برهم كنش پوشش گياهي ، شكل هاي بستر و ساختار جريان بر توزيع هاي سرعت و شدت هاي توربلانس

چكيده انگليسي :

Interaction of Vegetation Cover Bed Forms and Flow Structure on Distributions of Velocity and Turbulent Intensities Abstract In applied fluvial geomorphology dunes are important bed forms and significantly influence the features of turbulence The effect of gravel dunes on a turbulent flow is important in determining the formation of bed forms resistance to flow and sediment transport in coarse bed rivers Also Vegetation exists widely in natural river systems especially in flood plains The turbulent flow structures over fixed 2D dunes have been investigated by many scientists However no research has been reported about the interaction of bed form and vegetated channel banks on flow structure In this study the influence of the bed forms and vegetation on channel banks on velocity Reynolds stress distributions and turbulent intensities have been investigated The experiments have been carried out in a recirculating flume at the Hydraulics laboratory of Isfahan University of technology in Iran The flume is 8 m long 0 4 m wide and 0 6 m deep The stems of rice with a median diameter of 2 7 mm were used to simulate vegetation on flume walls In total 4 runs were selected In the first case the influence of vegetation on flume walls and flat bed on location of fully developed flow has been investigated In the second and third case experimental measurements have been conducted over the fifth and sixth dunes in a series of seven of 2 dimensional asymmetric gravel dunes which the 0 08m height and the 0 96 m wavelength was preserved constantly and the chosen slip face for lee side were respectively 28 and 35 The influence of different angles of lee slope of gravel dunes on the characteristics of flow in vegetated flume has been discussed In the final case conditions were similar with the second case only the vegetation was removed The dunes have been built with graded gravel particles which have a median diameter of d50 10 mm The mean flow depth h is kept constant as 20 cm for all the experiments The experiments are performed with a discharge Q 0 024 m3 s A down looking acoustic Doppler velocimeter ADV has been used to measure the instantaneous three dimensional velocity components Velocities have been recorded for each point with a sampling frequency of 200 Hz and the sampling volume of 5 5 mm The sampling duration at each point was 120 seconds A total of 7 velocity profiles in first Run 20 velocity profiles in second Run 22 velocity profiles in third Run and 16 velocity profiles in first Run were taken Ultimately more than 44 millions velocity data were collected The results show that when flow separation commences streamlines are directed towards the bed and very large negative vertical velocities occur just downstream of the crest Positive vertical velocities within the separation cell show the presence of a strong circulation pattern especially near the dune slip face Additionally the bed shear stress first increases reaching a maximum value at the stoss side of the dune Thereafter it diminishes and reaches a minimum value at the dune crest The results also indicate that the position of maximum turbulence intensity is advected along the mean flow streamlines around the region of separated flow bringing turbulent fluid from the free shear layer immediately downstream of the dune crest toward the bed Finally the results reveal that the high turbulence intensity and high Reynolds stress are characterized by low velocity in the recirculation region whereas the region of the outer flow is dominated by a high velocity and lower Reynolds stress and turbulence intensity Key Words Gravel dune Lee slope angle of dune Vegetated walls Reynolds stress Turbulence intensities

نصيري ده سرخي، الهام

برهم كنش پوشش گياهي ، شكل هاي بستر و ساختار جريان بر توزيع هاي سرعت و شدت هاي توربلانس

تلماسه شني , زاويه وجه پايين دست تلماسه , تنش رينولدز , شدت هاي آشفتگي