Research On Measurement Method Of Three-dimensional Flow Field Downstream Of Single-bend Base On PIV

Particle image velocimetry(PIV) is a new flow measurement technique, it is developed based on traditional flow visualization technique and the use of image processing technology. PIV overcome the shortcomings of single-point measurement technology and can measure the whole flow field quickly and non-intrusive. In addition, PIV is fast response, high accuracy and high spatial resolution, is the most advanced technology for complexity flow measurement. This paper aims to study the specific use of PIV devices and the impact of key parameters on the measurement results. And this paper also proposes an ingenious method for three-dimensional reconstruction based on the two-dimensional images. In order to achieve the accurate measurement for complex flow field by PIV, the main work completed as follows:(1) The working principle of the PIV device as well as the composition of PIV system developed by Beijing Cube World Technology are described in this paper, and carry out the design and analysis of the entire experimental system.(2) The experiments are conducted for the flow field reproduction of the round straight pipe flow field after fully developed by PIV devices, and compared with the velocity distribution of pipelines cross flow velocity calculated by Nikuradse' velocity distribution formulas. The impact of key parameters for experimental results are analyzed through the changing of key parameters in PIV experiments. The method to calculate the cross-frame time in different rates are also proposed in this paper, which is tested by experiments and the measurement error decreased 31.8%. And the optimum combination of the key parameters for different flow rates are obtained.(3) The method for three-dimensional reconstruction is proposed based on the two-dimensional images obtained by PIV experimental, and the feasibility of this method is verified through the reproduced of three-dimensional velocity flow field in the pipe which is fully development. The results show that the three-dimensional velocity flow field obtained by this method is same with the theory, and compared the results of three interpolation methods, the cubic spline interpolation is more suitable.(4) The research in the complex flow field downstream of a single elbow is carried out combined with the method of three-dimensional reconstruction. And the features of single bend downstream flow field are analyzed and compared with computational fluid dynamics(CFD) simulation method. The results show that the interval of two-dimensional plane is shoot as much as possible for the measurement of complex flow field, and the experimental results will be optimized and more accurate.