Abstract
Investigations of the flow structure on the benchmark “cube” under conditions of natural convection caused by a vertical temperature gradient are performed using a low cost PIV-measuring system with continuous laser. The obtained velocity fields were processed with POD method to obtain typical structures (modes) in the flow. It is shown that the steady flow can be described by combination of the first three modes. It is demonstrated that only starting with the third mode there is a significant change in the spectra of the amplitude coefficients of the modes, the peak shifts to the region of higher frequencies. Thus accounting for this mode is essential for describing turbulent processes in the system and verification of numerical calculations. Comparison with the results of the LES simulation performed using the Ansys CFX package (taking into account the results of processing the experimental data by the POD method) demonstrated good agreement both in the structure of the modes and in their frequency spectra.
Highlights
For processes in power plants, the task of predicting temperature fields in non-isothermal flows is of current importance
Experts from CFD4NRS recommend an experiment on investigation of the natural convection of air inside a cubic cavity with a given temperature difference of opposite vertical walls for verifying experiments that model the conditions of natural convection
All the measured velocity fields were filtered and merged into a three-dimensional matrix of 61x62x9587 points. 3.2 Velocity field analysis As mentioned above, the focus of velocity field investigation was on two aspects: the first is the settling time to the flow, and the second is the separating of the characteristic patterns of the flows and their analysis using Proper orthogonal decomposition (POD) methods
Summary
For processes in power plants (including nuclear), the task of predicting temperature fields in non-isothermal flows is of current importance. The first numerical calculations of convection in a cubic cavity with a vertical temperature difference were carried out for moderate values of the Rayleigh number (3.5⋅103 ≤ Ra ≤ 6⋅104) [3,4,5,6]. In the numerical analysis during verification and comparison it is necessary to take into account the time factor of development or establishment of flows. It can be investigated by comparing the averaged fields for different averaging times.
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