Blockage

This paper presents the problem of modeling and simulating of transient phenomena in conveying pipeline systems based on the rigid column and full elastic methods. Transient analysis is important and one of the more challenging and complicated flow problem in the design and the operation of water pipeline systems. Transient can produce large pressure forces and rapid fluid acceleration into a water pipeline system, these disturbances may result in device failures, system fatigue or pipe ruptures, and even the dirty water intrusion. Several methods have been introduced and used to analyze transient flow, an accurate analysis and suitable protection devices should be used to protect water pipeline systems. The fourth-order Runge-Kutta method has been used to solve the dynamic and continuity equations in the rigid column method, while the characteristics method used to solve these equations in the full elastic method. The results obtained provide that the model is an efficient tool for...

Most of today’s water supply systems are based on plastic pipes. They are characterized by the retarded strain (RS) that takes place in the walls of these pipes. The occurrence of RS increases energy losses and leads to a different form of the basic equations describing the transient pipe flow. In this paper, the RS is calculated with the use of convolution integral of the local derivative of pressure and creep function that describes the viscoelastic behavior of the pipe-wall material. The main equations of a discrete bubble cavity model (DBCM) are based on a momentum equation of two-phase vaporous cavitating flow and continuity equations written initially separately for the gas and liquid phase. In transient flows, another important source of pressure damping is skin friction. Accordingly, the wall shear stress model also required necessary modifications. The final partial derivative set of equations was solved with the use of the method of characteristics (MOC), which transforms ...

It is well known that the water hammer phenomenon can lead to pipeline system failures. For this reason, there is an increased need for simulation of hydraulic transients. High-density polyethylene (HDPE) pipes are commonly used in various pressurised pipeline systems. Most studies have only focused on water hammer events in a single pipe. However, typical fluid distribution networks are composed of serially connected pipes with various inner diameters. The present paper aims to investigate the influence of sudden cross-section changes in an HDPE pipeline system on pressure oscillations during the water hammer phenomenon. Numerical and experimental studies have been conducted. In order to include the viscoelastic behaviour of the HDPE pipe wall, the generalised Kelvin–Voigt model was introduced into the continuity equation. Transient equations were numerically solved using the explicit MacCormack method. A numerical model that involves assigning two values of flow velocity to the co...

This paper studies the Reynolds number dependence on the effect of axial stress on unsteady pipeline flow. The unsteadiness is caused by sudden and gradual closure of the valve situated at the downstream end of the pipe. The effect generated by the unsteadiness is controlled by varying the Reynolds number (Re). Measurements were taken at different part of the pipe for a full and half closure of the valve at various Reynolds numbers. The pressure head obtained increase as Reynolds number (Re) increases, measurement clearly shows that Reynolds number majorly control the response of the pressure head although other factors like pipe geometry and wave speed which is a function of material properties and working fluid also contribute. Reynolds number control the magnitude but the wavelength of oscillation is unaltered. For all values of Reynolds numbers considered in this study (3750, 4125, 4750, 5250, 6000) with Polyvinyl Chloride (PVC) material used as pipe, its variation caused pressu...

The aim of this paper is to numerically investigate Vibration-Based Leak Detection (VBLD) method in pipeline systems based on Fluid–Structure Interaction (FSI) analysis to predict leakages. In previous investigations, laboratory tests were widely used to study the VBLD technique in small-diameter water loop system pipes. The current project uses Ansys Workbench to extend these findings by integrating Computational Fluid Dynamics (CFD) with Finite Element Analysis (FEA). The study outlines a numerical method for VBLD to identify leakages in a 90-degree pipe elbow by predicting variations in vibration signals, with applications in the oil and gas industry. Firstly, changes in fluid behaviour (centrifugal force, pressure drop, secondary flow, and frictional force) experienced in the internal pipe wall resulting from a probable leakage (modelled as an additional outlet) are determined using CFD. Subsequently, the CFD results are coupled with FEA to model structural responses of the pipe...

The aim of this paper is to numerically investigate Vibration-Based Leak Detection (VBLD) method in pipeline systems based on Fluid–Structure Interaction (FSI) analysis to predict leakages. In previous investigations, laboratory tests were widely used to study the VBLD technique in small-diameter water loop system pipes. The current project uses Ansys Workbench to extend these findings by integrating Computational Fluid Dynamics (CFD) with Finite Element Analysis (FEA). The study outlines a numerical method for VBLD to identify leakages in a 90-degree pipe elbow by predicting variations in vibration signals, with applications in the oil and gas industry. Firstly, changes in fluid behaviour (centrifugal force, pressure drop, secondary flow, and frictional force) experienced in the internal pipe wall resulting from a probable leakage (modelled as an additional outlet) are determined using CFD. Subsequently, the CFD results are coupled with FEA to model structural responses of the pipe...

The installed variable pitch fan (VPF) reverse thrust flow field is obtained from the flow solution of an integrated airframe-engine research model for the complete reverser engagement regime during the aircraft landing run from 140 knots to 40 knots. The model includes a twin-engine airframe, complete flow path representation of a future 40 000 lbf high bypass ratio geared turbofan engine, and a bespoke reverse flow-capable VPF design. The reverse thrust flow field, at all speeds, indicates that the reverse flow out of the nacelle inlet is washed downstream by the freestream toward the engine exit regions. Consequently, reverse flow enters the engine through the bypass nozzle from a 180 deg turn of the washed-down stream. This results in a region of circumferentially varying separated flow at the nozzle lip that acts as a blockage to the reverse flow entry into the engine. To mitigate the blockage issue, smooth guidance of the reverse flow into the engine to avoid separation can be...

Abstract. Sudden closure of a control valve or stopping of a pump, either planned or accidental, produces excess pressure in a fluid-filled pipeline known as water hammer. Water hammer, or hydraulic transient, refers to pressure fluctuations caused by a sudden increase or decrease in flow velocity. Pressure waves in the fluid interact with axial, bending, shear a torsional stress waves in the pipe wall. The interaction between axial stress waves and fluid pressure takes place via the radial expansion and contraction of the pipe wall. It is essential to determine the magnitude and frequency of pressures and forces triggered due to these transients to estimate the stresses and vibration levels in the pipeline. This unsteady state phenomenon deals with the change between kinetic energy and pressure energy. If the pressure induced exceeds the pressure rating of a pipe given by the manufacturer, the pipe may rupture. Detrimental consequence may result unless a pressure protection device ...

Pipe vibration induced by water hammer frequently emerges in water conveyance system, especially in the hydropower plant or pumped storage power station with long diversion pipelines. This vibration in turn affects the hydraulic pulsation so that undesired fluid-structure interaction (FSI) arises. In this research, attention is given to a pipeline embedded in concrete. A six-equation model was derived to describe the fluid-pipe-concrete interaction considering Poisson coupling and junction coupling. With the elastic and homogeneous hypotheses, an iterative approach was proposed to solve this model, and the results were validated by experiment and classical water-hammer theory. Then dynamic FSI responses to water hammer were studied in a reservoir-pipe-valve physical system. Hydraulic pressure, pipe wall stress and axial motion were discussed with respect to different parameters of concrete. Results obtained by the two-equation model, four-equation model and six-equation model show c...

Cálculo de la velocidad de onda para el análisis del golpe de ariete Fecha de entrega: 13 de mayo 2016 Fecha de aceptación: 7 de noviembre 2016 In order to accurately solve the water hammer problem using the Method of the Characteristics MOC is necessary to fulfil with the so−called Courant condition which establishes mandatorily that C n = f(a) = 1 in each pipeline of the system, where a is the wave speed. The value of C n is dependant of a whose value depends in turn on the fluid properties (density, bulk modulus) and physical characteristics of each pipeline (elasticity modulus, diameter, wall thickness, supporting condition). Because water distribution systems usually has many different pipes, and therefore, many different wave speeds, it can be said that fulfil with C n = 1 in each pipeline is a very difficult task, more when the solution by MOC needs a common time step Δt for all pipe sections of the system. A way of solution to this problem is applying the method of the wave−...

An experiment featuring waterhammer in viscoelastic pipes is presented in which the effects of pipe-wall viscoelasticity on waterhammer pressures are investigated. A large-scale pipeline apparatus made of polyvinyl chloride (PVC) at Deltares, Delft, The Netherlands, has been used to carry out waterhammer experiments. Tests have been conducted in a reservoir-pipeline-valve system consisting of a main viscoelastic pipeline and two short steel pipes placed upstream and downstream of the main pipe. Rapid closure of a manually operated valve at the downstream end generates waterhammer. Repeated measurements at several positions along the pipeline have been recorded; these are plotted in figures and appropriately interpreted.

It is well known that the water hammer phenomenon can lead to pipeline system failures. For this reason, there is an increased need for simulation of hydraulic transients. High-density polyethylene (HDPE) pipes are commonly used in various pressurised pipeline systems. Most studies have only focused on water hammer events in a single pipe. However, typical fluid distribution networks are composed of serially connected pipes with various inner diameters. The present paper aims to investigate the influence of sudden cross-section changes in an HDPE pipeline system on pressure oscillations during the water hammer phenomenon. Numerical and experimental studies have been conducted. In order to include the viscoelastic behaviour of the HDPE pipe wall, the generalised Kelvin–Voigt model was introduced into the continuity equation. Transient equations were numerically solved using the explicit MacCormack method. A numerical model that involves assigning two values of flow velocity to the co...

The closing valve law is a mathemati- cal function that describes the speed variation of the fluid as it is closing. This reduction of the speed de- termines the shape of the pressure wave during the development of the water-hammer. A wide variety of closing modes exists, depending on the valve type and their operation, each one is mathematically giv- en by a function. A generic function was formulated that allows to model an extensive variety of closing laws by means of a polygonal segmented structure. An algorithm has been generated that includes this closing law as boundary condition for describing the transitory. The pressure wave shape and amplitude depends on closing function in a unique relationship.

In this work a new approach considering numerical modeling of waterhammer dissipation and attenuation is proposed. Classical Allievi liquid flow model is extended with Brunone unsteady friction model with separation of local and convective unsteady friction factor. Widely adopted approach in solving this model is treatment of the unsteady friction term as a classical source term, while the authors proposed the nonconservative formulation due to the existence of the nonconservative source term. Numerical simulations of transient flow in HPP Rijeka performed are performed by using the second order flux limited scheme with the proposed formulation. The obtained numerical results for two different operating regimes are in good agreement with measured data.

For some time, work has been underway aimed at significant simplification of the modelling of hydraulic resistance occurring in the water hammer while maintaining an acceptable error. This type of resistance is modelled using a convolution integral, among others, from local acceleration of a liquid and a certain weighting function. The recently completed work shows that during efficient calculations of the convolution integral, the effective weighting function used does not have to be characterised by large convergence with a classical function (according to Zielke during laminar flow and to Vardy-Brown during turbulent flow). However, it must be a sum of at least two or three exponential expressions so that the final results of the simulation could be considered as satisfactory. In this work, it has been decided to present certain analytical formulas using which it will be possible to determine the coefficients of simplified effective weighting functions in a simple direct way.

The paper attempts to assess the influence of closed conduits’ parameters on maximum pressure values recorded as a result of waterhammer and on the time of keeping unsteady flow with cavitation. A number of numerical tests, necessary for carrying out this research program, were performed using the aut hors’ own programs written in Matlab and based on effective cavitation transient models, which take into account unsteady hydraulic friction. In particular, the results of two key models were investigated; i.e. bubbly cavitation model (BCM) and column separation model (CSM).

This paper is devoted to the problem of energy dissipation and it concerns unsteady friction modeling of the liquid flow in hydraulic lines. One dimensional (1D) quasi-steady model of energy dissipation is in common use. It means that the loss of energy is estimated by the Darcy-Weisbach formulae. Such an approximation is close to reality only for slow changes of the velocity field in the pipe cross-section. In case of fast changes, like fast transients, e.g. water hammer, it fails. In this work the wall shear stress τ (defined as an effect of unsteady fluid friction) is presented as a sum of quasi-steady and unsteady components. The unsteady component of the wall shear stress is modeled as an convolution of the local fluid acceleration and a weighting function w(t). The weighting function, in general, makes an allowance for a relation of the historic velocity changes and the unsteady component of the wall shear stress. Primitive weighting functions have usually very complicated str...