Study On The PTV Technique And 3D Movement Of Particles

Real-time surface velocity field measurement system and three-dimensional particle velocity measurement system are developed. Systematic experimental research on the movement of coarse sediment particles in open-channel flows was carried out using developed system. Advances have been achieved in the development of velocity measurement approach and the research on the characteristics of particle movement. The results have great value in both theoretic research and practical application of River Dynamics.With multi-CCD and multi-computer system, video and sampling synchronization technique in LAN adopted, real-time measurement of large-scale flow field was achieved. Velocity distribution of the flow field with an area larger than 1000 m2 can be measured in 20 seconds. Successive-frame particle match approach was implemented to ensure high measurement precision. The mixed usage of the successive-sampling and the loop-back-sampling approaches ensures high precision when measuring complicated flows consecutively in real time. A patent has been applied for based on these widely used innovations.A 3D particle velocity measurement system was built upon calibration method of multi-layer regular grid and particle space coordinates determination method of iterative approaching developed in this paper.The distribution of stream-wise particle velocity follows the log-law under various flow conditions and for different particle diameters, and the fluctuation of the other two velocity components is random. The vertical distribution of particle concentration fits Rouse's equation well with > 1.The turbulence intensity of particle velocity decreases when particle size or Re increases and increases with the increase of Fr. The turbulence intensity is the result of space variation and temporal variation of particle velocity.The probability density distribution of the particle velocity fluctuation differs in different flow regions, and is approximately normally distributed where the space restrictions are small. Velocity fluctuation of particles with different sizes is similar.In the bed load layer, the stream-wise particle velocity profile follows the log-law, and the average is 8.2u*. The vertical distribution of particle concentration is nearlylinear, and the concentration at the bottom is 3 times larger than that at the top, which indicates that Ca , the reference concentration of suspended particles in Einstein's equation, is larger.The shear stress of particles is about 5% of the turbulent shear stress of the water. The local energy dissipation of particles caused by the resistance decreases linearly with the increase of the height in the bottom flow region.Though preliminary, these results on three-dimensional movement of particles are novel, and there is no similar systematic research published.