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.

The Cavitation-Induced Pressure Fluctuations in a Mixed-Flow Pump under Impeller Inflow Distortion

Machines ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 326
Author(s):  
Huiyan Zhang ◽  
Fan Meng ◽  
Yunhao Zheng ◽  
Yanjun Li
Keyword(s):  
Frequency Domain ◽  
Pressure Fluctuation ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Pressure Sensors ◽  
Mixed Flow ◽  
Guide Vanes ◽  
Time Frequency ◽  
Critical Cavitation ◽  
Flow Pump

To reduce cavitation-induced pressure fluctuations in a mixed-flow pump under impeller inflow distortion, the dynamic pressure signal at different monitoring points of a mixed-flow pump with a dustpan-shaped inlet conduit under normal and critical cavitation conditions was collected using high-precision digital pressure sensors. Firstly, the nonuniformity of the impeller inflow caused by inlet conduit shape was characterized by the time–frequency-domain spectra and statistical characteristics of pressure fluctuation at four monitoring points (P4–P7) circumferentially distributed at the outlet of the inlet conduit. Then, the cavity distribution on the blade surface was captured by a stroboscope. Lastly, the characteristics of cavitation-induced pressure fluctuation were obtained by analyzing the time–frequency-domain spectra and statistical characteristic values of dynamic pressure signals at the impeller inlet (P1), guide vanes inlet (P2), and guide vanes outlet (P3). The results show that the flow distribution of impeller inflow is asymmetric. The pav values at P4 and P6 were the smallest and largest, respectively. Compared with normal conditions, the impeller inlet pressure is lower under critical cavitation conditions, which leads to low pav, pp-p and a main frequency amplitude at P1. In addition, the cavity covered the whole suction side under H = 13.6 m and 15.5 m, which led the pp-p and dominant frequency amplitude of pressure fluctuation at P2 and P3 under critical cavitation to be higher than that under normal conditions.

Horizontal Pressure Fluctuation in Bubbling Fluidized Bed

2003 ◽  
Author(s):  
Vesa V. Walle´n
Keyword(s):  
Pressure Gradient ◽  
Fluidized Bed ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
Middle Part ◽  
Biomass Combustion ◽  
Bottom Part ◽  
Pressure Transducers ◽  
Bubbling Fluidized Bed ◽  
Horizontal Pressure

Pressure measurements were conducted in a two-dimensional hot atmospheric bubbling fluidized bed reactor in the laboratory of Energy and Process Engineering at Tampere University of Technology. A set of six fast pressure transducers was used to detect the rapid pressure fluctuations inside the bubbling bed of the reactor. These pressure transducers were placed both vertically and horizontally into the reactor. From these measurements it was found that the vertical pressure fluctuation took place at the same time at different levels of the bed. Also the same fluctuation could be seen under the air distributor. The horizontal pressure fluctuation was found to vary both by place and time. At the bottom part of the bed the highest pressure peaks was found at centre of the bed. Most of the time there was a pressure gradient the highest pressure being in the centre of the bed. This gradient creates horizontal flow of gases from middle to the sides. The velocity of this flow varies with the size of the pressure gradient. The opposite effect can be found in the upper part of the bed. The highest pressure was no more in the middle part of the bed. Instead, it was found to be between the centre of the bed and left and right walls. The pressure was low at the walls but also rather low at the middle of the bed. There must be flow towards the walls and to the centre axis. These pressure fluctuations can provide an explanation for the well-known “wandering plume” effect. They can also give a tool to better describe the mixing inside a bubbling fluidized bed. This kind of tool is needed when biomass combustion is modelled in bubbling fluidized bed.

Pressure Fluctuations and Flow-Induced Vibration Measurements in a Hard Disk Drive under Different Rotation Speeds

2012 ◽  
Vol 197 ◽  
pp. 292-296 ◽  
Author(s):  
He Qun Min ◽  
Xiao Yang Huang ◽  
Qi De Zhang
Keyword(s):  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
Hard Disk Drives ◽  
Experimental Studies ◽  
Laser Doppler Vibrometer ◽  
Hard Disk ◽  
Disk Drive ◽  
Disk Drives ◽  
Flow Induced Vibration ◽  
Causal Nexus

Flow-induced vibration (FIV) of a head gimbals assembly (HGA) in hard disk drives (HDDs) limits the positioning accuracy of magnetic head in the HGA for higher HDD magnetic recording density. The pressure fluctuations characterize turbulent fluctuations exciting the HGA off-track vibration (HGA-OTV). In this paper, experimental studies have been carried out to investigate the spectrum characteristics correspondence between pressure fluctuations around an HGA and the simultaneous HGA-OTV under different HDD rotation speeds. A practical and effective experimental setup has been implemented to enable the simultaneous measurements on both the pressure fluctuation and HGA-OTV signals, where pressure fluctuations are measured with a pressure transducer through a small hole on the HDD top cover and the direct HGA-OTV signals are detected through a laser Doppler vibrometer. Results under conditions of three different HDD rotation speeds of 7200, 9000, 10800 rpm have been investigated and compared. It is shown that the HGA off-track vibration spectra are highly associated with those of the pressure fluctuations in terms of principal peaks in four frequency bands around 1.8 kHz, 2.5-3.5 kHz, 7-7.5 kHz and 11.5-12.5 kHz. With increasing HDD rotation speed, it is shown that the spectrum magnitudes of both the pressure fluctuation and the HGA off-track vibration increase correspondingly, while the principal peak positions in spectra of either pressure fluctuation or the HGA off-track vibration always hold the line. This study demonstrates a causal nexus from the pressure fluctuation to the HGA off-track vibration and suggests the feasibility of controlling the HGA-OTV through suppression of pressure fluctuations around the HGA.

scholarly journals Experimental evidence dynamic pressures reduction on plunge pool floors downstream flip bucket for increasing downstream face slopes

2020 ◽  
Vol 20 (5) ◽  
pp. 1834-1846 ◽  
Author(s):  
Mehdi Karami Moghadam ◽  
Ata Amini ◽  
Hasan Hosseini
Keyword(s):  
Extreme Values ◽  
International Association ◽  
Dynamic Pressure ◽  
Pressure Coefficient ◽  
Pressure Fluctuations ◽  
Laboratory Data ◽  
Bottom Wall ◽  
Downstream Face ◽  
Maximum Value ◽  
Mean Pressure

Abstract In this research, the ejecting jet from a flip bucket downstream of a chute spillway was simulated using physical modeling. The effects of influencing parameters upon fluctuations and extreme values of dynamic pressure were investigated. The angles of 0°, 30°, 45°, and 60° were adopted for the mobile bottom wall. The discharges were set as 67, 86, 161, and 184 litre/s and the depths of water cushion on the mobile bottom wall were set as 0, 15, 30, and 45 cm. The method suggested by Castillo for computation of fluctuating coefficient of dynamic pressure (see Castillo (2007) Pressure characterization of undeveloped and developed jets in shallow and deep pool. Proceedings of the Congress-International Association for Hydraulic Research32 (2), 645) was validated via the laboratory data. The results showed that the increase in water cushion depth downstream has led to a decrease in mean pressure and in pressure fluctuations. The analyses showed that the fluctuating pressure coefficient was a function of water cushion depth, and its maximum value was taken when there was a water cushion on the mobile bottom wall. With an increase in discharge and mobile bottom wall angle, the maximum value of the fluctuating coefficient occurred in less water cushion depth. Moreover, with the growth of discharge, the maximum positive and negative fluctuations of the pressure increased first and then decreased.

scholarly journals TRANSVERSELY STREAMLINED CYLINDER ON RIGID SURFACE

2021 ◽  
pp. 87-94
Author(s):  
V. A. Voskoboinick ◽  
O. A. Voskoboinyk ◽  
A. M. Onishchenko ◽  
A. V. Voskobijnyk
Keyword(s):  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
Experimental Studies ◽  
Separated Flow ◽  
Wall Pressure ◽  
Mathematical Statistics ◽  
Mathematical Apparatus ◽  
Rigid Surface ◽  
Research Results ◽  
Wall Pressure Fluctuations

The results of experimental studies are presented in order to study the features of the formation of separated and vortex flows in the vicinity of a transversely streamlined cylinder on the surface of a hydraulically smooth rigid surface and to determine the space-time characteristics of sources of wall pressure fluctuations. The studies were carried out in laboratory conditions on transversely streamlined cylinders, which were located on a rigid surface. The field of wall pressure fluctuations was measured by a group of miniature piezoceramic pressure fluctuation sensors, which were installed flush with the streamlined rigid surface in front of the cylinder and in its wake. The research results were processed and analyzed using the mathematical apparatus of the theory of probability and mathematical statistics. The spectral and correlation characteristics of the separated flow in the vicinity of a transversely streamlined cylinder are obtained.

Experimental Studies of Sedimentation Basin Dynamics

1977 ◽  
Vol 12 (1) ◽  
pp. 77-90
Author(s):  
J.F. Cordoba-Molina ◽  
P.L. Silveston ◽  
R. R. Hudgins
Keyword(s):  
Dynamic Response ◽  
Froude Number ◽  
Flow Model ◽  
Experimental Studies ◽  
Densimetric Froude Number ◽  
Number Range ◽  
The Real ◽  
Highly Correlated ◽  
Sedimentation Basins ◽  
Simple Flow

Abstract A simple Flow Model is proposed to describe the dynamic response of sedimentation basins. The response predicted by this model is linear as opposed to the real response of the basin which is nonlinear. However, the real response of the basin is highly correlated with its densimetric Froude number, and as a consequence our linear model effectively predicts the response of the basin in a restricted densimetric Froude Number range. Our experiments show that the response of the basin becomes more sluggish and erratic as the densimetric Froude number decreases.

scholarly journals Probability Characteristics, Area Reduction, and Wind Directionality Effects of Extreme Pressure Coefficients of High-Rise Buildings

2021 ◽  
Vol 11 (15) ◽  
pp. 7121
Author(s):  
Shouke Li ◽  
Feipeng Xiao ◽  
Yunfeng Zou ◽  
Shouying Li ◽  
Shucheng Yang ◽  
...  
Keyword(s):  
Probability Distribution ◽  
Pressure Coefficient ◽  
Wind Pressure ◽  
Extreme Pressure ◽  
Distribution Law ◽  
Distribution Fitting ◽  
Pressure Coefficients ◽  
High Rise ◽  
Area Reduction ◽  
The Mean

Wind tunnel tests are carried out for the Commonwealth Advisory Aeronautical Research Council (CAARC) high-rise building with a scale of 1:400 in exposure categories D. The distribution law of extreme pressure coefficients under different conditions is studied. Probability distribution fitting is performed on the measured area-averaged extreme pressure coefficients. The general extreme value (GEV) distribution is preferred for probability distribution fitting of extreme pressure coefficients. From the comparison between the area-averaged coefficients and the value from GB50009-2012, it is indicated that the wind load coefficients from GB50009-2012 may be non-conservative for the CAARC building. The area reduction effect on the extreme wind pressure is smaller than that on the mean wind pressure from the code. The recommended formula of the area reduction factor for the extreme pressure coefficient is proposed in this study. It is found that the mean and the coefficient of variation (COV) for the directionality factors are 0.85 and 0.04, respectively, when the orientation of the building is given. If the uniform distribution is given for the building’s orientation, the mean value of the directionality factors is 0.88, which is close to the directionality factor of 0.90 given in the Chinese specifications.

Experimental Investigation of Pressure Fluctuations on Inner Wall of a Centrifugal Pump

2019 ◽  
Vol 36 (4) ◽  
pp. 401-410 ◽  
Author(s):  
Xiao-Qi Jia ◽  
Bao-Ling Cui ◽  
Zu-Chao Zhu ◽  
Yu-Liang Zhang
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
High Flow ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Flow Rates ◽  
Pressure Distributions ◽  
Blade Passing Frequency

Abstract Affected by rotor–stator interaction and unstable inner flow, asymmetric pressure distributions and pressure fluctuations cannot be avoided in centrifugal pumps. To study the pressure distributions on volute and front casing walls, dynamic pressure tests are carried out on a centrifugal pump. Frequency spectrum analysis of pressure fluctuation is presented based on Fast Fourier transform and steady pressure distribution is obtained based on time-average method. The results show that amplitudes of pressure fluctuation and blade-passing frequency are sensitive to the flow rate. At low flow rates, high-pressure region and large pressure gradients near the volute tongue are observed, and the main factors contributing to the pressure fluctuation are fluctuations in blade-passing frequency and high-frequency fluctuations. By contrast, at high flow rates, fluctuations of rotating-frequency and low frequencies are the main contributors to pressure fluctuation. Moreover, at low flow rates, pressure near volute tongue increases rapidly at first and thereafter increases slowly, whereas at high flow rates, pressure decreases sharply. Asymmetries are observed in the pressure distributions on both volute and front casing walls. With increasing of flow rate, both asymmetries in the pressure distributions and magnitude of the pressure decrease.

EXPERIMENTAL STUDIES ON THE DEVELOPMENT OF AN AUTOMATED SYSTEM FOR REGULATING THE SOIL DENSITY USED IN A SEEDING MACHINE

2021 ◽  
pp. 9-15
Author(s):  
ALEKSEI S. DOROKHOV ◽  
Keyword(s):  
Control System ◽  
Automatic Control ◽  
Automatic Control System ◽  
Power Supply ◽  
Experimental Studies ◽  
Automated System ◽  
Statistical Characteristics ◽  
Vegetable Crops ◽  
Soil Density ◽  
Density Control

Research on the development of an automatic control system for the rolling-in working units is aimed at establishing the reliability and analytical relationships, determining the quality indicators of work in real conditions of the rolling-in working units of a seeding machine, and checking the patterns obtained in the fi eld and identifi ed theoretically. Research on the development of an automatic control system for the rolling implements was carried out when sowing dragee seeds of table beet of the Bordeaux variety with a seeding unit consisting of a Belarus-4235 tractor and a Monopil S15/12 precision seeding machine. The system for automatic control of soil density includes the main hardware and software: actuators for maintaining and deepening the rolling working units, microcontrollers, motor drivers, a non-contact ultrasonic sensor, a power supply unit and a sensor for measuring soil density. The paper presents the results of a study to determine the soil density when sowing seeds of table beet, depending on the moisture content of the soil in the sowing layer. The authors describe research methodology, provide graphical relationships between changes in soil density and the depth of seeding, and comment on the main obtained statistical characteristics of the experiment. As a result of the study, structural, echnological and functional diagrams of a rolling rink with an automatic control system using electronically controlled electric cylinders (linear actuators) have been developed. The optimal parameters of the linear drive of the press roller have been established: power - 50W, power supply - 12V, rod stroke - 200…600 mm, speed - 10…45 mm/s, load - 200…900 N. Experimental studies have shown the applicability of the presented system of the automatic control of soil density, which ensures the optimum density of the seedbed of 1.3…1.4 g/cm³. The described technique can be used to develop a soil density control system when sowing seeds of other vegetable crops.

The Effects of Upstream Flexible Barrier on the Debris Flow Entrainment and Impact Dynamics on a Terminal Barrier

2021 ◽  
Author(s):  
Hervé Vicari ◽  
C.W.W. Ng ◽  
Steinar Nordal ◽  
Vikas Thakur ◽  
W.A. Roanga K. De Silva ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Impact Force ◽  
Dynamic Pressure ◽  
Pressure Coefficient ◽  
Flexible Barrier ◽  
Impact Forces ◽  
Flexible Barriers ◽  
The Impact ◽  
Bed Entrainment

The destructive nature of debris flows is mainly caused by flow bulking from entrainment of an erodible channel bed. To arrest these flows, multiple flexible barriers are commonly installed along the predicted flow path. Despite the importance of an erodible bed, its effects are generally ignored when designing barriers. In this study, three unique experiments were carried out in a 28 m-long flume to investigate the impact of a debris flow on both single and dual flexible barriers installed in a channel with a 6 m-long erodible soil bed. Initial debris volumes of 2.5 m<sup>3</sup> and 6 m<sup>3</sup> were modelled. For the test setting adopted, a small upstream flexible barrier before the erodible bed separates the flow into several surges via overflow. The smaller surges reduce bed entrainment by 70% and impact force on the terminal barrier by 94% compared to the case without an upstream flexible barrier. However, debris overflowing the deformed flexible upstream barrier induces a centrifugal force that results in a dynamic pressure coefficient that is up to 2.2 times higher than those recommended in guidelines. This suggests that although compact upstream flexible barriers can be effective for controlling bed entrainment, they should be carefully designed to withstand higher impact forces.

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