PIV Research On The Flow Structure Of The Open Channel With Rigid Plants

Aquatic plants is an important part of the river,which can improve the river ecology and stabilize the riverbed,but it also changes the flow structure.In this paper,the flow velocity in a laboratory flume with organic glass rods was measured by Particle Image Velocimetry(PIV)to study on the flow structure of the open channel with rigid plants.The characteristics of the average velocity,turbulent intensity and Reynolds shear stress were studied when the plant densities and the submergence degree were different.The main research works were carried out as follows:(1)The three flow characteristics were change when the plant density was different.The denser the plants were,the stronger the flow resistance was to reduce the flow velocity.However,at the upper non-vegetated layer,the flow velocity was gradually increased,and at a distance from the surface,it became lager than the velocity of lower density.The maximum of turbulence intensity appeared near the top of the plants.From the height of half of the plants to the surface of the flow,the turbulence intensity of the high density is greater than it of the low density,and below it the comparison did not seem obvious.The Reynolds shear stress was increased between the height of half of the plants and flow surface as plant density increases,and it was close to 0 below the half height of the plants.(2)The three flow characteristics were change when the submergence degree was different.The smaller the submergence,the greater the flow velocity was at the same height from the bottom of the flume.The maximum of turbulence intensity increased with the decrease of the submergence degree,but the turbulence intensity of the upper non-vegetated layer decreased gradually to less than it of high submerged degree.The variation law of Reynolds shear stress was similar to that of the turbulence intensity.When the plant is emerged,the flow velocity between the plants increased,and the turbulence intensity was obviously greater than that of the flume without plants.The Reynolds stress is small,and it was not much change compared with the non-plant condition.(3)Comparing the surface layer velocity distribution pattern with different plant density,different submergence degree and different mean velocity in section,it can come to a conclusion with the effect law that above-mentioned operating conditions to the surface layer velocity distribution pattern.Chose several kinds of typical operating condition compared with three kinds of empirical formulas of flow velocity distribution,discover that a single logarithmic distribution cannot fully meet the expression of the surface layer velocity distribution,only in good agreement for velocity distribution without obvious turning point.In the case of velocity distribution have obvious turning point,from the turning point to surface,the difference between the calculated value and the measured value is great,and the distribution forms are obviously different.The research results of this paper have certain reference significance for the study on the structure of the open channel flow with plants.