A new method to describe small scale statistical information from passive scalar fields has been
proposed by Wang and Peters (2006). They used direct numerical simulations (DNS) of homogeneous shear
flow to introduce the innovative concept. This novel method determines the local minimum and maximum
points of a fluctuating scalar field via gradient trajectories starting from every grid point in the direction of
the steepest ascending and descending scalar gradients. Relying on gradient trajectories, a dissipation element
is defined as the region of all the grid points the trajectories of which share the same pair of maximum
and minimum points. The procedure has also been successfully applied to various DNS fields of homogeneous
shear turbulence using the three velocity components and the kinetic energy as scalar fields. To validate
statistical properties of these elements derived from DNS (Wang and Peters 2006, 2008), dissipation elements
are for the first time determined based on experimental data of a fully developed turbulent channel
flow. The dissipation elements are deduced from the gradients of the instantaneous fluctuation of the three
velocity components u5, v5, and w5 and the instantaneous kinetic energy k5, respectively. The required 3D velocity
data is obtained investigating a 17.82 × 17.82 × 2.7 mm3 (0.356 × 0.356 × 0.054 ) test volume
using tomographic particle-image velocimetry (Tomo-PIV). The measurements are conducted at a Reynolds
number of 1.7× 104 based on the channel half-height and the bulk velocity U. Detection and analysis of
dissipation elements from the experimental velocity data are presented. The statistical results are compared
to the DNS data from Wang and Peters (2006, 2008). 德国LaVision PIV/PLIF粒子成像测速场仪
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