بررسي برهم كنش شكل هاي بستر شني با تاج مسطح و پوشش گياهي ديوار بر مولفه هاي جريان آشفته

چكيده انگليسي :

Investigation of Interaction of Straight Crested Gravel Bedforms and Vegetated Banks on Turbulent Flow Components Shahrzad Davarpanah Jazi s davarpanah@ag iut ac ir Date of submission 13 7 2011 College of Agriculture Dept of Water Eng Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor s Name and Email address Dr Hossein Afzalimehr hafzali@cc iut ac ir Dr Abdoreza Kabiri Samani akabirisamani@cc iut ac ir AbstractRivers have always been the main sources in providing water demand for human kind and the basicelement in population development One of the ways of understanding rivers behavior is to investigatetheir flow structure and bedforms On the other side vegetation exists widely in natural river systemscreating roughness on channel walls and flood plains which affects the geometrical shape hydraulics andflow resistance that follows by sediment transport Considering the importance of bedforms such as dunesin sediment transport control turbulence production and resistance to flow studying the details ofinteraction of bedforms vegetated banks and flow structure seems to be necessary In this study theinfluence of straight crested gravel dunes and vegetation cover on channel banks were investigated onflow structure To reach this purpose seven fixed artificial 2 D straight crested dunes were built along arectangular flume at the HydraulicV Laboratory of Isfahan University of Technology Iran The flume hada length width and depth of 8m 0 4m and 0 6m respectively The graded gravel particles used forbuilding the dunes had a median diameter of d50 10mm and the trapezoidal shape of the dunes were keptconstant through the experimental study The stems of Johnson grass with a median diameter of 2 8mmwere used to simulate vegetation cover on the flume walls With respect to the fact of having fullydeveloped flow located after the fifth dune experimental measurements were conducted over the fifth andsixth dunes In total 3 runs were performed over dunes with a wave length height angle of repose andflow depth of 0 96m 0 04m 28 degrees and 0 28m respectively In the first case 17 velocity profiles andin the second and the third case 21 velocity profiles were measured The experiments were all performedwith a discharge of 0 024m3 s The instantaneous three dimensional velocity components were measuredusing a down looking Acoustic Doppler Velocimeter ADV which was developed by the NORTEKCompany Velocities were recorded for each point with a sampling frequency of 200Hz and the samplingvolume of 5 5mm The sampling duration at each point was 120 seconds Ultimately more than45 400 000 velocity data were collected and they were filtered by WinADV software An important resultin this study was that in gravel bedforms with straight crest unlike the sharp crest beforms in both casesof with and without vegetation cover no negative velocities were observed According to the horizontalvelocity contour maps in the case of no vegetation cover the least velocity value was zero which tookplace at a small region on the lee side of the dune Also in the case of with vegetation cover the leastvelocity value was zero too but its location had moved down stream at the dune s trough Observing thenegative vertical velocity value in both cases of with and without vegetation cover through a dunewavelength was another sign of not occurring separation in straight crested dunes The Reynolds stressvalues increased in the case of with vegetation cover comparing to the case of without vegetation cover This can be related to the increment of flow resistance in the presence of vegetation cover on the wall Key Words Straight crested gravel dune Reynolds stress Vegetated walls Turbulent flowcomponents Turbulence intensities

داورپناه جزي، شهرزاد

بررسي برهم كنش شكل هاي بستر شني با تاج مسطح و پوشش گياهي ديوار بر مولفه هاي جريان آشفته

تلماسه شني با تاج مسطح , تنش رينولدز , شدت آشفتگي