TitleA study of the fine-scale three-dimensional flow structures in turbulence using time-resolved stereoscopic scanning particle image velocimetry
NameCheng, Ye (author), Diez, Francisco Javier (chair), Jaluria, Yogesh (internal member), Knight, Doyle (internal member), Guo, Qizhong (outside member), Rutgers University, Graduate School - New Brunswick,
SubjectMechanical and Aerospace Engineering,
DescriptionA time-resolved stereoscopic scanning particle image velocimetry (TR-SSPIV) system was developed to investigate the fine-scale 3D structures in free shear turbulent jets. The system provided a simultaneous measurement of the three-component velocity field in a three-dimensional volume (3D3C) with Kolmogorov-scale (eta) resolution, providing a true representation of the complete nine-component velocity gradient tensor. Quantitative visualization of the coherent structures at fine-scale turbulence is obtained and four basic structural shapes (sheets, tube, square ribbons and spherical blobs) are identified as building blocks of complex turbulent structures. The measurement volume had dimensions of 43eta x 20eta x 18eta, which allowed isolating individual structures. These rendered shapes had dimensions that range from 1.5-5eta to 20-30eta. The local acceleration du/dt is obtained and represented as 3D structures. These showed a strong anti-alignment with the convective acceleration term, which helps validate experimentally the Random Taylor Hypothesis. A novel vortex identification scheme is also introduced based on the local pressure. The method is compared to other published ones including enstrophy, Q, Lambda2 and Delta criteria. Four different flow configurations are tested and extensive statistical analyses are performed to study the probability density function (PDF), joint PDF, and spectra of the velocity gradients. The analysis also considered the vorticity, rate of strain, enstrophy, and dynamic parameters such as enstrophy production rate and energy dissipation rate. Accuracy assessments included result comparison to isotropy theory and evaluation of the local conservation of mass. The flow statistics and scaling of turbulence at fine scales are compared extensively to published theoretical, numerical, and experimental results.
NoteIncludes bibliographical references
Noteby Ye Cheng
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.