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NKS Programme Area:NKS-R
Research Area:Thermo hydraulics
Report Number:NKS-154
Report Title:Analysis of Loads and Fluid-Structure Interactions in a Condensation Pool
Activity Acronym:Delipool
Authors:Antti Timperi, Timo Pättikangas, Jarto Niemi
Abstract:A simplified direct contact condensation model was implemented into the Volume of Fluid model of the Fluent CFD code. Transient three-dimensional test runs for the POOLEX experiments, where steam is blown into a water pool were performed. The model was found to provide too small condensation rate for steam when compared to experiments. In addition, the calculated back and forth oscillation of the steam water interface was much smaller than in the experiments. The model was found to be numerically quite robust. The discrepancies of the simulation, such as the too small condensation rate, could be to some extent cured by making improvements into the condensation model. As an alternative estimation method of thermohydraulic loads in condensation pools, the SILA code based on potential flow theory, was taken into use. SILA solves the pressure distribution caused by oscillating bubbles in a pool, and is easier to use and more flexible than Method of Images studied earlier. SILA has been modified for pools without an inner cylinder and test simulations for the POOLEX water pool were performed. The MpCCI FSI coupling software employs an explicit coupling scheme, which results in numerical instability in the case of the POOLEX facility. In order to improve stability, ways for implementing an implicit coupling scheme with MpCCI were examined. It was found that such a scheme is difficult to achieve without access to the source codes. An implicit coupling scheme is expected to be available with MpCCI in forthcoming years. A method was developed which can be used for analysing two-way FSI problems realistically by using only one-way coupling of CFD and structural analysis codes. In the method, the mass of the fluid is accounted for in the structural motion by adding the fluid to the structural model as an acoustic medium. Validity of the method was examined with promising results mathematically by an order of magnitude analysis and by comparing numerical results with a full two-way calculation in a simple test case and with a POOLEX experiment. The method has certain restrictions, the most important being that structural displacements have to be sufficiently small. These restrictions do not seem to be too limiting for modeling the POOLEX facility or a real pressure suppression pool. The method may have significance in many other applications as well where structural motion is small but the added mass effect of fluid is significant.
Keywords:CFD; FEM; fluid-structure interaction; steam injection; pressure suppression pool
Publication date:01 Apr 2007
ISBN:ISBN: 978-87-7893-217-4
Number of downloads:2798
Download:pdf NKS-154.pdf
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