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ISSN オンライン: 2642-0554

DUAL-PLANE STEREO PIV (DSPIV) MEASUREMENTS OF THE VELOCITY GRADIENT TENSOR FIELD AT THE SMALL SCALES OF TURBULENT FLOWS

John A. Mullin
Laboratory for Turbulence & Combustion (LTC) Department of Aerospace Engineering The University of Michigan Ann Arbor, Ml 48109-2140 USA

Werner J. A. Dahm
School for Engineering of Matter, Transport, and Energy Arizona State University Tempe, AZ, 85287, USA

要約

We present results from the first direct nonintrusive fully-resolved simultaneous measurements of the complete nine-component velocity gradient tensor field ∇u(x,t) in a turbulent shear flow. The measurement technique involves a unique frequency-based dual-plane stereo PIV system that provides all three velocity components ui(x,t) in two differentially-spaced measurement planes formed by two pairs of double-pulsed light sheets, in this case at 532 nm and 635 nm. Tests using synthetic PIV, single-plane imaging and coincident-plane imaging allow assessments of the accuracy of such measurements. Direct differentiation of velocity components within each plane and between planes provides the full ∇u(x,t) field in a plane, and thus the instantaneous spatial structure and statistics of gradient fields such as the true vorticity vector field ω(x,t), the full strain rate tensor field ε(x,t), and the true kinetic energy dissipation rate field 2υ ε:ε(x,t). Present results characterize the accuracy of these measurements, and provide initial examples of the resulting structure, statistics, and scalings of such gradient fields in turbulent shear flows.