Flow field efficiency of Mi-zi artificial reefs in different construction modes based on numerical experiments

The throwing scale of artificial reefs is one of the core issues in the construction of reefs. The throwing amount and disposal spacing of artificial reefs not only characterize the range and density, but also determine the efficiency of artificial reefs flow field effects. In our study, the flow field characteristics of seven disposal spacing (0 l, 0.5 l, 1.0 l, 1.5 l, 2.0 l, 3.0 l and 4.0 l) that is the multiple of the length of the single artificial reefs, with four throwing amounts of Mi-zi artificial reefs (2×2, 3×3, 4×4 and 5×5) were simulated using the large eddy simulation model based on the ANSYS software. Then, the relationships between the characteristics (including the relative volume, relative height and relative length) of different flow fields and the throwing amounts and disposal spacing and the target velocity ratio were studied. The results showed that when the upwelling target velocity ratio is less than 0.10, 0.10 to 0.15 and greater than 0.15 times, the maximum disposal spacing is 4.0 l, 3.0 l, 2.0 l, respectively, and there was a synergistic effect on the upwelling area. And the maximum disposal spacing is 3.0 l at all the back eddy target velocity ratios. The larger the reefing amount is, the higher the relative volume both the upwelling and the back eddy are, and the lower the average relative volume growth rate. At the disposal spacing of 0.5 l, the relative upwelling volume and the relative volume of the single artificial reefs are the largest, but the back eddy relative volume and the relative volume of the single artificial reefs are the largest at 1.5 l. The upwelling’s relative height increased at a rate of 1.01 times with the laying amount increasing and decreased at a rate of 0.90 times with the disposal spacing increasing, while the relative length of the back eddy would increase firstly and then decrease with the disposal spacing and the maximum at 1.0 l. The study provides the theoretical planning guidance for the artificial reef placement in different construction modes.