Reynolds number dependence of the small-scale structure of grid turbulence

The small-scale structure of grid turbulence is studied primarily using dat a obtained with a transverse vorticity (omega(3)) probe for values of the T aylor-microscale Reynolds number R-lambda in the range 27-100. The measured spectra of the transverse vorticity component agree within +/-10% with tho se calculated using the isotropic relation over nearly all wavenumbers. Sca ling-range exponents of transverse velocity increments are appreciably smal ler than exponents of longitudinal velocity increments. Only a small fracti on of this difference can be attributed to the difference in intermittency between the locally averaged energy dissipation rate and enstrophy fluctuat ions. The anisotropy of turbulence structures in the scaling range, which r eflects the small values of R-lambda, is more likely to account for most of the difference. All four fourth-order rotational invariants I-alpha (alpha = 1 to 4) proposed by Siggia (1981) were evaluated. For any particular val ue of alpha, the magnitude of the ratio I-alpha/I-1 is approximately consta nt, independently of R-lambda. The implication is that the invariants are i nterdependent, at least in isotropic and quasi-Gaussian turbulence, so that only one power-law exponent may be sufficient to describe the R-lambda dep endence of all fourth-order velocity derivative moments in this type of flo w. This contrasts with previous suggestions that at least two power-law exp onents are needed, one for the rate of strain and the other for vorticity.