Flow and turbulence characteristics at downstream of inclined cylinder group

Rivers are ecologically fragile balanced formations based on morphological and biological effects. Vegetation is one of the most important components of this fragile balance. Aquatic vegetation has an impact on bank stability, sediment transport and morphological characteristics beside the ecological diversity. River ecosystems are faced with human based impacts for energy generation, water supply or flood control depending on highly increasing population and developing industry. Nowadays, exchanging these artificial impacts with natural arrangements by understanding the river ecosystem and river dynamics is a hot topic. For this purpose there are dozens of researches in the field of the effects of vegetations on flow, turbulence structures and sediment transportation. In this research, 12 experiments conducted with 4 different erection angles of group cylinders as 90⁰ (vertical), 75⁰, 45⁰ and 60⁰ and 3 different discharges (Q1=20.5 l/s, Q2=40.83 l/s and Q3=56.8 l/s) for each condition. Experiments performed with rigid cylinders that positioned on a wooden plate (0.5x1.0x0.1m as shown in Figure 3.2) in a channel which has L=18m in longitudinal length, B=0.5m width and 0.5m depth. Side walls and bed of the channel are constructed of glass and smooth concrete, respectively. According to these experiments, time averaged velocity distribution, normalized Reynolds stresses, turbulence kinetic energy and energy spectra have been computed. As a result of experiments, it is concluded that the distribution of time averaged velocity component does not depend on discharge. Time average velocity component mostly depends on the angle of the cylinder groups. In the case of vertical and α=75⁰positions, velocity has lower values close to bed and it is getting increased by the distance from the wall. For the position of α=45⁰ and α=60⁰, because of the inclination of cylinders, velocity component close the bed increases and surface part decreases. Reynolds normal stresses is dominant through the x and z axis compared to y axis for all the experiments. Reynolds shear stress values decreases when the erection angle of cylinder groups decreases because of the modified hydrodynamic form of the cylinders.