An experimental study on turbulent flow in a fuel rod bundle with mixing vane spacer grid

An experimental study has been carried out to investigate the structure of the flow through subchannels of rod bundle and spacer grid with mixing vanes. Two-dimensional velocity fields and turbulence intensity were measured using LDV in water of normal temperature and pressure in several Reynolds number. In axial and lateral velocity profile, basic flow structures were maintained with respect to the numbers and spatial position of peak points. In small flow rate the axial velocities in the center of subchannel and the gap between the rods showed large differences, but in higher flow rate, the velocity differences between gap and center were relatively small that could be understood by strong turbulent mixing. The distribution of axial turbulence intensity showed relatively large gradient along the lateral direction in the case of low flow rate. The mechanism of the decay of turbulence intensity in streamwise direction was similar in several flow rate with Sreenivasan's function. The swirl caused by the mixing vanes in subchannel could be observed in lateral velocity profiles. In the viewpoint of swirl ratio, swirling effect propagated well downstream in the flow of high Reynolds number. The thermal mixing in subchannels was analogized with similar mechanism