scholarly journals Modulation of transient pressure by an air pocket in a horizontal pipe with an end orifice

2018 ◽  
Vol 77 (10) ◽  
pp. 2528-2536 ◽  
Author(s):  
Lin Li ◽  
David Z. Zhu
Keyword(s):  
Open Channel ◽  
Peak Pressure ◽  
Water Hammer ◽  
Sudden Increase ◽  
Transient Pressure ◽  
Horizontal Pipe ◽  
Air Pocket ◽  
Large Orifice ◽  
Air Pockets ◽  
End Wall

Abstract In urban drainage systems, a sudden increase in the flow rate can cause the transition of the flow from open channel to pipe flow, and the entrapment of large air pockets in sewers, which might result in serious geysers and water-hammer like pressure events. This paper presents a numerical analysis of flow processes associated with the pressurization and release of an air pocket in order to study its influence on transient pressure in a horizontal pipe with an end orifice. The influence of the air pocket inside the pipe on the peak pressure can be described in two distinct regimes. In regime I for the pipe with a small orifice, the peak pressure is modulated by the pressurization and expansion of the air pocket and its subsequent damping. In regime II for the pipe with a large orifice, air can be quickly expelled, and the water column directly impinges on the pipe end wall and causes water-hammer like pressure. With the increase of the orifice size, the peak pressure decreases due to the change in the water velocity. In the study cases, the peak pressure in regime I is about two times the inlet pressure, while it can be more than forty times in regime II.

scholarly journals Impact pressure on an orifice plate by a rising water column driven by an air pocket in a vertical riser

2020 ◽  
Vol 81 (5) ◽  
pp. 1029-1038 ◽  
Author(s):  
Yu Qian ◽  
David Z. Zhu
Keyword(s):  
Water Column ◽  
Peak Pressure ◽  
Current Model ◽  
Strong Relationship ◽  
Water Hammer ◽  
Orifice Plate ◽  
Minor Effect ◽  
Initial Water ◽  
Air Pocket ◽  
Riser Height

Abstract Occurrences of storm geyser events have attracted significant attention in recent years. Previous studies suggest that using an orifice plate can reduce the intensity of a geyser event but may induce a water-hammer type of pressure on the orifice plate. This study was conducted to explore the factors that influence the pressure transients when an orifice plate was installed in a vertical riser. A novel model was developed to simulated the movement of a rising water column driven by an air pocket in a vertical riser with an orifice plate on the top. Water-hammer type of pressure occurs when the water column reaches the orifice plate. The current model accurately simulates the dynamics of the water column considering its mass loss due to the flow along the wall of the riser (film flow) and the existence of the orifice plate. It was found that the initial water column length and the driving pressure, as well as the riser material, have a strong relationship with the peak pressure. The riser diameter and riser height have minor effect on the peak pressure. The water-hammer induced peak pressure reaches the maximum when the orifice opening is around 0.2 times the diameter of the vertical riser.

scholarly journals Development of Pant-Type Harness with Fabric Air-Pocket for Pain Relief

2019 ◽  
Vol 9 (9) ◽  
pp. 1921
Author(s):  
Dongwoo Nam ◽  
Miyeon Kwon ◽  
Juhea Kim ◽  
Bummo Ahn
Keyword(s):  
Contact Area ◽  
Peak Pressure ◽  
Applied Pressure ◽  
The Body ◽  
Area Measurement ◽  
Medical Applications ◽  
Air Pocket ◽  
Long Time ◽  
Developed Pressure ◽  
Air Pockets

Harnesses can be used in various applications, such as entertainment, rescue operations, and medical applications. Because users are supported on the harness for a long time, they should feel comfortable wearing the harnesses. However, existing commercial harnesses are uncomfortable to wear and cause continuous serious pain. Therefore, in this study, a new pant-type harness with a fabric air pocket to reduce the applied pressure on the body, especially in the groin, is proposed. Keeping this in mind, we have designed and developed the pant-type harness. In addition, we performed pressure and contact area measurement experiments using the harness developed, pressure sensor, and a human mannequin. Peak and mean pressures and contact areas near the groin and waist were measured in the experiments. From the results, when air is injected in the air pockets, the peak pressure and contact area near the waist increased, and the peak pressure near the groin decreased. This means that the pressure applied on the human mannequin near the groin reduces because of the increased contact area near the waist, which is achieved by multi-layered air pockets. In this study, we proposed the optimal design of a novel pant-type harness that can address the limitations of existing harnesses. The proposed harness can be used for a prolonged time in applications, such as virtual reality entertainment, rescue operations, and rehabilitation.

On the Hydraulics of Downward Sloping Pipes With Entrapped Air Pockets

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
H. A. Warda ◽  
E. M. Wahba ◽  
E. N. Ahmed
Keyword(s):  
Hydraulic Jump ◽  
Open Channel ◽  
Numerical Results ◽  
Navier Stokes ◽  
Experimental Investigations ◽  
Dynamics Model ◽  
Computational Fluid Dynamics Model ◽  
Air Pocket ◽  
Entrapped Air ◽  
Air Pockets

Abstract In this study, air–water flow in a downward sloping pipe subsequent to the entrapping of an air pocket is investigated both numerically and experimentally. A transient, two-dimensional computational fluid dynamics model is applied to study the different possible flow regimes and their associated phenomena. The numerical model is based on the Reynolds-averaged Navier–Stokes (RANS) equations and the volume of fluid (VOF) method. Both numerical and experimental investigations provide visualization for the hydraulic jump, the blowback regime, and the full gas transport regime. The numerical results predict that the flow structure in the pipe downstream the toe of the hydraulic jump is subdivided into three distinct regions including the jet layer, the shear zone, and the circulation region, which agrees qualitatively with the previous investigations of the hydraulic jump characteristics in open channel flow. Numerical results are in reasonable agreement with the experimental measurements of the circulation length and the hydraulic jump head loss.

scholarly journals Numerical modelling of pipelines with air pockets and air valves

2016 ◽  
Vol 43 (12) ◽  
pp. 1052-1061 ◽  
Author(s):  
Vicente S. Fuertes-Miquel ◽  
P. Amparo López-Jiménez ◽  
F. Javier Martínez-Solano ◽  
Gonzalo López-Patiño
Keyword(s):  
Numerical Modelling ◽  
Water Column ◽  
Water Hammer ◽  
Extreme Conditions ◽  
Residual Velocity ◽  
Air Pocket ◽  
Air Valve ◽  
Air Pockets

This work considers the behaviour of air inside pipes when the air is expelled through air valves. Generally, the air shows isothermal behaviour. Nevertheless, when the transient is very fast, it shows adiabatic behaviour. In a real installation, an intermediate evolution between these two extreme conditions occurs. Thus, it is verified that the results vary significantly depending on the hypothesis adopted. To determine the pressure of the air pocket, the most unfavourable hypothesis (isothermal behaviour) is typically adopted. Nevertheless, from the perspective of the water hammer that takes place when the water column arrives at the air valve and abruptly closes, the most unfavourable hypothesis is the opposite (adiabatic behaviour). In this case, the residual velocity with which the water arrives at the air valve is higher, and, consequently, the water hammer generated is greater.

Experimental Validation of Existing Numerical Models for the Interaction of Fluid Transients With In-Line Air Pockets

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Jane Alexander ◽  
Pedro J. Lee ◽  
Mark Davidson ◽  
Huan-Feng Duan ◽  
Zhao Li ◽  
...  
Keyword(s):  
Time Delay ◽  
Wave Speed ◽  
Numerical Models ◽  
Diagnostic Process ◽  
Air Pocket ◽  
Fluid Transients ◽  
Entrapped Air ◽  
Air Pockets ◽  
The Given ◽  
Potential Tool

Entrapped air in pipeline systems can compromise the operation of the system by blocking flow and raising pumping costs. Fluid transients are a potential tool for characterizing entrapped air pockets, and a numerical model which is able to accurately predict transient pressures for a given air volume represents an asset to the diagnostic process. This paper presents a detailed study on our current capability for modeling and predicting the dynamics of an inline air pocket, and is one of a series of articles within a broader context on air pocket dynamics. This paper presents an assessment of the accuracy of the variable wave speed and accumulator models for modeling air pockets. The variable wave speed model was found to be unstable for the given conditions, while the accumulator model is affected by amplitude and time-delay errors. The time-delay error could be partially overcome by combining the two models.

scholarly journals Water Hammer Control Analysis of an Intelligent Surge Tank with Spring Self-Adaptive Auxiliary Control System

Energies ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2527 ◽  
Author(s):  
Wuyi Wan ◽  
Boran Zhang ◽  
Xiaoyi Chen ◽  
Jijian Lian
Keyword(s):  
Control Function ◽  
Water Hammer ◽  
Control Device ◽  
Control Analysis ◽  
Surge Tank ◽  
Transient Pressure ◽  
Supply Pipe ◽  
Proposed Model ◽  
Vertical Size ◽  
Self Adaptive

The water hammer can cause great risks in water supply pipe systems. A surge tank is a kind of general water hammer control device. In order to improve the behavior of the surge tank, a self-adaptive auxiliary control (SAC) system was proposed in this paper. The system can optimize the response of the surge tank according to the transient pressure. The numerical model and the matched boundary conditions were established to simulate the improved surge tank and optimize the SAC system. Then, various transient responses were simulated by the proposed model with different parameters set. The proposed system is validated by comparing the water hammer process in a river-pipe-valve (RLV) system with and without SAC. The results show that the SAC can greatly improve the water hammer control of the pipeline and the water level oscillation of the surge tank. With the SAC system, the required vertical size of the surge tank can be significantly reduced with the desired water hammer control function.

Large Scale Experimental Wave Impact on Walls in the Québec Coastal Physics Laboratory

2015 ◽  
Author(s):  
Jannette B. Frandsen ◽  
Francis Bérubé
Keyword(s):  
Large Scale ◽  
Peak Pressure ◽  
Vertical Wall ◽  
Test Series ◽  
Vertical Force ◽  
Wave Impact ◽  
Physics Laboratory ◽  
Air Pocket ◽  
Jet Velocity ◽  
Plunging Breaker

The present tests are conducted in the new Québec Coastal Physics Laboratory, Canada. The flume has a depth and a width of 5 m and is 120 m long. This paper presents large scale experiments of water wave impact on a vertical wall following wave runup on a mixed sand-gravel-cobble beach. This present study is concerned with advancing knowledge on rapidly varying pressure magnitude and distributions on different types of sea/river/harbor walls. Protection against extreme events and subsequent coastal erosion is a key theme of application. Herein is presented preliminary test series which has focus on forces on vertical walls. Specifically, 27 pressure sensors are mounted on the vertical wall with a total test area of 1.2 m wide and 2.4 m high and is a stiffened aluminum plate. The outer regions of the wall are made of steel to span the entire width of the tank. The wall is designed to behave as a rigid plate. The geometric model to full scale is about 1:4. The incoming waves evolve on a flat bed to climb the final 25 m on a beach with slope with constant slope of 1:10. A small regular wave train forms the basis for investigations of force patterns on the wall. Herein, our preliminary findings reported are based on selected 6 test series (18 impacts out of 150 impacts). In general, wall pressures greater than 1 MPa and 10 m run-up are easily developed even with moderate amplitude waves at the inlet. We will discuss some details of the underlying mechanism of various types of breaking and impact on the wall. The peak pressure identified on the wall with the mixed gravel beach surface was 1.23 million N/m2 occurring in 0.2 milli seconds. It was cuased by a plunging breaker with a relatively large air pocket (∼0.11 m2). It was further identified that the maximum pressure on the wall does not necessarily give the maximum jet velocity (equivalent to vertical force considered in design of on parapets). They are independent quantities in these very random rapid processes. The maximum jet velocity was in the order of 35 m/s but could higher on a different beach surface. Further, it was found that the maximum waves are not necessarily the most critical ones as the waves break and therefore dissipates its energy before reaching the wall. A plunging breaker with a relatively large airpocket with a crest tip located at the top part of the wall resulted in max. peak wall pressure. One impact case caused a near simultaneous double peak pressure generated by a plunging breaker with two relatively small airpockets (0.003 m2 and 0.01 m2). This was the impact case responsible for the max. vertical jet velocity. We further found that the max. peak water pressure of the plunging breakers had a similar order of magnitude as the max. pressure within an air pocket.

Transient Pressure Analysis of a Prototype Pump Turbine: Field Tests and Simulation

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Jinhong Hu ◽  
Jiandong Yang ◽  
Wei Zeng ◽  
Jiebin Yang
Keyword(s):  
Field Tests ◽  
Water Hammer ◽  
Hydropower Plant ◽  
Pressure Pulsations ◽  
Transient Pressure ◽  
Pump Turbine ◽  
Operation Conditions ◽  
Spiral Case ◽  
Transient Events ◽  
Transient Variations

The transient behaviors of a prototype pump turbine are very important to the safe operation of a pumped-storage power plant. This is because the water hammer pressure during transient events affects the pressure surges in the spiral case (SC) and the draft tube (DT). In addition, the transient pressure pulsations in the vaneless space (VL) are important in the evaluation of the life of the runner. Although several detailed studies have been conducted on the water hammer pressure of a hydropower plant, very few have considered the transient pressure pulsations that occur in the pump turbine. The objective of the present study was to determine the characteristics of the transient pressure pulsations of a 300-MW prototype Francis pump turbine during load rejection and power failure. For this purpose, the frequency features in the steady-state were first analyzed using fast Fourier transform. A Savitzky–Golay filter was then used to extract the water hammer pressure and pulsating pressure from the acquired raw pressure signals. Further, a one-dimensional (1D) method of characteristics (MOC) mathematical model of the pump-turbine was established and used to simulate the transient variations of the flow discharge during transient events, to enable the division of the transient operation conditions into several domains. Finally, the characteristics of the transient pressure pulsations in the SC, vaneless space, and DT were investigated in the time and frequency domains. This paper also discusses the causes of the pressure pulsations that occur under different modes of operation of a pump turbine.

scholarly journals Investigation of the combined effect of air pockets and air bubbles on fluid transients

2017 ◽  
Vol 20 (2) ◽  
pp. 376-392 ◽  
Author(s):  
Oscar Pozos-Estrada
Keyword(s):  
Bubbly Flow ◽  
Combined Effect ◽  
Hyperbolic Partial Differential Equations ◽  
Experimental Investigations ◽  
Air Bubbles ◽  
Two Phase ◽  
Pressure Transients ◽  
Air Pocket ◽  
Experimental Apparatus ◽  
Air Pockets

Abstract This paper presents numerical and experimental investigations of the combined effect on pressure transients of air pockets and homogenous water–air bubble mixtures. An air pocket can accumulate at a high point of a pipeline along the control section located at the transition between pipes with sub- and supercritical slope, forcing open channel flow conditions underneath the pocket that ends in a hydraulic jump at the downward sloping pipe. The turbulence action at the jump generates small air bubbles that are entrained and transported along the pipe producing a two-component bubbly flow within the continuous liquid phase. A numerical model is developed, combining the explicit–implicit scheme proposed by McGuire and Morris and the method of characteristics for solving the quasi-linear hyperbolic partial differential equations for transient two-phase flow expressed in conservation form. To verify the proposed model, an experimental apparatus made of PVC was used to carry out hydraulic transient experiments. Tests were conducted in a tank–pipe–valve system and a valve with a pneumatic actuator at the downstream end generated transients. Numerical results at the test section pipe compares favorably with experimental data. The results show that pressure transients are significantly reduced with increasing air-pocket volumes and bubbly flow air content.

Water Hammer Characteristics of Glass Reinforced Plastic Oil Transportation Pipeline

2011 ◽  
Vol 204-210 ◽  
pp. 127-130 ◽  
Author(s):  
Chang Jun Li ◽  
Xia Wu ◽  
Wen Long Jia ◽  
Ke Xi Liao
Keyword(s):  
Pressure Fluctuation ◽  
Peak Pressure ◽  
Mathematic Model ◽  
Water Hammer ◽  
Steel Pipeline ◽  
Oil Transportation ◽  
Reinforced Plastic ◽  
Fluctuation Frequency ◽  
Simulation Results ◽  
Safety Operation

Glass reinforced plastic (GRP) pipeline has good characteristics of anti-corrosion, anti-scaling and it is widely used in the oil transportation pipeline. Analyze the water hammer characteristics of GRP pipeline is essential to ensure the safety operation of the pipeline. The water hammer mathematic model for GRP pipeline is built through combing the general water hammer mathematic model and prosperities of GRP pipeline. The solving method of the model is discussed based on the method of characteristic. Ultimately, the simulation results show the GRP pipeline can reduce the peak pressure and pressure fluctuation frequency as well as increase the low pressure caused by water hammer compared with steel pipeline. The GRP pipeline has a better capability to reduce the harms brought by water hammer than steel pipeline.

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