Masashi Yano

EFFECTS OF BED SHAPE ON TURBULENT STRUCTURE IN SIDE-CAVITY OPEN-CHANNEL FLOWS

Measurements of instantaneous flow fields in and around side cavity open-channel flows were conducted with a PIV. The aspect ratio (the streamwise length of the side cavity/the lateral length of the side cavity) was set to 2. Two kinds of experiments were carried out. One is the rigid smooth bed condition. The other is movable sands bed condition. In the movable case, the experiments were conducted after the developing the equilibrium sand wave. It was found that a large scour is generated around the edge of the spur dikes. This is because the flow velocity increases there. In contrast, a deposition is generated just behind the sand wave in the main-channel. The vector patterns of time-averaged flow velocities are quite different from each other (movable case and rigid case). In the rigid case, a large horizontal vortex is generated by the shear instability between the main channel and the side cavity. On the other hand, vortex in the side cavity is reduced by the effect of the main flow in the movable case. As the results, turbulent intensity, Reynolds stress and mass and momentum exchange rate noticeably change in comparison with the rigid case.