Begell House Inc.
Multiphase Science and Technology
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20
3-4
2008
FLUID-STRUCTURE INTERACTION DURING ARTIFICIALLY INDUCED WATER HAMMERS IN A TUBE WITH A BEND—EXPERIMENTS AND ANALYSES
213-238
10.1615/MultScienTechn.v20.i3-4.10
H.
Carl
Forschungszentrum Dresden-Rossendorf e.V., P.O.B. 510119, 01314 Dresden, Germany
R.
Weis
Forschungszentrum Dresden-Rossendorf e.V., P.O.B. 510119, 01314 Dresden, Germany
H.-M.
Prasser
Department of Mechanical and Process Engineering (MAVT), Swiss Federal Institute of Technology (ETHZ), ML K 13, Sonneggstrasse 3, 8092 Zürich, Switzerland
E.
Altstadt
Forschungszentrum Dresden-Rossendorf e.V., P.O.B. 510119, 01314 Dresden, Germany
Experimental and numerical investigations of artificial water hammers in a pipe with a bend are presented. At FZR, a cold water hammer test facility was used to measure the fluid pressures and the pipe wall stresses occurring during water hammers. The finite element code ANSYS was used for the numerical analysis of the experiments. The focus was put on the local distributions of pressure and stress. It could be shown that the fluid pressure and pipe wall stress exhibit complex three-dimensional structures, which is a consequence of the fluid-structure interaction. The highest stresses occur in the pipe bend. The pressure peak is lower than predicted by the Joukowsky formula.
WATER HAMMER INDUCED BY FAST-ACTING VALVES: EXPERIMENTAL STUDIES AT PILOT PLANT PIPEWORK
239-263
10.1615/MultScienTechn.v20.i3-4.20
A.
Dudlik
Fraunhofer UMSICHT, Oberhausen, Germany
H.-M.
Prasser
Department of Mechanical and Process Engineering (MAVT), Swiss Federal Institute of Technology (ETHZ), ML K 13, Sonneggstrasse 3, 8092 Zürich, Switzerland
A.
Apostolidis
Fraunhofer UMSICHT, Oberhausen, Germany
A.
Bergant
Litostroj E.I. d.o.o., Slovenia
The water hammer and inertia-driven cavitation hammer phenomena caused by the activation of fast-acting valves were studied in a pipeline test facility at Fraunhofer UMSICHT in the context of the EURATOM project WAHALoads. The main goal of the project is the prediction of the loads on equipment and support structures. The presented experiments tackle some scenarios typical for power plants and supply material for code validation with regard to the modeling of both thermohydraulic effects and fluid-structure interaction. The test facility Pilot Plant Pipework, representing an approximately 230 m long experimental pipeline, was upgraded in order to allow experiments at system pressures of up to 30 bar at maximum temperatures of about 180° C. The test rig was further equipped with a test segment that simulates a piping system and the associated supports typical for a (nuclear) power plant. For a better understanding of thermohydraulic processes during cavitation behind the fast-acting valve, novel instrumentation was applied. Wire-mesh sensors as well as local void probes were equipped with integrated microthermocouples and used for the local instantaneous measurement of both void fractions and fluid temperature. The fast temperature measurement combined with the instantaneous detection of the passage of the gas-liquid interface measurement reveals insights into the condensation heat transfer controlling the speed of the void collapse in the case of a condensational water hammer.
SPONTANEOUS WATER HAMMERS IN A STEAM LINE IN THE CASE OF COLD WATER INGRESS
265-289
10.1615/MultScienTechn.v20.i3-4.30
H.-M.
Prasser
Department of Mechanical and Process Engineering (MAVT), Swiss Federal Institute of Technology (ETHZ), ML K 13, Sonneggstrasse 3, 8092 Zürich, Switzerland
Gy.
Ezsol
KFKI-AEKI Budapest, PO Box 49, H1525 Budapest 114, Hungary
G.
Baranyai
KFKI-AEKI Budapest, PO Box 49, H1525 Budapest 114, Hungary
T.
Suhnel
Forschungszentrum Dresden Rossendorf, e.V., PO Box 510119, 01314 Dresden, Germany
Some of the accident scenarios discussed for the Russian type pressurized water reactors VVER-440 assume an overfeed of the secondary side of the steam generators by water coming either from the primary side or from the feedwater system. This may happen, for example, in the case of a leakage from the primary to the secondary side, as well as during earthquakes, and can lead to water ingress into the main steam lines, where condensation-induced water hammer may be the consequence. The present work was initiated to study this phenomenon experimentally. For this purpose, the PMK-2 test facility of KFKI-AEKI Budapest, an integral thermohydraulic model of a VVER-440/W213, was extended by a steam-line model, which is equipped with a novel two-phase flow instrumentation as well as fast pressure and strain-gauge transducers. The applied mesh sensor developed by Forschungszentrum Dresden Rossendorf allows a visualization of the transient flow section during the water hammers. Local void probes detect the propagation of slugs along the pipe. The applied new kind of probe is equipped with microthermocouples to provide local instantaneous temperature measurements along with phase detection. This allows assessing temperature gradients at the boundary between the water and steam. The paper describes the test facility and the new instrumentation. The results of the first tests are presented and discussed. The work is part of the WAHALoads project, which was performed within the fifth EU framework program. The objective of the project was to improve the prediction of loads on equipment and support structures of nuclear power plants that are caused by water hammers and shock waves.
TWO-FLUID MODEL OF THE WAHA CODE FOR SIMULATIONS OF WATER HAMMER TRANSIENTS
291-322
10.1615/MultScienTechn.v20.i3-4.40
J.
Gale
Reactor Engineering Division, Jozef Stefan Institute, Jamova cesta 39, 1000, Ljubljana, Slovenia
Iztok
Tiselj
Reactor Engineering Division, Institut Jozef Stefan, Slovenia
A.
Horvat
Reactor Engineering Division, Jozef Stefan Institute, Jamova cesta 39, 1000, Ljubljana, Slovenia
A new thermal hydraulic computer code, WAHA, was developed within the WAHALoads project of the European Union Fifth Framework Program. The code's aim is simulation of water hammer transients in piping systems and is based on a one-dimensional, two-fluid, six-equation model of the two-phase flow. The WAHA code can describe two-phase flows in long piping systems (1D geometry) with variable cross section. The code contains correlations for heat, mass, and momentum transfer between the phases and for wall friction in dispersed and horizontally stratified flow regimes. The WAHA code physical model takes into account the elasticity of the pipe through Korteweg's equation; it takes into account water properties and the unsteady wall friction, and contains a set of subroutines for calculation of forces on the piping system. Special models in the WAHA code are implemented for abrupt area changes and branches, for constant pressure (tank), for constant velocity (pump), and for valve closure boundary conditions. The physical model and the main correlations and closure laws, which are applied in the present work, are described and verified with several experiments. The code was successfully applied for simulations of two-phase critical flow, several column-separation types of water hammer, and for condensation-induced water hammer experiments.
NUMERICAL SCHEME OF THE WAHA CODE
323-354
10.1615/MultScienTechn.v20.i3-4.50
Iztok
Tiselj
Reactor Engineering Division, Institut Jozef Stefan, Slovenia
A.
Horvat
Reactor Engineering Division, Jozef Stefan Institute, Jamova cesta 39, 1000, Ljubljana, Slovenia
J.
Gale
Reactor Engineering Division, Jozef Stefan Institute, Jamova cesta 39, 1000, Ljubljana, Slovenia
This paper describes the numerical scheme used in the WAHA code that was developed within the WAHALoads project for simulations of fast transients in 1D piping systems. Two-fluid model equations described in a companion paper entitled "Two-Fluid Model of the WAHA Code for Simulations of Water Hammer Transients," are solved with an operator splitting procedure: The nonconservative characteristic upwind scheme is used to solve the hyperbolic part of the equations with the nonrelaxation source terms, while the relaxation source terms are treated in the second step of the operator splitting procedure. Water properties are calculated with a newly developed set of subroutines that use pretabulated water properties. Special models that were developed for treatment of the abrupt area changes and branches in the piping systems are described. Various test cases, which were used to test the accuracy of the basic numerical scheme and the accompanying numerical models, are described and discussed together with the typical results of simulations.