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.

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 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.

Effects of water–air mixtures on hydraulic transients

2010 ◽  
Vol 37 (9) ◽  
pp. 1189-1200 ◽  
Author(s):  
Oscar Pozos ◽  
Alejandro Sanchez ◽  
Eduardo A. Rodal ◽  
Yuri V. Fairuzov
Keyword(s):  
Bubbly Flow ◽  
Experimental Investigations ◽  
Hydraulic Transients ◽  
Two Phase ◽  
Pressure Transients ◽  
Air Content ◽  
Air Pocket ◽  
Pressurized Pipelines ◽  
Air Pockets ◽  
The Impact

The purpose of this study is to investigate pressurized pipelines and the potential effects on pressure transients of air entrained at the downstream end of large entrapped air pockets followed by a hydraulic jump in pressurized pipelines. The homogeneous two-phase flow model is used to simulate the transient response of the bubbly mixture after a pump shutdown. The results show that pressure transients are significantly reduced with increasing air-pocket volumes and bubbly flow air content. Experimental investigations were carried out to analyze the impact of different air-pocket volumes located at high points of pressurized pipelines. A case study of an existing pumping system was considered to exemplify the impact of the bubbly flow air content on hydraulic transients.

scholarly journals Numerical Study on the Commissioning Charge-Up Process of Horizontal Pipeline with Entrapped Air Pockets

2014 ◽  
Vol 6 ◽  
pp. 838926 ◽  
Author(s):  
Xinyu Zhang ◽  
Bo Yu ◽  
Yan Wang ◽  
Jianyu Xie ◽  
Dongping Qiu ◽  
...  
Keyword(s):  
Process Design ◽  
Pressure Field ◽  
Numerical Study ◽  
Critical Parameters ◽  
Hydraulic Characteristics ◽  
Oil Pipeline ◽  
Air Pocket ◽  
Acute Change ◽  
Entrapped Air ◽  
Air Pockets

Accurately predicting hydraulic characteristics in the charge-up process of horizontal pipeline with entrapped air pocket is of great significance for the process design and field operation of the oil pipeline commissioning. In this paper, this process is simulated and its hydraulic characteristics are analyzed. Finite difference method and characteristic method are combined to obtain the velocity and pressure field of the whole line. Results show that when air pockets reach the outlet of the pipeline, they blow out tempestuously and the velocity of gas may reach tens times of its normal flow velocity. At the beginning and end of the blowing out, velocity and pressure of the whole line suffer acute change. Based on this, the influence of several critical parameters is compared and analyzed by several groups of examples.

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.

Effects of stator splitter blades on aerodynamic performance of a single-stage transonic axial compressor

2020 ◽  
Vol 14 (4) ◽  
pp. 7369-7378
Author(s):  
Ky-Quang Pham ◽  
Xuan-Truong Le ◽  
Cong-Truong Dinh
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Aerodynamic Performance ◽  
Numerical Results ◽  
Single Stage ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Operating Stability ◽  
Length Coverage

Splitter blades located between stator blades in a single-stage axial compressor were proposed and investigated in this work to find their effects on aerodynamic performance and operating stability. Aerodynamic performance of the compressor was evaluated using three-dimensional Reynolds-averaged Navier-Stokes equations using the k-e turbulence model with a scalable wall function. The numerical results for the typical performance parameters without stator splitter blades were validated in comparison with experimental data. The numerical results of a parametric study using four geometric parameters (chord length, coverage angle, height and position) of the stator splitter blades showed that the operational stability of the single-stage axial compressor enhances remarkably using the stator splitter blades. The splitters were effective in suppressing flow separation in the stator domain of the compressor at near-stall condition which affects considerably the aerodynamic performance of the compressor.

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