在充分发展的湍动槽流中采用层析粒子成像测速技术来测量耗散元素

2011/02/24   下载量： 3 次

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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).

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