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Abstact:  Hydrodynamically, there is a complex confrontation among the porous obstacles along the flow path and the fluid is significantly important Existence of obstacles in the flow path causes changes in hydraulics and hydrodynamic parameters of the flow. Among the hydrodynamic parameters that change due to the presence of obstacles in the flow path, we can mention the intensity of flow turbulence. Since turbulence is related to the energy dissipation of flow, it has always been important to study this phenomenon.one of the most important issues of river engineering is The construction of obstacles in the fluid path, especially when these obstacles are built at the river crossing. The results of studying the behavior of fluid around porous obstacles can be used in the design of gabion groins, as well as the construction of gabion obstacles in the flow path, to dissipate flow energy .In this study, the flow structure around porous groins on the side of the canal and porous obstacles in the middle of a straight channel with a fixed bed has been investigated in a laboratory. The ADV  was used to measure three-dimensional velocities and reynolds stresses around the gabion obstacles with different porosity on the side and middle of the channel The obstacles on the side of the canal act as groins and the obstacles in the middle of the canal act as obstacle consuming the energy of the stream. The velocity was measured at 1265 points for groins and it was measured at 1525  points for obstacles located in the middle of the channel .The results showed that the three-dimensional velocity components  decrease with increasing porosity in groins and obstacles. Also, the separation of flow, return flow, ..., is more severe when the obstacles is in the middle of the channel than when the groin is on the side of the channel wall.Also, the effect of porosity percentage on obstacles is much greater and clearer than on groins.And the intensity of turbulence and the extent of the area have the maximum intensity of turbulence in the obstacles in the middle of the canal is more severe than the groins in the side wall. The maximum amount of kinetic energy for obstacles is somewhat larger than for similar groins. However, the maximum turbulence intensity for the obstacles with porosity percentages of 0, 20, 40 and 60 is about 2.95, 2.4, 1.9 and 1.6 times the maximum turbulence intensity in the same groin, which is relatively large. Therefore, it can be understood that the presence of a obstacles in the middle of the channel, although it does not cause much change in flow energy, but the presence of obstacles in the middle causes the current energy dissipation up to about 2 times the current energy dissipation behind the groin.and, the process of reducing the intensity of turbulence is slower at higher porosities. Finally, The width of the zone with more turbulence intensity in the cross section for the obstacles with porosity of 0, 20, 40 and 60% is about 2.3, 2.1, 2 and 1.9 times the range in the same groin, respectively. Which in itself indicates a greater depreciation of the flow behind the obstacle.

Keywords: gabion groin, gabion obstacle, flow pattern, porosity percentage, veloci, ADV velocimeter, Intensity of turbulence, Kinetic energy of turbulence

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