A new method to describe statistical information from passive scalar fields has been proposed by Wang and Peters The length-scale distribution function of the distance between extremal points in passive scalar turbulence, J. Fluid Mech. 554, 457 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 the 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 L. Wang and N. Peters, Length-scale distribution functions and conditional means for various fields in turbulence, J. Fluid Mech. 608, 113 2008. 德國LaVision PIV/PLIF粒子成像測速場儀 體視層析粒子成像測速系統(tǒng)(Tomo-PIV) 自適應(yīng)粒子成像測速場儀（PIV）