Air‐water flows in the presence of staggered and row boulders under macroroughness conditions

[1] Free surface flow over a rough bed at steep slopes entrains large amounts of air bubbles due to the high interaction between the free surface and the bed materials. The assessment of mixed air-water flow features in the presence of a three-dimensional bed configuration from macroroughness to intermediate roughness conditions can hardly be accomplished with aeration models developed for smooth or stepped bed configurations. Two-phase flow properties were measured over rough bed materials in a setup assembled at the PITLAB center at the University of Pisa, Pisa, Italy. Coarser protruding materials were incorporated over the rough bed to intensify the aeration in the mixed air-water flow. Flow discharges ranging between 0.02 and 0.09 m2/s and slopes between 0.18 and 0.44 were tested. A detailed study of the air-water inner layer and flow features over staggered and row coarser material arrangement over the base material was carried out. Results were compared with literature data on free surface flow over smooth and stepped beds.

[1]  Nallamuthu Rajaratnam,et al.  Characteristics of Skimming Flow over Stepped Spillways , 2000 .

[2]  Brett L. Vallé,et al.  Air concentrations of submerged and unsubmerged hydraulic jumps in a bedrock step‐pool channel , 2006 .

[3]  Willi H. Hager,et al.  Development of Air Concentration on Chute Spillways , 2006 .

[4]  Jorge Matos,et al.  Air Concentration Measurements in Highly Turbulent Aerated Flow , 1997 .

[5]  Hubert Chanson,et al.  An experimental study of effects of step roughness in skimming flows on stepped chutes , 2008 .

[6]  Henry M. Morris.  Design Methods for Flow in Rough Conduits , 1959 .

[7]  Hubert Chanson,et al.  Turbulence, dynamic similarity and scale effects in high-velocity free-surface flows above a stepped chute , 2009 .

[8]  John R. Chaplin,et al.  Optical fibre probe measurements of bubbly flow in hydraulic jumps , 2005 .

[9]  Hubert Chanson,et al.  Experimental study of the air–water shear flow in a hydraulic jump , 2000 .

[10]  Kem C. Kadavy,et al.  DESIGN OF ROCK CHUTES , 1998 .

[11]  Hunter Rouse,et al.  Critical Analysis of Open-Channel Resistance , 1965 .

[12]  Serhat Kucukali,et al.  Boulder-flow interaction associated with self-aeration process , 2008 .

[13]  Luke Toombes,et al.  Hydraulics of stepped chutes: The transition flow , 2004 .

[14]  J. Bathurst.  Flow Resistance Estimation in Mountain Rivers , 1985 .

[15]  Willi H. Hager,et al.  Two-Phase Flow Characteristics of Stepped Spillways , 2003 .

[16]  Donald D. Gray,et al.  Hydraulic Performance of a Steep Single Layer Riprap Drainage Channel , 2008 .

[17]  Serhat Kucukali,et al.  Oxygen transfer in flow around and over stones placed in a laboratory flume , 2004 .

[18]  G. Pasternack,et al.  Submerged and unsubmerged natural hydraulic jumps in a bedrock step-pool mountain channel , 2006 .

[19]  R. Hotchkiss,et al.  Unobstructed and Obstructed Turbulent Flow in Gravel Bed Rivers , 2005 .

[20]  William L. Peirson,et al.  Design of Rock Protection to Prevent Erosion by Water Flows Down Steep Slopes , 2006 .

[21]  Kem C. Kadavy,et al.  ROUGHNESS OF LOOSE ROCK RIPRAP ON STEEP SLOPES , 1998 .

[22]  Stefano Pagliara,et al.  Aeration and velocity profile over block ramp elements , 2009 .

[23]  Willi H. Hager,et al.  Drawdown curve and incipient aeration for chute flow , 1998 .

[24]  Hubert Chanson,et al.  Hydraulics of skimming flows over stepped channels and spillways , 1994 .

[25]  Thimmaiah Gangadharaiah,et al.  Inception and Entrainment in Self-Aerated Flows , 1970 .

[26]  Masayuki Takahashi,et al.  Flow Characteristics of Skimming Flows in Stepped Channels , 2004 .

[27]  Richard D. Hey,et al.  Flow Resistance in Gravel-Bed Rivers , 1979 .

[28]  Willi H. Hager.  Uniform Aerated Chute Flow , 1991 .

[29]  W. C. Hughes,et al.  Hydraulic Jump Properties Over a Rough Bed , 1984 .

[30]  Hubert Chanson,et al.  Interactions between cavity flow and main stream skimming flows: an experimental study , 2004 .

[31]  Stefano Pagliara,et al.  Flow resistance in large-scale roughness condition , 2008 .

[32]  Subhasish Dey,et al.  Characteristics of Loose Rough Boundary Streams at Near-Threshold , 2007 .

[33]  Stefano Pagliara,et al.  Energy Dissipation on Reinforced Block Ramps , 2006 .

[34]  Gerhard H. Jirka,et al.  Stream Reaeration in Nonuniform Flow: Macroroughness Enhancement , 1999 .

[35]  Hubert Chanson,et al.  Self-Aerated Flows on Chutes and Spillways , 1993 .