On the Kolmogorov Constants for the Second-Order Structure Function and the Energy Spectrum

Abstract

We examine the behavior of the Kolmogorov constants C_2, C_k, and C_{k1}, which are, respectively, the prefactors of the second order longitudinal structure function, the three dimensional and one-dimensional longitudinal energy spectrum in the inertial range. We show that their ratios, C_2/C_{k1} and C_k/C_{k1}, exhibit clear dependence on the micro-scale Reynolds number R_λ, implying that they cannot all be independent of R_λ. In particular, it is found that (C_{k1}/C_2-0.25) = 1.95R_λ^{-0.68}. The study further reveals that the widely-used relation C_2 = 4.02 C_{k1} holds only asymptotically when R_λ <= 10^5. It is also found that C_2 has much stronger R_λ-dependence than either C_k, or C_{k1} if the latter indeed has a systematic dependence on R_λ. We further show that the variable dependence on R_λ of these three numbers can be attributed to the difference of the inertial range in real- and wavenumber-space, with inertial range in real-space known to be much shorter than that in wavenumber space.

10 pages, 4 figures. Journal of Fluid Mechanics format (JFM.cls)