectrum power is reduced over 14.8 dB/Hz, which prove that the multidimensional identification and active vibration control system has the capability to decline vibration from different directions.

scholarly journals Mitigating Large Vibrations of Stayed Cables in Wind and Rain Hazards

2020 ◽  
Vol 2020 ◽  
pp. 1-10 ◽  
Author(s):  
Hung Vo-Duy ◽  
Cung H. Nguyen
Keyword(s):  
Experimental Investigation ◽  
Wind Tunnel ◽  
Significant Role ◽  
Low Frequency ◽  
Vortex Flows ◽  
Complex Mechanism ◽  
High Wind ◽  
Wind Speeds ◽  
Cable Vibrations

This paper presents an experimental investigation of stayed cable vibrations in dry-wind and rain-wind coupling hazards. To mitigate large vibrations of the cable, the use of spiral wires wrapped around the cable is proposed. By testing two cable models in a wind tunnel in dry and rain conditions for different yaw angles and wind speeds, the effectiveness of using the spiral wires to mitigate large vibrations is clarified. Finally, the paper provides a further understanding of the complex mechanism of wind-induced and rain-wind-induced vibrations. It is found that the low-frequency vortex flows in the wake play a significant role in the excitation of large responses of the cable in high wind speeds. The spiral wires dismiss these low-frequency flows and then reduce the large vibrations.

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.

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