EFFECT OF FREE SURFACE AND FROUDE NUMBER ON THE PROTECTION LENGTH AND TURBULENCE IN THE COMPOUND TRANSITIONS THROUGH BRIDGES

Mahmoud.I.Attia, Abdullah Alhomidan

Abstract: An experimental study was carried out to investigate the effect of free surface, Froude and Reynolds numbers on the protection length and turbulence through compound transitions using Laser Doppler, in a rectangular channel. Measurements of turbulence are carried out along the compound transition, at different contraction ratios, at different bed slopes. Vertical transition in the bed were also changed. From the results, the protection length increases with the increase of the incoming Froude number, and increases with the increase of the relative height, while it increases with the increase of the contraction ratio. The steep slope has a major effect on the protection length. Free surface has a unique role in governing the turbulence in open channel flows. Within and downstream of the transition, the turbulence occurs primarily in the wall region. Within the transition, flow tends towards the critical state (Fr approaches close to 1) with a rise in the turbulence intensities in the free surface and the wall region which may be attributed to the flow tending towards critical state. At small values of Froude number Fr = 0.22, the effect of Froude number on turbulence intensities and the free surface waves negligible.

Keywords: Turbulence intensities- Laser Doppler-Protection length-Free surface-Relative height-Contraction ratioBottom slope-Froude number

DOI: https://doi.org/10.15623/ijret.2013.0211059