Visualisation of transient cavitating flow in piping systems

The paper deals with the visualisation of transient cavitating flow in piping systems. A high-speed video-system is used to record liquid column separation events in an experimental apparatus. The apparatus comprises a straight 37.2 m long sloping pipeline of 22 mm internal diameter, connecting two pressurised tanks. A discrete vapour cavity and vaporous cavitation zone were observed in the pipeline following downstream end rapid valve closure. The results of measurements (flow visualisation and pressure measurement) are compared to the discrete gas cavity model results. There are minor discrepanlfies between the computed and measured resultsANTON BERGANT - ANGUS R. SIMPSO

Experimental and numerical analysis of water hammer in a large-scale PVC pipeline apparatus

This paper investigates the effects of the pipe-wall viscoelasticity on water-hammer pressures. 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-pipe-valve system with a 275.2 m long DN250 PVC pipeline. Rapid closure of a manually operated ball valve at the downstream end generated water hammer. Computed results are compared with experimental runs. Calibrated creep functions have been obtained using optimization in conjunction with an inverse hydraulic transient solver and these are used in the simulations. It is shown that the incorporation of both unsteady skin friction and viscoelastic pipe wall mechanical behaviour in the hydraulic transient model contributes to a favourable fitting between numerical results and observed data. Keywords: Water hammer, Unsteady Skin Friction, Viscoelasticity, Pipeline Apparatus, PVC Pipe

Experimental and numerical analysis of water hammer in a large-scale PVC pipeline apparatus

This paper investigates the effects of the pipe-wall viscoelasticity on water-hammer pressures. 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-pipe-valve system with a 275.2 m long DN250 PVC pipeline. Rapid closure of a manually operated ball valve at the downstream end generated water hammer. Computed results are compared with experimental runs. Calibrated creep functions have been obtained using optimization in conjunction with an inverse hydraulic transient solver and these are used in the simulations. It is shown that the incorporation of both unsteady skin friction and viscoelastic pipe wall mechanical behaviour in the hydraulic transient model contributes to a favourable fitting between numerical results and observed data. Keywords: Water hammer, Unsteady Skin Friction, Viscoelasticity, Pipeline Apparatus, PVC Pipe

A discrete gas-cavity model that considers the frictional effects of unsteady pipe flow

Abstract not availableAnton Bergant, Uroš Karadžić, John Vitovský, Igor Vušanović, Angus R. Simpso

Developments in pipeline column separation experimentation

This paper summarises developments in column separation experimentation in pipes at the University of Adelaide, South Australia. An experimental apparatus with a 37.2 m copper pipe of 22 mm diameter has been constructed. A very fast closure ball valve has been developed which provides a closure time of 5 to 10 milliseconds. Two problems in the development of the experimental apparatus are discussed in detail. First, a problem was encountered with the placement of two 150 mm long How visualisation polycarbonate sections in the pipeline. The discrete vapour cavity numerical model is used to simulate the effect of the presence of the polycarbonate sections in the experimental apparatus. Second, problems in obtaining accurate pressure readings from strain-gage type pressure transducers have also occurred. Analysis of the experimental results has led to the development of solutions to overcome these problems when investigating column separation in pipelines.Angus R. Simpson & Anton Bergan

Analysis of beat phenomena during transients in pipelines with a trapped air pocket

Trapped gas pockets may cause severe operational problems in liquid piping systems. The severity of the resulting transients depends on the size and position of the trapped air pocket. Previous numerical simulations by the authors have indicated that a beat is possible to develop for ‘medium’ size air pockets. This paper investigates the beat phenomenon in detail, both theoretically and experimentally. Trapped air pockets are incorporated as boundary conditions (discrete gas cavities) into two distinct numerical solution schemes: (1) the method of characteristic scheme (MOC) and (2) a conservative solution scheme (CSS). The classical discrete gas cavity model (DGCM) allows gas cavities to form at computational sections in the MOC. A discrete gas cavity is governed by the water hammer compatibility equations, the continuity equation for the gas cavity volume, and the equation of state of an ideal gas. A novel CSS-based DGCM solves the system of unsteady pipe flow equations and respective state equations for four dependent variables (pressure, density, cross-sectional area, flow velocity) rather than two variables (pressure, flow velocity) in the classical MOC approach. In the MOC-based DGCM, the Courant number is equal to unity. This condition is difficult to fulfil (without using interpolations) in complex pipe networks without modification of wave speeds and/or pipe lengths. The CSS-based DGCM offers flexibility in the selection of computational time and space steps, however, the numerical weighting coefficients in the scheme should be carefully selected. Both models incorporate a convolution-based unsteady friction model. Experimental investigations of beat phenomena have been carried out in the University of Adelaide laboratory apparatus (reservoirpipeline- valve system). A trapped air pocket is captured at the midpoint of the pipeline in a specially designed device. The transient event is initiated by rapid closure of a side-discharge solenoid valve. Predicted and measured results are compared and discussed. It is shown that the fully-developed beat is strongly attenuated by unsteady friction and not so by steady friction

Closure to “Systematic Evaluation of One-Dimensional Unsteady Friction Models in Simple Pipelines”

J. P. Vítkovský, A. Bergant, A. R. Simpson and M. F. Lamber

A boundary layer growth model for one-dimensional turbulent unsteady pipe friction

Unsteady flow in pipe networks is efficiently modelled using a one-dimensional flow approximation. It is general practice in engineering to assume a quasi-steady state approximation of the friction for unsteady pipe flows. The result of this approximation is an under-estimation of the damping during fast transient events. To remedy this shortcoming, an unsteady friction model is often employed. Unsteady friction models for laminar flow can be theoretically determined and have been successfully used for many years. However, the same cannot be said for unsteady friction in turbulent flows. A number of empirical unsteady friction models have been formulated, but only perform well for certain unsteady transient event types. This paper presents a new unsteady friction model for turbulent flows based on the growth and destruction of the boundary layer during a transient event.MF Lambert, JP Vítkovský, AR Simpson & A Bergan