Measurement of rotation and strain-rate tensors by using stereoscopic PIV

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A simple technique is described for measuring the mean rate-of-displacement (velocity gradient) tensor in a plane by using a conventional stereoscopic PIV system. The technique involves taking PIV data in two or three closely-spaced parallel planes at different times. All components of the mean rate-of-displacement tensor are then calculated by using finite difference formulas. Planar measurements of the mean vorticity vector, rate-of-rotation and rate-of-strain tensors and the production of turbulent kinetic energy can be accomplished. Parameters of the Q-criterion and negative-λ_2 techniques used for vortex identification can be evaluated in the mean flow field. Dissipation rate of the turbulent kinetic energy in a non-isotropic three-dimensional flow field may also be estimated. Experimental data obtained for a round turbulent jet normal to a crossflow in a low-speed wind tunnel are presented to show the applicability of the proposed technique. The PIV cameras and light sheet optics shown in Fig. 1a are mounted on the same traverse mechanism in order to displace the measurement plane accurately. Data obtained in constant-y and -z planes are presented. Fig. 1b shows a contour plot of the normalized production rate of turbulent kinetic energy P*=PD/U3 in the z/D=2 plane (D is the jet diameter, U is the crossflow velocity). P* is evaluated by using its exact definition, i.e., all nine additive terms in the definition are included. Smoothness of the contour plot indicates the successful implementation of the technique. Measurement uncertainties are discussed and algebraic relations for uncertainties in P and the parameter of the Q-criterion are presented. Consistency of the measurements is verified by showing agreement of two data sets obtained in two perpendicular planes. Accuracy of the data can be improved if optimal spacing between velocity vectors is employed. The feasibility of measuring the truncation error in the rotation- and strain-rate tensors is also demonstrated.
Original languageEnglish
Title of host publicationProceedings of 12th International Symposium on Application of Laser Techniques to Fluid Mechanics
VolumeBook of Abstract, CD-ROM with papers, papers on website, paper 18.4 (12 pages)
Place of PublicationLisbon
PublisherInstituto Superior Técnico
Publication date2004
Publication statusPublished - 2004
Event12th International Symposium on Application of Laser Techniques to Fluid Mechanics - Lisbon, Portugal
Duration: 12 Jul 200415 Jul 2004


Conference12th International Symposium on Application of Laser Techniques to Fluid Mechanics
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