Direct assessment of Kolmogorov's first refined similarity hypothesis

Using volumetric velocity data from a turbulent laboratory water flow and numerical simulations of homogeneous, isotropic turbulence, we present a direct experimental and numerical assessment of Kolmogorov's first refined similarity hypothesis based on three-dimensional measurements of the local energy dissipation rate epsilon(r) measured at dissipative scales r. We focus on the properties of the stochastic variables V-L = Delta u(r)/(r epsilon(r))(1/3) and V-T = Delta u(r)/(r epsilon(r))(1/3), where Delta u(r) and Delta u(r) are longitudinal and transverse velocity increments. Over one order of magnitude of scales r within the dissipative range, the distributions of V-L and V-T from both experiment and simulation collapse when parametrized by a suitably defined local Reynolds number, providing conclusive experimental evidence in support of the first refined similarity hypothesis and its universality