  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 $V_T = \Delta v(r)/(r\epsilon_r)^{1/3}$, where $\Delta
u(r)$ and $\Delta v(r)$ 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 parameterised by a suitably defined local Reynolds number, providing the
first conclusive experimental evidence in support of the first refined
similarity hypothesis and its universality.
