Direct Numerical Simulation on Turbulent Flow over a Truncated Pyramid with a Wavy Surface in an Open Channel

摘要

We carried out direct numerical simulation for turbulent flow near surfaces of a truncated pyramid in the case with the wavy surface in an open channel. We used an immersed boundary method to express the two-dimensional truncated pyramid with a wavy surface. We compared the results in the case with the wavy surface with the results which were previously carried out on DNS for the truncated pyramid with flat surfaces. The top face of the truncated pyramid had a wavy form. It was found that the mean velocities near the top face were attenuated around the rear part of the top face in the cases both with the flat surface and with the wavy surface. The decreases in the mean velocities in the case with the wavy surface were lower than those in the case with the flat surface. On the other hand, the values of the turbulence intensities of the truncated pyramid with the wavy surface were higher than those of the truncated pyramid with the flat surface in this area. The values of the turbulence intensities in the streamwise direction decreased near the downhill face of the truncated pyramid with flat surface. On the other hand, the decreases of these values of the truncated pyramid with wavy surface were lower than those with flat surface. In addition, the values of the turbulence intensities in the upward direction increased in the area for the truncated pyramid with wavy surface. Therefore, the fluctuation of flow above the top face was large by flow of the valley region in the case with the wavy surface. The mean velocity near the downhill face was decreased, while the turbulence intensities near the downhill face were increased by this fluctuation of flow above the top face. The value of the Reynolds shear stress in the case with the wavy surface in the area near the rear part of the top face and above the downhill face was higher than that in the case with the flat surface. The area is consistent with the area where the recirculation flow had appeared intermittently in our previous experiments.