Using direct numerical simulations (DNS) and large-eddy simulations (LES) of velocity and passive scalar in isotropic turbulence (up to 512 3 grid points), we examine directly and quantitatively the refined similarity hypotheses as applied to passive scalar fields (RSHP) with Prandtl number of order one. Unlike previous experimental investigations, exact energy and scalar dissipation rates were used and scaling exponents were quantified as a function of local Reynolds number. We first

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... e that the forced DNS and LES scalar fields exhibit realistic inertial-range dynamics and that the statistical characteristics compare well with other numerical, theoretical and experimental studies. The Obukhov-Corrsin constant for the k −5/3 scalar variance spectrum obtained from the 512 3 mesh is 0.87 ± 0.10. Various statistics indicated that the scalar field is more intermittent than the velocity field. The joint probability distribution of locally-averaged energy dissipation r and scalar dissipation χ r is close to log-normal with a correlation coefficient of 0.25 ± 0.01 between the logarithmic dissipations in the inertial subrange. The intermittency parameter for scalar dissipation is estimated to be in the range 0.43 ∼ 0.77, based on direct calculations of the variance of ln χ r . The scaling exponents of the conditional scalar increment δ r θ| χ r , r suggest a tendency to follow RSHP. Most significantly, the scaling exponent of δ r θ| χ r , r over r was shown to be approximately − 1 6 in the inertial subrange, confirming a dynamical aspect of RSHP. In agreement with recent experimental results (Zhu et al. 1995; Stolovitzky et al. 1995) , the probability distributions of the random variable β s = δ r θ| χ r , r /(χ 1/2 r −1/6 r r 1/3 ) were found to be nearly Gaussian. However, contrary to the experimental results, we find that the moments of β s are almost identical to those for the velocity field found in Part 1 of this study (Wang et al. 1996) and are insensitive to Reynolds number, large-scale forcing, and subgrid modelling.