On the Behavior of Vortical Structures in a Single-Flood Plain Open Channel.

Abstract

Multi-section flow visualization technique and Mass-Consistent model are employed to picture the vortical structures and their behavior in a comparatively wide single-flood plain channel. Repeated cycles of photography enables us to calculate both mean and instantaneous flow characteristics. Investigations of vortical structures have revealed that in the main channel, close to the bed, vortices with axes in the spanwise direction are dominant; farther above the bed close to the junction border, vortices with vertical axes become more significant. They are connected to the vortices in the flood plain. At the neck of a continued typical vortex (under the connection of two limbs) induced velocity acts against the main flow. This typical vortical structure contributes to continuous momentum, mass and energy transfer from the main channel to the flood plain and vice versa and it is responsible for the reduction of compound channel capacity.1) Myers, W. R. C. and Brennan, E. K.: Flow Resistance in Compound Channels. J. Hydr. Res., 28, No. 2, pp. 141-155 (1990)2) Wormleaton, P. R., Allen, J. and Panos, P. H.: Discharge Assessment in Compound Channel Flows. J. Hydr. Div., ASCE 108, No. HY9, pp. 975-994 (1982)3) Prinos, P., Townsend R.and Tavoularis, S.: Structure of Turbulence in Compound Channel Flows. J. Hydr. Eng., ASCE 111, No. 9, pp. 1246-1261 (1985)4) Acarlar, M. S. and Smith, C. R.: A study on Hairpin Vortices on the Laminar Boundary Layer, Part 1 : Hairpin Vortices Generated by a Hemisphere Protuberance. J. F. Mech. 175, 1-41 (1987)5) Head, M. R. and Bandyopadhyay, P.: New Aspects of Turbulent Boundary-Layer Structure. J. F. Mech. 107, 297-338 (1981)6) Agui, J. C. and Jimenez, J.: On the Performance of Particle Tracking. J. F. Mech. 185, 447-468 (1987)7) Dimotakis, P. E., Debussy, F. D. and Kooches-fahani, M. M.: Particle Streak Velocity Field Measurements in a Two-Dimensional Mixing Layer. Phys. Fluids 24, 995-999 (1981)8) Kawanishi, K., Maghrebi, M. F., Yokoshi, S.: An Instantaneous 3-D Analysis of Turbulent Flow in the Wake of a Hemisphere. Bound. Lay. Meteo., 64, No. 1/2 (1993)9) Naot D. and Rodi, W.: Calculation of Secondary Currents in Channel Flow. J. Hydr. Div., ASCE 108, pp. 948-968 (1982)10) Tominaga, A. and Nezu, I.: Turbulent Structure in Compound Open-Channel Flows. J. Hydr. Eng., ASCE 117, No. 1, pp. 21-41 (1991)11) Knight, D. W. and Hamed M. E.: Boundary Shear in Symmetrical Compound Channels. J. Hydr. Eng., ASCE 110, No. 10, pp. 1412-1430 (1984)