arXiv subjects

Daigen Fukayama

Publications and source records attributed to Daigen Fukayama.

3 recordsLinked to original sources

arXiv2001

Local properties of extended self-similarity in 3D turbulence

Using a generalization of extended self-similarity we have studied local scaling properties of 3D turbulence in a direct numerical simulation. We have found that these properties are consistent with lognormal-like behavior of energy dissipation fluctuations with moderate amplitudes for space scales $r$ beginning from Kolmogorov length $η$ up to the largest scales, and in the whole range of the Reynolds numbers: $50 \leq R_λ \leq 459$. The locally determined intermittency exponent $μ(r)$ varies with $r$; it has a maximum at scale $r=14 η$, independent of $R_λ$.

nlin.CD↗

arXiv2000

Pressure spectrum and structure function in homogeneous turbulence

The pressure spectrum and structure function in homogeneous steady turbulence of an incompressible fluid is studied using direct numerical simulation. The resolution of the simulation is up to $1024^3$ and the Taylor microscale Reynolds number $\Rl$ is between 38 and 478. The energy spectrum is found to have a small but finite inertial range followed by a bump at large wavenumbers. The Kolmogorov constant $K$ is found to be $1.66\pm 0.08$. The pressure spectrum also has a small but finite inertial range of $P(k)=B_p\eb^{4/3}k^{-7/3}$ followed by a bump of nearly $k^{-5/3}$ range at higher wavenumbers. Both scaling ranges match at a crossover wavenumber, $k_p$, which is a characteristic wavenumber for the pressure gradient. The constant $B_p$ is found to be about $8.34\pm 0.15$ for $\Rl=460$. Its non-universality is discussed. The second order pressure structure function, computed in terms of the fourth order velocity structure functions, agrees well with that obtained by the direct measurement over separations ranging between the inertial and dissipation scales.

nlin.CD↗

arXiv2000

Longitudinal Structure Functions in Decaying and Forced Turbulence

In order to reliably compute the longitudinal structure functions in decaying and forced turbulence, local isotropy is examined with the aid of the isotropic expression of the incompressible conditions for the second and third order structure functions. Furthermore, the Karman-Howarth-Kolmogorov relation is investigated to examine the effects of external forcing and temporally decreasing of the second order structure function. On the basis of these investigations, the scaling range and exponents $ζ_n$ of the longitudinal structure functions are determined for decaying and forced turbulence with the aid of the extended-self-similarity (ESS) method. We find that $ζ_n$'s are smaller, for $n \geq 4$, in decaying turbulence than in forced turbulence. The reasons for this discrepancy are discussed. Analysis of the local slopes of the structure functions is used to justify the ESS method.

chao-dyn↗