Equations relating structure functions of all orders

Abstract

The hierarchy of exact equations is given that relates two-spatial-point velocity structure functions of arbitrary order with other statistics. Because no assumption is used, the exact statistical equations can apply to any flow for which the Navier-Stokes equations are accurate, and they apply no matter how small the number of samples in the ensemble. The exact statistical equations can be used to verify DNS computations and to detect their limitations. For example,if DNS data are used to evaluate the exact statistical equations, then the equations should balance to within numerical precision, otherwise a computational problem is indicated. The equations allow quantification of the approach to local homogeneity and to local isotropy. Testing the balance of the equations allows detection of scaling ranges for quantification of scaling-range exponents. The second-order equations lead to Kolmogorov's equation. All higher-order equations contain a statistic composed of one factor of the two-point difference of the pressure gradient multiplied by factors of velocity difference. Investigation of this pressure-gradient-difference statistic can reveal much about two issues: 1) whether or not different components of the velocity structure function of given order have differing exponents in the inertial range, and 2) the increasing deviation of those exponents from Kolmogorov scaling as the order increases. Full disclosure of the mathematical methods is in xxx.lanl.gov/list/physics.flu-dyn/0102055.