###### Abstract  
Artificial reefs are considered to have the function of repairing and improving the coastal habitat and increasing the fishery production, which are mainly achieved by changing the regional hydrodynamic conditions. The characteristics of flow turbulence structure are an important part of the regional hydrodynamic characteristics. Different methods are used to evaluate the performance of artificial reefs according to their shape and the purpose for which the reef was built. For this study, the M-shaped unit reefs, which are to be put into the area of Liaodong Bay, were selected as the research object and have never been fully investigated before. Experimental tests were conducted to assess the effect of these M-shaped artificial reefs on the vertical and longitudinal turbulent intensity under different hydraulic conditions and geometries, and datasets were collected by using the Particle Image Velocimetry technique implemented within the experimental facility. The distribution and variation characteristics of the turbulence intensity were analyzed, and the main results obtained can confirm that in the artificial reef area, there was an extremely clear turbulent boundary. Furthermore, the area of influence of the longitudinal turbulence was identified to be larger than that of the vertical turbulence, and the position where the maximum turbulence intensity appeared was close to where the maximum velocity was measured. Finally, results demonstrate that low turbulence conditions are typically located in front of the unit reef, the general turbulence area is located within the upwelling zone, and the more intense turbulence area is located between the two M-shaped monotases. These results are extremely important, because they provide the local authorities with specific knowledge about what could be the effect of these M-shaped reefs within the area where they will be implemented, and therefore, specific actions can be taken in consideration with the geometrical setup suggested as an optimal solution within this study. Liaodong Bay; Bohai Sea; artificial reef; turbulence; particle image velocimetry; experimental modeling +
Footnote †: journal: Applied Sciences  
An Experimental Investigation of Turbulence Features Induced by Typical Artificial M-Shaped Unit Reefs  
living marine resources [8]. Over the last decade, artificial reefs have also been considered to be an effective measure to reduce the impact of human activities on coastal ecosystems and increase fishery production, and recent studies have confirmed these properties [9; 10; 11; 12; 13; 14; 15]. The flow fields generated by artificial reefs are considered to be the source of the major benefits that these structures may have on marine environments. By deploying artificial reefs into open biological environments, there will certainly be disruptions to the original smooth flow fields; however, the new currents generated may facilitate salt transport, enriching coastal ecosystems and providing vital sources and an ideal habitat for reef fish [16; 17; 18]. Different configurations can in fact influence the flows passing through these structures, generating specific currents that could aid the deposition of solid material as well as the exchange of nutrients between multiple layers, with a consequent beneficial aspect for fish expansion [19; 20]. Furthermore, these structures may also be used as protection or gathering areas by fish or other organisms, because the gentle and stable eddy currents created on the back of them could support the deposition of nutrients and function as a shield that is useful for avoiding enemies or larger predators [21; 22; 23; 24; 25; 26; 27].