Hydrogen Bubble Digital Particle Image Velocimetry

Digital Particle Image Velocimetry is the developing full flow field measurement method .In this paper, we mainly study the key technique in this method-the matching algorithm of particle image.The calculation formula of DPIV technique is the originate definition of velocity: V=[S(t2)-S(tl)]/(t2-tl).On the two neighboring frame of images , we search the two small areas which have the largest correlation ,then divide their distance by their shooting interval, thus we got the average velocity of this small area in this interval. The main calculation in the particle image matching algorithm is to have the two visual seriate images taken the cross-correlation arithmetic based on the fast fourier transform. This paper discusses the basic principle of the cross-correlation arithmetic in detail, discuss each stage of its produce and development and also discuss the thinking, the merit and the defect of each algorithm. On the base of all these discussing, we confirm our algorithm and realize it in programming with C++.We describe the international development and research state of DPIV technique, and discuss the selection of particle and the usage of light sheet in particular. Because the price of the hardware of the DPIV technique is very high, we develop a DPIV technique by using hydrogen bubble as trace particle. We investigate the whole process and technique details of hydrogen bubble DPIV technique, such as the optimum condition of producing hydrogen bubble, the design of the strong optical light sheet, the software interface of the image acquisition, the software interface, analysis of the specification parameters of the DPIV technique and the selection of the key laboratory parameters.We adopt the DPIV test equipment using hydrogen bubble as trace particle developed by ourselves to measure the typical flow of column circuitous, plot the test result in flow field figure graph, give the explanation in fluid mechanics .We compare it with the expressed field graph and numerical simulation of column circuitous and prove the practicability, economy andfeasibility of the particle image velocimetry.It shows that the DPIV software composing with the image acquisition, image processing, image matching, plotting test result in field has got a satisfactory result. It has active meaning in the spread and handle of DPIV technique in our country.In this research, we use the locomotive axis transform method in the DPIV image processing in a creative way .We show the vortex sightless originally on the transformed reference axis clearly, got the Karman vortex street which can only be taken by camera movement anciently .We use computer simulation further to prove the correctness of this method. We make the cause and mechanism that vortex on the background flow affects the particle shooting clear. It has reference worthiness on this kind of research in the future.