Analysis of effects of air pocket on hydraulic failure of urban drainage infrastructure

2004 ◽  
Vol 31 (1) ◽  
pp. 86-94 ◽  
Author(s):  
F Zhou ◽  
F Hicks ◽  
P Steffler
Keyword(s):  
Air Flow ◽  
Urban Drainage ◽  
Storm Events ◽  
Pressure Oscillations ◽  
Trapped Air ◽  
Hydraulic Failure ◽  
Air Pocket ◽  
Flow Oscillations ◽  
Entrapped Air ◽  
Peak Pressures

The effects of trapped air on flow oscillations and pressure surges in a model trunk sewer–manhole system subject to rapid filling are investigated. The study reveals the detrimental impacts of entrapped air during severe storm events under which pipelines are likely overloaded. The results of the investigation indicated huge peak pressures and severe pressure oscillations inside the system.Key words: trapped air, flow transient, rapid filling, sewers.

Computation of the Unstable Behavior of a Hydraulic Circuit With a Centrifugal Pump Coupled to an Air Pocket

2005 ◽  
Author(s):  
Jorge Parrondo ◽  
Juan Antun˜a ◽  
Jose´ I. Prieto
Keyword(s):  
Centrifugal Pump ◽  
Compressible Liquid ◽  
Hydraulic Systems ◽  
Calculation Algorithm ◽  
Trapped Air ◽  
Air Pocket ◽  
Dead End ◽  
Entrapped Air ◽  
The One ◽  
Oscillation Instability

A theoretical and experimental study is presented on the mass oscillation instability in hydraulic systems with entrapped gas pockets and pumps with positive slope in the head curve. In order to simulate these systems, the one-dimensional unsteady equations for compressible liquid flow were solved by means of a suitable calculation algorithm, based on the method of characteristics. Additionally, a series of laboratory tests was conducted on a conventional centrifugal pump that operated in a circuit with a dead end and different amounts of entrapped air. In accordance with the predictions of the theoretical model, instability was found to develop with limit cycle pressure oscillations of frequency dependent on the trapped air amount.

scholarly journals Assessment of Steady and Unsteady Friction Models in the Draining Processes of Hydraulic Installations

Water ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 1888
Author(s):  
Óscar E. Coronado-Hernández ◽  
Ivan Derpich ◽  
Vicente S. Fuertes-Miquel ◽  
Jairo R. Coronado-Hernández ◽  
Gustavo Gatica
Keyword(s):  
Mathematical Model ◽  
Turbulent Flow ◽  
Water Velocity ◽  
Experimental Facility ◽  
Governing Equations ◽  
Pressure Oscillations ◽  
Air Pocket ◽  
Friction Models ◽  
The Mathematical Model

The study of draining processes without admitting air has been conducted using only steady friction formulations in the implementation of governing equations. However, this hydraulic event involves transitions from laminar to turbulent flow, and vice versa, because of the changes in water velocity. In this sense, this research improves the current mathematical model considering unsteady friction models. An experimental facility composed by a 4.36 m long methacrylate pipe was configured, and measurements of air pocket pressure oscillations were recorded. The mathematical model was performed using steady and unsteady friction models. Comparisons between measured and computed air pocket pressure patterns indicated that unsteady friction models slightly improve the results compared to steady friction models.

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.

scholarly journals Development of flood probability charts for urban drainage network in coastal areas through a simplified joint assessment approach

2011 ◽  
Vol 15 (10) ◽  
pp. 3115-3122 ◽  
Author(s):  
R. Archetti ◽  
A. Bolognesi ◽  
A. Casadio ◽  
M. Maglionico
Keyword(s):  
Sea Level ◽  
Drainage System ◽  
Coastal Areas ◽  
Operating Conditions ◽  
Threshold Condition ◽  
Urban Drainage ◽  
Climate Variables ◽  
Storm Events ◽  
Hydraulic Simulation ◽  
Sea Levels

Abstract. The operating conditions of urban drainage networks during storm events depend on the hydraulic conveying capacity of conduits and also on downstream boundary conditions. This is particularly true in coastal areas where the level of the receiving water body is directly or indirectly affected by tidal or wave effects. In such cases, not just different rainfall conditions (varying intensity and duration), but also different sea-levels and their effects on the network operation should be considered. This paper aims to study the behaviour of a seaside town storm sewer network, estimating the threshold condition for flooding and proposing a simplified method to assess the urban flooding severity as a function of climate variables. The case study is a portion of the drainage system of Rimini (Italy), implemented and numerically modelled by means of InfoWorks CS code. The hydraulic simulation of the sewerage system identified the percentage of nodes of the drainage system where flooding is expected to occur. Combining these percentages with both climate variables' values has lead to the definition of charts representing the combined degree of risk "rainfall-sea level" for the drainage system under investigation. A final comparison between such charts and the results obtained from a one-year rainfall-sea level time series has demonstrated the reliability of the analysis.

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.

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.

A Study on the Unstable Coupling Between Pumps and Hydraulic Circuits With Entrapped Gas Pockets

2002 ◽  
Author(s):  
Jorge L. Parrondo-Gayo ◽  
Juan Antun˜a-Schu¨tze ◽  
Jose´ Gonza´lez-Pe´rez ◽  
Joaqui´n Ferna´ndez-Francos
Keyword(s):  
Critical Conditions ◽  
Pressure Amplitude ◽  
Hydraulic Systems ◽  
Positive Slope ◽  
One Dimensional ◽  
Numerical Resolution ◽  
Air Pocket ◽  
Entrapped Air ◽  
Fundamental Equations ◽  
Oscillation Instability

A theoretical and experimental study has been conducted on the mass oscillation instability in hydraulic systems with entrapped gas pockets and pumps with positive slope in the head curve. The theoretical study was composed of an analysis of the critical conditions for the instability to develop, followed by the numerical resolution of the fundamental equations that govern the phenomenon, assuming unsteady one-dimensional flow, in order to simulate the limit cycle oscillations of the unstable system. Additionally a series of laboratory tests was conducted on a conventional centrifugal pump, with variation of the initial volume of an entrapped air pocket in the circuit. As expected from the predictions of the theoretical model, instability was found to developed with pressure amplitude oscillations and frequency dependent on the amount of entrapped air.

Deriving discharge strategies to reduce CSO in urban drainage systems

1997 ◽  
Vol 36 (8-9) ◽  
pp. 259-263
Author(s):  
K.-J. Breur ◽  
P. E. R. M. van Leeuwen ◽  
N. P. Dellaert
Keyword(s):  
System Performance ◽  
Major Part ◽  
Design Procedure ◽  
Urban Drainage ◽  
Specific Situation ◽  
Storm Events ◽  
Maximum Reduction ◽  
Actual Design ◽  
Heavy Storm

This paper discusses the design of discharge strategies for urban drainage operation. The design procedure applies a tuneable strategy which can be adjusted to a specific situation by adjusting a few parameters which reflect the discharge priority of the various districts of the system. The actual design procedure, a procedure of simulation and analysis of the system performance, is explained in a case study. Apart form the method, the case study shows that a near optimal performance (maximum reduction of overflow volume) can be realised by applying an “event” average strategy (one strategy for all type of inflow events). Furthermore, the case study shows that the major part of the total overflow volume is caused by very heavy storm events.

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