Experimental Study On Flow Structure In Open Channel With Dense Roughness

Roughn bed surface of Open channel flow structure is the important content of physical model test research,but the existing research on the flow structure analysis are mainly composed of a single point of contact information,is not yet clear close add quantitative influence of the structure of face rough bed open channel flow.To reve al the bed surface is rough quantitative influence regularity of turbulence parameters of open channel flow,round glass beads with different diameter produced three closer oughen the bed surface,based on a smooth bed surface and turbulent flow in open channel with bed surface roughness elements of PIV flow field test data,and roughness is discussed after the structure and characteristics of turbulence characteristics of flo w,obtained the following main research results:(1)The theoretical bed surface position is determined,which is located at 0.15 d below the top of the particle.The longitudinal average velocity of smooth bed surface is larger than the longitudinal average velocity of rough bed surface,and the larger the coarse size,the smaller the longitudinal average velocity and the same law of vertical velocity.The longitudinal velocity is distributed as a parabola in relative depth.(2)Fluctuating velocity of the probability density distribution is normal distribution,the bed surface and roughness change near the frequency distribution of the wall fluctuating velocity u,v.With the increase of the roughness Reynolds number Re*,u range decreases,convex peak coefficient F increases gradually,gradually is distribution curve;v presents the opposite trend of change;The surface area of the smooth bed has a clear high and low speed band structure,and the structure of the strip is gradu ally irregular or completely disappeared.(3)The bed surface and roughness of the influence of the vertical turbulence in tensity in general is greater than the vertical,longitudinal and vertical turbulence inten sity after and roughness,area,the change rule of different relative phase flow at the s ame time,the greater the roughness Reynolds number,the greater the vertical turbulence intensity,and the smaller the vertical turbulence intensity;The roughness of the bed surface has the dual effect of restraining the longitudinal turbulent flow and strength ening the vertical turbulent flow in the inner region,while the external flow has the effect of strengthening the vertical and vertical two-way turbulent flow.(4)Reynolds stress,eddy viscosity coefficient and mixing mixing length increas es with the increase of the depth of the water are present to decrease after the law,and roughness after inside and outside the Reynolds stress of absolute value were increased,the area of growth,the increase of Reynolds stress due to the current eddy visc osity coefficient and mixed mixing length decreases,and particle mixed with high frequency and intensity are increased.(5)In different conditions,the relative value of turbulent kinetic energy is obviously different in the inner region.With the increase of water depth ratio,the difference of turbulent kinetic energy is gradually smaller and tends to be the same near the water surface.After roughing,the absolute value of internal turbulent kinetic energy decreases,while the absolute value of external turbulent kinetic energy increases.(6)Q2,Q4 events is a key process of turbulent produce and maintain.Q2,Q4 turbulent events probability increases after adding roughness,high-speed fluid cleaning effect and low speed fluid jet intensifies,particle momentum exchange and energy transfer,the second,four quadrant of the stress and turbulent kinetic energy increase,by increasing the flow of water,energy consumption and roughness resistance.