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

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

Tracking of urban aerosols using combined LIDAR-based remote sensing and ground-based measurements

A measuring campaign was performed over the neighboring towns of Nova Gorica in Slovenia and Gorizia in Italy on 24 and 25 May 2010, to investigate the concentration and distribution of urban aerosols. Tracking of two-dimensional spatial and temporal aerosol distributions was performed using scanning elastic LIDAR, operating at 1064 nm. In addition, PM<sub>10</sub> concentrations of particles, NO<sub>x</sub> concentrations and meteorological data were continuously monitored within the LIDAR scanning region. Based on the data we collected, we investigated the flow dynamics and the aerosol concentrations within the lower troposphere and found an evidence for daily aerosol cycles. We observed a number of cases with spatially localized increased LIDAR returns, which are associated with the presence of point sources of particulate matter. Daily aerosol concentration cycles were also clearly visible with a peak in aerosol concentration during the morning rush hours and daily plateau at around 17:00 Central European Time. We also found that horizontal atmospheric extinction at the height of 200 m, averaged in limited region with a radius of 300 m directly above the ground-based measuring site, was linearly correlated to the PM<sub>10</sub> concentration with a correlation coefficient of 0.84. When considering the average of the horizontal atmospheric extinction over the entire scanning region, a strong dependence on traffic conditions (concentration of NO<sub>x</sub>) in the vicinity of the ground-based measuring site was observed

Simulation of water column separation in Francis pump-turbine draft tube

The paper presents the modelling, simulation and analysis of the transient behaviour of a 340 MW pump-turbine in case of emergency shutdown in turbine mode with focus on possible draft tube water column separation. The model of a pumped storage power plant with simplified layout is presented. This model includes a penstock feeding one 340MW pump-turbine with the related rotating inertia and a tailrace tunnel. The model of the tailrace tunnel allowing for water column separation simulation is introduced. The simulation results of the transient behaviour of the pump-turbine in case of emergency shutdown in generating mode, with and without downstream water column separation model are presented for different degree of severity triggered by the submergence and the tailrace tunnel length. The amplitudes of the pressure peaks induced by the cavity collapse are analysed with respect to the pressure drop magnitude and tailrace dimensions. The maximum and minimum pressure amplitudes obtained along the tailrace tunnel are analysed for different test case conditions

Unsteady skin friction experimentation in a large diameter pipe

Experimental data for the validation of theoretical models of unsteady skin friction are limited and are available only for a few low Reynolds number flow cases. There is a strong need for detailed measurements in flows at high Reynolds numbers. In addition, there is a need for a wider range of well-controlled acceleration/deceleration rates and detailed visualization of flow structure and profiles. To address these needs, a large-scale pipeline apparatus at Deltares, Delft, The Netherlands, has been used for unsteady skin friction experiments including acceleration, deceleration and acoustic resonance tests. The apparatus consists of a constant head tank, a horizontal 200 mm diameter pipe of changeable length (44 to 49 metres) and a control valve at the downstream end. In addition to standard instrumentation, two distinctive instruments have been used: hot-film wall shear stress sensors ("direct" measurement of wall shear stress) and a PIV set-up for measurement of unsteady flow profiles. This paper describes the test rig, the instrumentation layout and the test programme. Finally, some initial test results are presented and discussed