Numerical simulation and PIV experimental study of the effect of flow fields around tube artificial reefs

The intensity and scale of flow fields around artificial reefs are key factors to attracting fish. Three kinds combination of reefs (1, 3, and 6), were numerically analysed under five different velocities (4.5, 9.0, 13.5, 18.0, 22.5 cm s(-1)) by renormalization group (RNG) k-epsilon turbulent model. The results of numerical simulation are consistent with data obtained from a particle image velocimetry (PIV) experiment. The mean error is less than 10%. Based on the experimental verification, the effects of a variable number of reefs on the flow field are simulated using Fluent code. The intensities and scales of upwelling, which are described by their heights and areas, intensify with number increase of reefs. Relevant relational equations are obtained through regression analysis; all correlation coefficients exceed 0.990. The scale and intensity of the back vortex, which are measured by the length and area of the vortex, also intensify with number increase of reefs. Two relevant relationship equations are obtained; all correlation coefficients exceed 0.995. The unit reef effect is analysed using a simulation method. The numerical results indicate that a greater unit artificial reef effect is obtained when five reefs are involved, and the ratio (r) of reef unit height (h) to water depth (d) is 0.224 (r=h/d).