Experimental Investigation of the Turbulent Flow in a Rod Bundle Channel with Spacer Grids

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Annals of Nuclear Energy



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The performance of the CFD prediction of the flow details in the fuel assembly using Reynolds-averaged Naiver-Stokes (RANS) model is still poor. Evaluation and understanding of the complicated turbulent flow structure in the rod bundle channel with mixing devices are essential to optimize turbulence models. Therefore, the current study used the time-resolved particle image velocimetry (TR-PIV) as the measurement tool and combined with the matching index refractive (MIR) technology to obtain high-fidelity experimental data in pressurized water reactor (PWR) based 5 × 5 rod bundle channel. Mean flow properties, turbulent parameters, and spectral analysis are presented in this paper. The results show that a large velocity gradient appears downstream of the spacer grid. The turbulence intensity has been decayed sharply about 45 mm (about 4.5Dh) downstream of the spacer grid, indicated that the mixing effect of the spacer grid becomes weakened after 4.5Dh. Besides, the fluctuating velocity and instantaneous swirl strength are utilized to present the transport characteristics of the eddies downstream of the spacer grid. Combined with the power spectral density spectrum analysis of the transverse fluctuating velocity, the vortex shedding frequency of the mixing layer downstream of the spacer grid is obtained. These results indicate the existence of the quasi-periodic oscillations in the rod bundle channel. Finally, the integral scale on the rod bundle channel is calculated using the cross-correlation function of two reference points. This result reveals that the turbulence in the rod bundle channel is anisotropic.


Rod bundle; TR-PIV; Turbulence intensity; PSD


Energy Systems | Mechanical Engineering | Nuclear



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