scholarly journals Pressure Fluctuations Characteristics of the Stilling Basin with a Negative Step

2021 ◽  
Author(s):  
Guibing Huang ◽  
Mingjun Diao ◽  
Lei Jiang ◽  
Chuan’ai Wang ◽  
Wang Jia
Keyword(s):  
Incident Angle ◽  
Pressure Coefficient ◽  
Pressure Fluctuations ◽  
Jet Impingement ◽  
Dominant Frequency ◽  
Geometric Parameters ◽  
Step Height ◽  
Type Ii ◽  
Fluctuating Pressure ◽  
Stilling Basin

Fluctuating pressure is the main cause of the floor fatigue of the stilling basin with a negative step. Despite investigations of stilling basin with a negative step conducted by many researchers, there is not enough information about the influence of the geometric parameters on fluctuating pressure on the floor. In the present study, fluctuating pressure on the floor of the stilling basin with a negative step was systematically investigated by a total of 85 model tests. The results show that the fluctuating pressure coefficient Cp’ has a process of rapid increase and decrease, and then decreases slowly until it becomes stable, and the maximum fluctuating pressure coefficient Cp’max lies in the reattachment zone rather than in the jet impingement area for Type II-jump. The dominant frequency of the fluctuating pressure on the floor shows a decreasing trend along stilling basin. With the increase of the step height, the Cp’max presents decreasing trend but X*0 where the Cp’max occurs increasing trend. While there has on obvious regularity between incident angle and Cp’. Finally, according to the fitting of test data, an empirical formula to calculate Cp’max is developed. These research results provide reference for the design of stilling basin with a negative step in engineering applications.

scholarly journals Fluctuating Characteristics of the Stilling Basin with a Negative Step Based on Hilbert-Huang Transform

Water ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 2673
Author(s):  
Wang Jia ◽  
Mingjun Diao ◽  
Lei Jiang ◽  
Guibing Huang
Keyword(s):  
Jet Impingement ◽  
Dominant Frequency ◽  
Fluctuating Pressure ◽  
Hilbert Huang Transform ◽  
Time Frequency ◽  
Pressure Signal ◽  
Stilling Basin ◽  
Impingement Zone ◽  
Marginal Spectrum ◽  
Stilling Basins

The violent fluctuation of hydrodynamic pressure in stilling basins is an important factor threatening the safety of the bottom plates of stilling basins, and plays an important role in the safe operation of stilling basins. In order to deeply understand the fluctuating characteristics of stilling basins, the fluctuating pressure signal of a stilling basin bottom plate is processed by the Hilbert-Huang transform method through a hydraulic model test. In this paper, three signal decomposition methods are used to decompose the pulsating pressure signal. A Hilbert transform is used to select the component with the best decomposition effect. The time-frequency-amplitude diagram of the pulsating pressure signal is obtained by Hilbert transform, and its time-frequency characteristics are discussed in depth. The analysis results are as follows: (a) the decomposition results from the CEEMD method are orthogonal and complete. The HHT method is suitable for processing fluctuating pressure signals. (b) With an increase in IMF decomposition order, the signal frequency band becomes narrow, the Hilbert spectrum amplitude decreases and the pulsating pressure energy decreases. The decomposition of the fluctuating pressure signal into components of different scales shows that the turbulence is composed of multiple scales of vortices, reflecting the vortex structure in the turbulence. (c) The jet impingement zone of the drop bucket stilling basin is near x/L = 0.075. The dominant frequency and marginal spectrum energy of the jet impingement zone are very prominent, and the marginal spectrum energy is mostly concentrated within 5.0 Hz. (d) At different drop height and different flow energy ratio, the fluctuation in the dominant frequency of fluctuating pressure decreases, the dominant frequency of the head of the stilling basin is larger, the dominant frequency of the middle and rear parts tends to be stable, and the dominant frequency is finally stabilized at about 1.0 Hz. This paper attempts to use the HHT method to process the fluctuating pressure signal, and the results provide a new discussion method for exploring the fluctuating pressure characteristics of hydraulic structures.

scholarly journals Distribution of Pressure Fluctuations in a Prototype Pump Turbine at Pump Mode

2014 ◽  
Vol 6 ◽  
pp. 923937 ◽  
Author(s):  
Yuekun Sun ◽  
Zhigang Zuo ◽  
Shuhong Liu ◽  
Jintao Liu ◽  
Yulin Wu
Keyword(s):  
Mass Flow ◽  
Pressure Fluctuations ◽  
Dominant Frequency ◽  
Pump Mode ◽  
Pump Turbine ◽  
Guide Vanes ◽  
Path Direction ◽  
Mass Flow Rates ◽  
Operating Points ◽  
Spiral Casing

Pressure fluctuations are very important characteristics in pump turbine's operation. Many researches have focused on the characteristics (amplitude and frequencies) of pressure fluctuations at specific locations, but little researches mentioned the distribution of pressure fluctuations in a pump turbine. In this paper, 3D numerical simulations using SSTk − ω turbulence model were carried out to predict the pressure fluctuations distribution in a prototype pump turbine at pump mode. Three operating points with different mass flow rates and different guide vanes’ openings were simulated. The numerical results show how pressure fluctuations at blade passing frequency (BPF) and its harmonics vary along the whole flow path direction, as well as along the circumferential direction. BPF is the first dominant frequency in vaneless space. Pressure fluctuation component at this frequency rapidly decays towards upstream (to draft tube) and downstream (to spiral casing). In contrast, pressure fluctuations component at 3BPF spreads to upstream and downstream with almost constant amplitude. Amplitude and frequencies of pressure fluctuations also vary along different circumferential locations in vaneless space. When the mass flow and guide vanes’ opening are different, the distribution of pressure fluctuations along the two directions is different basically.

scholarly journals Energy Dissipation in Solid Roller Bucket and Controlled Stilling Basin for Ogee Stepped Spillway

2019 ◽  
Vol 8 (4) ◽  
pp. 2109-2112
Keyword(s):  
Energy Dissipation ◽  
Laboratory Experiments ◽  
Ideal Condition ◽  
Stepped Spillway ◽  
Type Ii ◽  
Dimensional Parameter ◽  
Stilling Basin ◽  
Sequent Depth ◽  
Tail Water ◽  
The Ideal

Hydraulic jump type II stilling basin is generally preferred as an energy dissipator for ogee spillway but it is uneconomical due to longer structure. On the other hand, roller bucket uses relatively shorter structure over a sloping apron or horizontal stilling basin. In this study, an attempt has been made to evaluate the performance of an ogee profile stepped spillway in combination with solid roller bucket and stilling basin type II for energy dissipation. Laboratory experiments are performed on a physical working model of ogee profile stepped spillway at discharge ranging from 0.0032 to 0.0069 m3 /s for a head of 1.5m, 4m & 7m and the results compared for energy dissipation (non-dimensional parameter (y c / h) = 0.69). The model results show that stepped spillway model without v-notch achieves 92.40 % energy dissipation. Thus this model is found to be more suitable to acquire the ideal condition of sequent depth and tail water depth in stilling basin for all the discharges.

The Baffle Blocks Effects of Pressure Characteristics on USBR III Basin Floor

2012 ◽  
Vol 212-213 ◽  
pp. 821-825
Author(s):  
Keyvan Nasiri ◽  
Mohammad Reza Kavianpour ◽  
Siavash Haghighi
Keyword(s):  
Energy Dissipation ◽  
Hydraulic Jump ◽  
Pressure Fluctuations ◽  
Power Spectra ◽  
Low Frequency ◽  
Dominant Frequency ◽  
Energy Dissipation Rate ◽  
Tension And Compression ◽  
Basin Floor ◽  
Sequent Depth

The principle of energy dissipation in stilling basin is based on hydraulic jump formation. Due to the inherent fluctuating characteristic of the hydraulic jump, basin floor is subjected to variations of pressure, resulting in unstableness due to uplift forces. To increase the efficiency of the stilling basins and improve the energy dissipation rate, one or two rows of baffle blocks are applied on the basin floor. Causing a forced hydraulic jump, tension and compression forces are exerted by pressure fluctuations of rotating roller zone of hydraulic jump. In this investigation, to observe the impacts of baffle blocks on pressure fluctuations on basin floor, a standard USBR basin model type III was constructed, and then a second row of blocks was added to the basin. A set of pressure tubes was fixed along the axis of the basin to measure the static and dynamic pressures on basin floor. The results were expressed in dimensionless parameters including C-p, C+p, C’p, Cp. Also, power spectra of pressure fluctuations were calculated. The results show a decreasing trend in root mean square of pressure fluctuations as distancing from toe of jump along the basin with and without baffle blocks. Also, mean pressure increases when water jet strokes the basin then decreases under roller zone of jump and increases again after sequent depth. The spectral analysis indicates that the dominant frequency is between 10 rad/s and 35 rad/s and pressure fluctuations have low frequency characteristics.

Aerodynamic Forces on Multiple Unit Trains in Cross Winds

2009 ◽  
Vol 131 (10) ◽  
Author(s):  
Christopher J. Baker ◽  
Mark Sterling
Keyword(s):  
Pressure Fluctuations ◽  
Decomposition Analysis ◽  
Aerodynamic Characteristics ◽  
Scale Model ◽  
Fluctuating Pressure ◽  
Time Histories ◽  
Multiple Unit ◽  
The Mean ◽  
Proper Orthogonal ◽  
Natural Wind

This paper describes the results of wind tunnel tests that were carried out to measure the aerodynamic characteristics of an electrical multiple unit (EMU) vehicle in a cross wind. The measurements were made on a 1/30 scale model of the Class 365 EMU in a simulation of the natural wind. The time histories of surface pressures were measured at a large number of points over the vehicle from which the aerodynamic characteristics and force coefficients were determined. This paper describes the complex fluctuating pressure field over the vehicle, through a consideration of the mean and fluctuating pressure coefficients and their spectra, and through a proper orthogonal decomposition analysis, which identifies the major modes of this distribution. The mean, fluctuating, and extreme aerodynamic side and lift forces are also discussed. It is shown that the flow pattern around the vehicle is dominated by large windward roof corner pressure fluctuations.

Experimental Study on Pressure Fluctuations in the Boundary Layer of an Axisymmetric Body

2011 ◽  
Vol 66-68 ◽  
pp. 1488-1493
Author(s):  
Hong Xiao ◽  
Chao Gao ◽  
Zhen Kun Ma
Keyword(s):  
Boundary Layer ◽  
Experimental Study ◽  
Mach Number ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Axisymmetric Body ◽  
Pressure Measurements ◽  
Fluctuating Pressure ◽  
Frequency Domains ◽  
Dynamic Pressure Measurements

The characteristics of the fluctuating pressure in the boundary layer of an axisymmetric body have been investigated experimentally using dynamic pressure measurements and Schlieren photograghs. Data were acquired at subsonic and super-sonic Mach numbers. The angles of attack ranged from 0° to 5°. Pressure signals were measured simultaneously in several positions along the model and were analyzed both in the time and frequency domains. The Mach number shows the relevant influence on . Furthermore, the pressure fluctuations’ level decreases with the increasing of Mach number except M=1.15. And it is shown that, the location along the axis of the model and the angles of attack have small effect on pressure fluctuations.

Investigation of Supercritical Flow and Shape of Flip Bucket Spillways on Coefficients of Dynamic Pressure

2020 ◽  
Vol 143 (6) ◽  
Author(s):  
Hessam Vatandoust ◽  
Hamidreza Yarmohammadi ◽  
Mohammadreza Kavianpour
Keyword(s):  
Froude Number ◽  
Pressure Fluctuation ◽  
Dynamic Pressure ◽  
Pressure Coefficient ◽  
Pressure Fluctuations ◽  
Experimental Studies ◽  
Flow Speed ◽  
Middle Part ◽  
Statistical Characteristics ◽  
Pressure Coefficients

Abstract Pressure fluctuation is one of the major turbulent flow characteristics. It may cause crucial problems for hydraulic structures. This research is based on experimental studies, and it focuses on the measurements of pressure fluctuations along flip bucket spillways with different geometrical characteristics. The function of the flip bucket spillway is discharging floods from reservoir dams which are energy storage source measurements of dynamic pressures on three different models of flip buckets that were performed for this investigation. Pressure fluctuation of the flip buckets have been measured within a range of Froude numbers from 5 to 13 (Fr = u/gy, where u is the flow speed, y is the depth, and g is 9.81 m/s2). Statistical characteristics of pressure fluctuations, the location, and the values of maximum and minimum fluctuations have also supplemented the study. The results show that the coefficients of pressure fluctuations (Cp = RMS/(0.5(u2/g)) where RMS is the root-mean-square of pressure fluctuation, u is the flow speed, and g is 9.81 m/s2) reduce as the Froude number (Fr) of flow increases, except a maximum Froude number. Pressure coefficients increase along the flip bucket with incremental mutations in the transformation area of the flip bucket. In the middle part of the flip bucket spillway, pressure coefficient values decrease. Additionally, as B/r (B is the width of the flip bucket and r is the radius of the flip bucket) ratio increases, pressure coefficients become larger and this process continues along the flip bucket.

scholarly journals Analysis of minimal and maximal pressures, uncertainty and spectral density of fluctuating pressures beneath classical hydraulic jumps

2020 ◽  
Vol 20 (5) ◽  
pp. 1909-1921
Author(s):  
Seyed Nasrollah Mousavi ◽  
Davood Farsadizadeh ◽  
Farzin Salmasi ◽  
Ali Hosseinzadeh Dalir ◽  
Daniele Bocchiola
Keyword(s):  
Spectral Density ◽  
Large Scale ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Dominant Frequency ◽  
Standard Uncertainty ◽  
Hydraulic Jumps ◽  
Stilling Basins ◽  
Density Analysis ◽  
Real Scale

Abstract Knowledge of extreme pressures and fluctuations within stilling basins is of the utmost importance, as they may cause potential severe damages. It is complicated to measure the fluctuating pressures of hydraulic jumps in real-scale structures. Therefore, little information is available about the pressure fluctuations in the literature. In this paper, minimal and maximal pressures were analyzed on the flat bed of a stilling basin downstream of an Ogee spillway. Attention has been focused on dimensionless pressures related to the low and high cumulative probabilities of occurrence (P*0.1% and P*99.9%), respectively. The results were presented based on the laboratory-scale experiments. These parameters for the relatively high Froude numbers have not been investigated. The total standard uncertainty for the dimensionless mean pressures (P*m) was obtained around 1.87%. Spectral density analysis showed that the dominant frequency in the classical hydraulic jumps was about 4 HZ. Low-frequency of pressure fluctuations indicated the existence of large-scale vortices. In the zone near the spillway toe, P*0.1% reached negative values of around −0.3. The maximum values of pressure coefficients, namely |CP0.1%|max and CP99.9%max, were achieved around 0.19 and 0.24, respectively. New original expressions were proposed for P*0.1% and P*99.9%, which are useful for estimating extreme pressures.

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