| Tomographic particle image velocimetry (Tomo-PIV) is a new developed techniquefor three-component three-dimensional (3C-3D) velocity measurement based on thetomographic reconstruction of a volume light intensity field from multiple two-dimensional projections. Nowadays, lots of research on tomographic particle imagevelocimetry has been done, but in our country, none of research has been given a reportabout it.Firstly，A simplification of3D tomographic reconstruction model, which reducedfrom a3D volume with2D images to a2D slice with1D lines, make this3Dreconstruction simplify into a problem of2D plane reconstruction by means of opticaltomography, is applied in this paper. The principles and details of the tomographicalgorithm are discussed, as well as a more detailed look at ART and MART, two of themost well-known algebraic reconstruction techniques. The study of ART and MARTreconstruction algorithm is carried out by means of computer-simulated imagereconstruction procedure. The character of ART and MART is present from differentsides. By pre-processing the initial particle image, the reconstruction of particle imagehas been greatly improved. Furthermore, a calculation of effect of particle density andnumber of cameras on reconstruction is made. At last, the three-dimensional volumeparticle field is reconstructed by this means of optical tomography.Secondly，verify and assess the performance of the tomographic particle imagevelocimetry with the experiment measured by the2D plane particle image velocimetry.The tomographic particle image velocimetry achieve the measurement of flow fieldwith a result of3D-3C velocity which could be taken on research about the threedimension characteristics of turbulence. Compare the averaged velocity field betweenthe2D particle image velocimetry and the3D tomographic particle image velocimetry,it could be found in the Logarithmic region, the velocity field measured by tomographicparticle image velocimetry agrees with the expected performance.Finally, the experiment data of turbulent boundary layers which was measured bytomographic particle image velocimetry. Research on the large scale structure in theLogarithmic region of the tomographic experiment data is done in this paper. Two-pointcorrelations based on streamwise velocity fluctuations indicates that the coherentstructure is stretched in streamwise directions, More near to the wall it stretch stronger.It might relate to the upstream elongation of low-momentum fluid in time due to newdevelopments of hairpin-like vortices. length in streamwise and wall-normalwise of coherrent structures gets bigger while the inclining angle gets smaller, and away fromthe wall. variation of the streamwise integral length scales across different wall-normalheights indicates that the integral length scale depicts an increasing trend within the logregion, reaching a maximum at y=0.27δ then decreases beyond this wall-normallocation, While the spanwise integral length scales is increased on wall-normaldirection. the3D space–time correlation of coherent structures is computed andansysied, its rate of migration velocity is0.4m/s which is different with the local meanvelocity. In addition, in velocity probability statistical analysis, a drum is found at0.35m/s in the PDF of velocity u which indicate a the vortex structure embedded in lowmomentum take a strong impact on this. |
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