| In the plate fuel assembly,the coolant channel is a narrow parallel rectangular channel,and the coolant forms multiple jets at the exit.At the same time,with the fuel element aging,falling off and other reasons,the coolant at the outlet is easy to form channel blockage.In the blockage and non-blocking conditions,the shear layer is prone to vortexes,backflows and other phenomena.Therefore,experimental studies on the non-blocking and blockage phenomena of jet can help us better understand the flow of coolant at the outlet and improve the end design of the plate fuel assembly.In addition,it is of great significance for maintaining the integrity of plate fuel element to study the flow redistribution caused by blockage and reveal the flow variation of blocked channel and adjacent channel.In this paper,the PMMA was used to produce the 9-channel parallel plate.The stainless steel tube and the hot-melt tube were used to build the flow loop.The camera was mounted on lifting platform,and the laser beam was adjusted by using a combined laser optics system,and the computer with software made the control system.All these equipments built the PIV system.5 long side surfaces,1 short side surface and 9 jet channels of the plane jet were photographed with a high-speed camera,and the jet flow field was obtained with different Reynolds Numbers,different planes and whether there was blockage or not.In the post-processing process,using MATLAB and other software,combined with open source code,self-programming code and open literature,including POD,PSD,FTLE and other methods,the mechanism of multiple jets was analyzed.And we also calculated the flow redistribution,obtaining a great quantity of flow information.The results show that the Reynolds number has little influence on the velocity distribution in the multiple jet.The flow field in different planes can be divided into two types: center plane jet and edge plane jet.By POD analysis,and the distribution rule of the frequency along the flow direction and the transverse direction were obtained by combining the mode coefficient with the PSD analysis of the transverse pulsation.When FTLE method is used to analyze the jet with blockage,it is found that the vortex structure above the blocking is generated alternately,and the vortex structure is merged into the mainstream in the development process.At the same time,after the central channel is blocked,the mixing of the jet in the merge region is weakened,and the transverse fluctuation frequency of the two sides of the blockage is different to some extent.The flow redistribution in the channel is calculated and the results show that the error in the calculation is quiet small.And blockage makes the flow distribution even more inhomogeneous.In a word,the PIV measurement and advancing post-processing methods are used to comprehensively reveal the movement law of the plate fuel assembly outlet flow field,providing significant reference for numerical calculation and plate fuel assembly design. |
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