Effect of large scale roughness of block ramps on dissolved oxygen efficiency in water

Abstract

Abstract Block ramps are generally characterized by super critical flow over the ramps, and the presence of roughness lying on the surface of the block ramps induces excessive turbulence, which causes some turbulent energy dissipation and air entrainment. Aeration in a block ramp is caused by the intensity of turbulence created in the water flow by surface roughness of the block ramp and hydraulic jump downstream of block ramp. Macro or large-scale roughness like boulders, as a protruding element on surface of block ramp, could increase intensify turbulence and flow aeration along block ramps. This paper presents an experimental investigation of the dissolved oxygen efficiency in block ramps with slopes of 1:3, 1:5 and 1:7, on which large-scale granular materials with different arrangement patterns were glued. Comparison of results indicated that, for both free and ramp hydraulic jumps, the block ramps with a slope of 1:3 and large-scale roughness increase the dissolved oxygen efficiency almost 20% above that of the similar smooth block ramps. By reducing of the slope of block ramps to 1:5, the dissolved oxygen efficiency of the block ramps with large surface roughness became 3 and 19% for free and ramp hydraulic jumps, respectively. However, the block ramps with 1:7 slope had corresponding dissolved oxygen efficiency of 19 and 32%, respectively. Furthermore, installation of large scale roughness with the structured arrangement have better performance to increase dissolved oxygen (DO) in comparison with the interlocked large-scale roughness.