Flow resistance and turbulent structure in an open channel with longitudinally continuous side cavities.

Takayuki Tanaka, Terunori Ohmoto

Thursday 2 july 2015

12:51 - 12:54h at Amazon (level 1)

Themes: (T) Water engineering, (ST) River and coastal engineering, Poster pitches

Parallel session: Poster pitches: 11B. River Engineering

The cavity zone along riverside is expected to produce native habitats of various ecosystems and water-friendly environment. However, effects of side cavities on flow resistance and turbulent flow structures are ambiguous, because the side cavity generates the complex separated vortices. In this paper, the flow resistance and turbulent flow structure in open channel flow with longitudinally continuous side cavities were examined experimentally. The experiments were conducted using a circulating variable-slope flume made of acrylic resin measuring 10 m long, 40 cm wide and 20 cm high. The blockers were placed along the left sidewall of the flume. The width Bw of the cavity is 10 cm, and the length Ls of blockers in the stream direction is 30 cm. The length of a cavity in the stream direction is represented by Lc, and the ratio between this cavity length in the stream direction and the cavity width is varied Lc/Bw = 0 to 5. The investigation of flow structures involved the measurement of water surface oscillation and flow velocity at multiple points. Water surface oscillations were measured with ultrasonic water level sensors and flow velocity at multiple points was measured simultausneoly by particle image velocimetry (PIV). Examinations of flow resistance relative to changes in the aspect ratio of cavity, the flow resistance significantly depended on aspect ratio of side cavity. The results of examination of momentum transport characteristics indicate that the maximum value of water depth occurred, momentum transport was most active at or boundaries between the cavity and the main flow region. Therefore, the flow resistance significantly depended on aspect ratio of side cavity and the reason could be explained by the difference of momentum transport through the interface between the side cavity and main flow region.