Abstract
Dynamic mode decomposition (DMD) has been used for experimental and numerical data analysis in fluid dynamics. Despite of its advantages, the application of the DMD methodology to investigate the natural circulation in nuclear reactors are very scarce in literature. In this paper it is applied the traditional DMD and its variation, the sparsity-promoting dynamic mode decomposition (SPDMD), for analysis of temperature and velocity fields data, generated by computational simulation of an experimental setup in reduced scale, similar to a heat removal system by natural circulation of a pool-type research reactor. Firstly the numerical data is partitioned, using a space-time correlation approach, in order to identify fundamental sequences to compute the dynamic modes. Next, the DMD and SPDMD methodologies are applied over each subsequence to obtain the dynamic modes of the temperature and velocity fields. Finally the flow fields are reconstructed and compared with the original numerical data. The conclusion is that the SPDMD performs better than DMD to represent both the temperature and velocity data.
Highlights
The natural circulation is a very important matter with great interest in the nuclear reactor thermal-hydraulics
When a nuclear reactor is submitted to natural circulation conditions, a movement of the working fluid occurs from the hottest regions to the colder ones, resulting in a heat removal from the hottest regions
We present results by comparing reconstructions of numerical data that are obtained by Dynamic mode decomposition (DMD) and sparsity-promoting dynamic mode decomposition (SPDMD) methodologies
Summary
The natural circulation is a very important matter with great interest in the nuclear reactor thermal-hydraulics. Theoretical models for prediction of single-phase and two-phase natural circulation flow parameters have been developed These models have the ability to predict important flow parameters such as the pressure gradient, average phase velocities and void fractions, they are not capable to predict the flow structure itself. When a nuclear reactor is submitted to natural circulation conditions, a movement of the working fluid occurs from the hottest regions to the colder ones, resulting in a heat removal from the hottest regions. When this phenomenon is established, it has a heat exchange cycle that does not depend on any external mechanisms, for example, a pump. In a particular case of a pool type research reactor after a shutdown, the heat is transferred by natural circulation from the core to a pool water upward through the core [7]
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