Pressure oscillations with ultra-low frequency induced by vortical flow inside Francis turbine draft tubes

2022 ◽  
Vol 51 ◽  
pp. 101908
Author(s):  
Chen Geng ◽  
Ying Li ◽  
Yoshinobu Tsujimoto ◽  
Michihiro Nishi ◽  
Xianwu Luo
Keyword(s):  
Low Frequency ◽  
Vortical Flow ◽  
Francis Turbine ◽  
Pressure Oscillations ◽  
Draft Tubes

Pressure Oscillations with Ultra-Low Frequency Induced by Vortical Flow Inside Francis Turbine Draft Tubes

2021 ◽  
Author(s):  
Chen Geng ◽  
Ying Li ◽  
Yoshinobu Tsujimoto ◽  
Michihiro Nishi ◽  
Xianwu Luo
Keyword(s):  
Low Frequency ◽  
Vortical Flow ◽  
Francis Turbine ◽  
Pressure Oscillations ◽  
Draft Tubes

scholarly journals Comparisons of vortical flow and cavitation inside a Francis turbine with different draft tubes

2021 ◽  
Vol 774 (1) ◽  
pp. 012146
Author(s):  
Chen Geng ◽  
Ruizhi Zhang ◽  
Yoshinobu Tsujimoto ◽  
Michihiro Nishi ◽  
Xianwu Luo
Keyword(s):  
Vortical Flow ◽  
Francis Turbine ◽  
Draft Tubes

Dynamic Stability of a Water Brake Dynamometer

1998 ◽  
Vol 120 (1) ◽  
pp. 89-96 ◽  
Author(s):  
R. A. Van den Braembussche ◽  
H. Malys
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Lumped Parameter Model ◽  
Stable Operation ◽  
Pressure Oscillations ◽  
Lumped Parameter ◽  
Flow Oscillations ◽  
Brake Dynamometer ◽  
Low Torque ◽  
Frequency Variations

A lumped parameter model to predict the high frequency pressure oscillations observed in a water brake dynamometer is presented. It explains how the measured low frequency variations of the torque are a consequence of the variation in amplitude of the high frequency flow oscillations. Based on this model, geometrical modifications were defined, aiming to suppress the oscillations while maintaining mechanical integrity of the device. An experimental verification demonstrated the validity of the model and showed a very stable operation of the modified dynamometer even at very low torque.

Paper 14: Acoustic Detection of Cavitation

1966 ◽  
Vol 181 (1) ◽  
pp. 1-8 ◽  
Author(s):  
I. S. Pearsall
Keyword(s):  
High Frequency ◽  
Critical Frequency ◽  
Low Frequency ◽  
Francis Turbine ◽  
Frequency Noise ◽  
Performance Tests ◽  
Acoustic Detection ◽  
Cavitation Noise ◽  
Further Development ◽  
Onset Of Cavitation

The onset of cavitation in a hydraulic machine can be determined visually and its effect on performance by performance tests. It would be convenient to have an alternative method that required neither transparent sections nor expensive tests. Initial tests have been made measuring noise over a frequency range of 20 c/s-20 kc/s in one-third octave bands, on a number of pumps and turbines. An accelerometer attached to the casing was used. The tests indicated that, generally, the onset of cavitation was accompanied by a rise in the high-frequency noise, whilst the low-frequency noise increased as the cavitation developed. A maximum of cavitation noise was reached before the efficiency and load fell off. In some cases difficulty was experienced because blade cavitation was drowned by noise caused by other cavitation, such as the vortex in a Francis turbine. It also appears that the noise following the onset of cavitation is at the frequency which is used as a critical frequency in accelerated erosion tests. Further development of techniques is required, but the initial tests are encouraging.

scholarly journals Low-frequency arterial pressure fluctuations do not reflect sympathetic outflow: gender and age differences

1998 ◽  
Vol 274 (4) ◽  
pp. H1194-H1201 ◽  
Author(s):  
J. Andrew Taylor ◽  
Todd D. Williams ◽  
Douglas R. Seals ◽  
Kevin P. Davy
Keyword(s):  
Arterial Pressure ◽  
Low Frequency ◽  
Total Activity ◽  
Sympathetic Outflow ◽  
Pressure Oscillations ◽  
Young Males ◽  
Young Females ◽  
Sympathetic Nervous ◽  
Mayer Wave ◽  
Older Males

Low-frequency arterial pressure oscillations (Mayer waves) have been proposed as an index of vascular sympathetic outflow. However, cross-sectional differences in these pressure oscillations may not reflect different levels of sympathetic nervous outflow in humans. Three groups of healthy subjects with characteristically different sympathetic nervous outflow were studied: young females ( n = 10, 18–28 yr), young males ( n = 11, 18–29 yr), and older males ( n = 13, 60–72 yr). Average R-R interval, arterial pressures, and systolic pressure variability at the Mayer wave frequency (0.05–0.15 Hz) did not differ among the three groups. Diastolic pressure Mayer wave variability was similar in young females vs. young males (39 ± 10 vs. 34 ± 5 mmHg2) and lower in older males vs. young males (14 ± 2 mmHg2; P < 0.05). In contrast, muscle sympathetic activity was lowest in young females (892 ± 249 total activity/min) and highest in older males (3,616 ± 528 total activity/min; both P < 0.05 vs. young males: 2,505 ± 285 total activity/min). Across the three groups, arterial pressure Mayer wave variability did not correlate with any index of sympathetic activity. Our results demonstrate that arterial pressure Mayer wave amplitude is not a surrogate measure of vascular sympathetic outflow.

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

scholarly journals Three-dimensional instabilities in compressible flow over open cavities

2008 ◽  
Vol 599 ◽  
pp. 309-339 ◽  
Author(s):  
GUILLAUME A. BRÈS ◽  
TIM COLONIUS
Keyword(s):  
Compressible Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Low Frequency ◽  
Vortical Flow ◽  
Cavity Flows ◽  
Two Dimensional ◽  
Mean Flow ◽  
Aspect Ratios ◽  
Open Cavities

Direct numerical simulations are performed to investigate the three-dimensional stability of compressible flow over open cavities. A linear stability analysis is conducted to search for three-dimensional global instabilities of the two-dimensional mean flow for cavities that are homogeneous in the spanwise direction. The presence of such instabilities is reported for a range of flow conditions and cavity aspect ratios. For cavities of aspect ratio (length to depth) of 2 and 4, the three-dimensional mode has a spanwise wavelength of approximately one cavity depth and oscillates with a frequency about one order of magnitude lower than two-dimensional Rossiter (flow/acoustics) instabilities. A steady mode of smaller spanwise wavelength is also identified for square cavities. The linear results indicate that the instability is hydrodynamic (rather than acoustic) in nature and arises from a generic centrifugal instability mechanism associated with the mean recirculating vortical flow in the downstream part of the cavity. These three-dimensional instabilities are related to centrifugal instabilities previously reported in flows over backward-facing steps, lid-driven cavity flows and Couette flows. Results from three-dimensional simulations of the nonlinear compressible Navier–Stokes equations are also reported. The formation of oscillating (and, in some cases, steady) spanwise structures is observed inside the cavity. The spanwise wavelength and oscillation frequency of these structures agree with the linear analysis predictions. When present, the shear-layer (Rossiter) oscillations experience a low-frequency modulation that arises from nonlinear interactions with the three-dimensional mode. The results are consistent with observations of low-frequency modulations and spanwise structures in previous experimental and numerical studies on open cavity flows.

Combustion Oscillations in Bluff Body Stabilized Diffusion Flames With Variable Length Inlet

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
M. Madanmohan ◽  
S. Pandey ◽  
A. Kushari ◽  
K. Ramamurthi
Keyword(s):  
Heat Release ◽  
Phase Angle ◽  
Bluff Body ◽  
Diffusion Flames ◽  
Combustion Process ◽  
Low Frequency ◽  
Pressure Oscillations ◽  
Pipe Length ◽  
Entry Length ◽  
Low Frequency Oscillations

This paper describes the results of an experimental study to understand the influence of inlet flow disturbances on the dynamics of combustion process in bluff body stabilized diffusion flames of liquid petroleum gas and air. The results show the influence of weak disturbances created by the change in incoming pipe length on the amplitude of pressure oscillations and the phase angle between pressure and heat release. It is seen that the phase delay increases as the entry length increases. The rms value of pressure, however, generally falls with the increase in length. The phase angle is seen to be in the second quadrant, showing that the heat release oscillations damp the pressure oscillations. Therefore, the decrease in the phase angle results in the reduction in damping and hence an increase in pressure fluctuations. The dominant frequencies of combustion oscillations are found to be the low frequency oscillations, and the frequency of oscillations increases with a decrease in the inlet pipe length and an increase in the flow Reynolds number. It is suggested that such low frequency oscillations are driven by vortex shedding at the wake of the bluff body, which energizes the diffusion and mixing process.

Amplitude-Limiting Feedback Control of Combustion Instability With a High-Momentum Air Jet

2004 ◽  
Author(s):  
Jong Ho Uhm ◽  
Sumanta Acharya
Keyword(s):  
Frequency Modulation ◽  
Low Frequency ◽  
Threshold Level ◽  
Acoustic Mode ◽  
Effective Control ◽  
Pressure Amplitude ◽  
High Momentum ◽  
Pressure Oscillations ◽  
Air Jet ◽  
Duty Cycles

A new strategy that integrates low-frequency modulation of a high-momentum air-jet with amplitude feedback is presented for control of combustion oscillations in a swirl-stabilized spray combustor. The oscillations in the combustor of interest are dominated by an acoustic mode (235 Hz) with a low frequency (13 Hz) bulk-mode (of the upstream cavity) superimposed. An effective strategy for control is shown to be achieved through the use of a concept which utilizes low bandwidth modulation of a high-momentum air-jet that penetrates into the regions of positive Rayleigh index. It is shown that with a low frequency modulation (5 Hz) of the high momentum air-jet, the pressure oscillations can be reduced significantly (by a factor of nearly 6). Further improvement in control is achieved with an amplitude-limiting feedback strategy, in which, the valve opening and closing of the control air-jet is driven by the pressure amplitude relative to a specified threshold. The goal of the controller is to maintain pressure oscillations below the pre-set threshold level. With this strategy, the valve frequency and duty cycle are automatically adjusted based on the amplitude of the pressure signal. It is observed that modulation frequencies are typically in the range of 5–30 Hz (although higher frequencies, as high as 130 Hz, are needed occasionally). Duty cycles less than 50% are required for effective control. The amplitude-limiting feedback controller is shown to combine the benefits of low-bandwidth actuation, low-duty cycles, and greater reductions in pressure oscillations.

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