Turbulence of the round jet has been assessed using invariants
of the velocity gradient tensor. Experimental data, obtained
using Tomographic Particle Image Velocimetry (Tomo-PIV),
using four PCO-4000 cameras with 11 megapixel resolution,
is presented for a seeded free air jet, operating in the turbulent
regime and the Re number based on the diameter of the nozzle
is 10000. Using the acquired 3-D velocity fields, the local
statistical and geometrical structure of three-dimensional
turbulent flow can be described by properties of the velocity
gradient tensor. The invariants of the velocity gradient (R and
Q), rate-of-strain ( Rs andQs ), and rate-of-rotation (Qw )
tensors are analyzed across the turbulent expanding regions at
different distances from the nozzle outlet. More specifically,
the JPDF of invariants is computed, which allows a detailed
statistical characterization of the dynamics, geometry and
topology of the flow during the entrainment process. It 首ld
be noted that the results obtained are indicative of the
preliminary work in this area. 自适应粒子成像测速场仪（PIV） 德国LaVision PIV/PLIF粒子成像测速场仪 体视层析粒子成像测速系统(Tomo-PIV)
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