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Conditional statistics of homogeneous isotropic turbulent flow isinvestigated by means of high-Reynolds number direct numerical simulationsperformed with $2048^3$ collocation points. Eulerian as well as Lagrangianvelocity increment statistics under several conditions are analyzed andcompared. In agreement with experimental data longitudinal probability densityfunctions $P(\delta^{||}_l u|\epsilon_l)$ conditioned on a scale-averagedenergy dissipation rate are close to Gaussian distributions over all scaleswithin the inertial range of scales. Also transverse increments conditioned oneither the dissipation rate or the square of the vorticity have quasi-Gaussianprobability distribution functions (PDFs). Concerning Lagrangian statistics wefound that conditioning on a trajectory averaged energy-dissipation rate$\epsilon_\tau$ significantly reduces the scale dependence of the incrementPDFs $P(\delta_\tau u_i|\epsilon_\tau)$. By means of dimensional arguments wepropose a novel condition for Lagrangian increments which is shown to reduceeven more the flatness of the corresponding PDFs and thus intermittency in theinertial range of scales. The conditioned Lagrangian PDF corresponding to thesmallest increment considered is reasonably well described by theK41-prediction of the PDF of acceleration. Conditioned structure functions showapproximately K41-scaling with a larger scaling range than the unconditionedones.

Conditional Eulerian and Lagrangian velocity increment statistics of fully developed turbulent flow