Study On Response Relationship Between Different Bed Forms And Flow Structure

Because of the complexity of turbulent flow,the study of turbulent flow structure under different forms is more complicated.In the nature and engineering,the bed forms is uneven,therefore,the study of the relationship between the bed forms and the flow structure is of practical significance.Due to the rapid development of electronic industry technology,not only in numerical simulation but also in high precision measurement of test instruments,great progress has been made in the research of turbulent flow structure in open channel.On the basis of previous studies,the research on the characteristics of open channel turbulence flow is not only helpful to better understand the characteristics of open channel turbulence flow,but also to provide a reference data for numerical simulation of turbulent flow.It is of practical significance to perfect the basic theory of turbulence.In this paper,the influence of different relative roughness and spherical rough element on the flow structure is tested in a flume.Firstly,the reliability of the popular high-resolution PIV system is validated before the test.Then the related experiments are carried out on the research in this paper.A large number of measured data have been calculated,and the method of statistical analysis is adopted.Some important parameters,such as turbulence intensity and Reynolds stress,are obtained by using the relevant knowledge of viscous fluid mechanics.The main results are as follows:1)In the reliability verification test of PIV system,the analysis and measurement data are compared with the classical theory.On the one hand,the Reynolds stress calculated by the PIV system and the DNS data of the channel flow are highly fitted,on the other hand,the fully developed turbulent zone and the logarithmic law formula in the inner region of the velocity profile are fitted well.The longitudinal and vertical turbulence intensity shows the suppression of vertical turbulent energy by the free surface of open channel flow.Near the free water surface,the vertical turbulence intensity of different boundary conditions is obviously larger than that of the channel flow,whereas the vertical turbulence intensity is opposite,and the free surface dampens the vertical turbulence intensity.The vertical turbulence intensity is transformed to the longitudinal turbulence intensity,so the Reynolds stress measured by the PIV-system and the DNS data of the channel flow are fitted very well,which indicates that the measurement area is not affected by the secondary flow.It can be seen as a quasi-two-dimensional flow.2)In the study of rough wall with 10 mm particle size,according to different relative roughness,the influence of different relative roughness on water flow distribution is analyzed.The average velocity and turbulence intensity of water flow are statistically analyzed,and the difference between velocity distribution and smooth wall velocity formula under different relative roughness is obtained.The roughness function of this paper fits well with the formula put forward by predecessors.The contribution of Reynolds stress near the wall to the burst event is analyzed by using the quadrant method,and the probability of Q2 and Q4 event pairs on different zonal structures of water flow is compared at different two points on the same line.The results show that the phenomenon of near wall cleaning is more frequent than that of jet.(3)After adding spherical rough element with particle size of 50 mm on the bed surface,the spatio-temporal variability of the flow structure from the far region of the spherical rough unit to the nearby frictional velocity increases and then decreases,which is explained by the variation of the shape friction force in this paper.Based on the experiments of the sphere with different flow rates and different water depths,the characteristics of the vortex-structure in the wake region of the sphere are compared with those in the time-averaged flow field.The results show that the flow around the sphere is an unsteady motion process.The instantaneous flow field should be considered in practical engineering calculation.