The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Makoto Okamura - One of the best experts on this subject based on the ideXlab platform.
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Modal time correlation functions for homogeneous Isotropic Turbulence in a projection operator method
Physics of Fluids, 2015Co-Authors: Makoto OkamuraAbstract:Applying a projection operator method to homogeneous Isotropic Turbulence in the Lagrangian and Eulerian specifications of the flow field, we obtain a closure equation, which is called the similarity approximation (SA) equation, for the time correlation function. We compare its solutions with the time correlation function obtained from direct numerical simulation in the Eulerian specification and with that obtained from direct interaction approximation in the Lagrangian specification. Results of the comparison show that the SA equation can express time correlation for homogeneous Isotropic Turbulence in the Lagrangian and Eulerian specifications.
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Modal time correlation functions for homogeneous Isotropic Turbulence in a projection operator method
Physics of Fluids, 2015Co-Authors: Makoto OkamuraAbstract:Applying a projection operator method to homogeneous Isotropic Turbulence in the Lagrangian and Eulerian specifications of the flow field, we obtain a closure equation, which is called the similarity approximation (SA) equation, for the time correlation function. We compare its solutions with the time correlation function obtained from direct numerical simulation in the Eulerian specification and with that obtained from direct interaction approximation in the Lagrangian specification. Results of the comparison show that the SA equation can express time correlation for homogeneous Isotropic Turbulence in the Lagrangian and Eulerian specifications.
Iwao Hosokawa - One of the best experts on this subject based on the ideXlab platform.
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Statistical treatment of scalar transfer in Isotropic Turbulence
International Journal of Heat and Mass Transfer, 2004Co-Authors: Iwao HosokawaAbstract:Abstract It has recently been known that local high-gradient regions of an advected scalar, such as temperature or mass contaminant, in a turbulent state of fluid form thin sheets, randomly oriented and moving around with turbulent motion. Here is presented a joint multifractal model for velocity and scalar dissipations in Isotropic Turbulence which can predict the statistical distributions of the worms, vorticity-concentrated regions, as well as the above-described scalar-gradient sheets. This model allows us to derive turbulent diffusion coefficient in Isotropic Turbulence scaled by Reynolds number and Prandtl number, which predominates far over molecular diffusion coefficient.
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A Generalization of Refined Similarity Hypothesis for Isotropic Turbulence
Journal of the Physical Society of Japan, 2000Co-Authors: Iwao HosokawaAbstract:The refined similarity hypothesis for Isotropic Turbulence established by Kolmogorov in 1962 is generalized so that the statistics of similarity variable may have a slight scale-ratio dependence. A reasonable form of the dependence is given on the basis of a recent multifractal model of intermittent energy dissipation and on some theoretical and experimental knowledge. This modification leads us to predict reasonable values of all the Kolmogorov prefactors and the scalings of longitudinal as well as transverse velocity structure functions in Isotropic Turbulence.
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Statistics of Lateral Velocity Increment in Isotropic Turbulence
Journal of the Physical Society of Japan, 1996Co-Authors: Iwao Hosokawa, Shin–ichi Oide, Tsukasa Satoh, Kiyoshi YamamotoAbstract:The probability density function of lateral velocity increment across an arbitrary distance ranging from the Kolmogorov scale to the integral scale in isotropoic Turbulence is predicted in a semi-empirical way. The method is based on the previous theory of the first author for treating statistics of longitudinal velocity increment and new data of direct numerical simulation of decaying Isotropic Turbulence on a 512 3 grid.
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A paradox of the 1D surrogate of dissipation rate in Isotropic Turbulence
Journal of the Physical Society of Japan, 1995Co-Authors: Iwao HosokawaAbstract:It is pointed out within the framework of Kolmogorov and Obukhov's refined similarity hypothesis that the 1D surrogate of energy dissipation rate in Isotropic Turbulence, which has been conventionally used by many experimentalists to investigate intermittency in Isotropic Turbulence, leads to an unrealistic prediction of the probability density function of velocity gradient. This suggests that any discussion of intermittency of Turbulence based on the 1D surrogate may be of a more or less qualitative nature.
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Probability distribution function of the temperature increment in Isotropic Turbulence.
Physical Review E, 1994Co-Authors: Iwao HosokawaAbstract:The statistics of a temperature increment across a distance in the inertial range in Isotropic Turbulence is discussed on the basis of the Obukhov-Corrsin similarity, the extensive use of the Kolmogorov refined similarity hypothesis and the three-dimensional tetranomial Cantor set model for Isotropic Turbulence with a passive advected scalar. The result compares well with available experimental data.
Xing Zhang - One of the best experts on this subject based on the ideXlab platform.
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Temporal decorrelations in compressible Isotropic Turbulence
Physical review. E Statistical nonlinear and soft matter physics, 2013Co-Authors: Xing ZhangAbstract:Temporal decorrelations in compressible Isotropic Turbulence are studied using the space-time correlation theory and direct numerical simulation. A swept-wave model is developed for dilatational components, while the classic random sweeping model is proposed for solenoidal components. The swept-wave model shows that the temporal decorrelations in dilatational fluctuations are dominated by two physical processes: random sweeping and wave propagation. These models are supported by the direct numerical simulation of compressible Isotropic Turbulence, in the sense that all curves of normalized time correlations for different wave numbers collapse into a single one using the normalized time separations. The swept-wave model is further extended to account for a constant mean velocity.
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Time Correlations Of Pressure In Isotropic Turbulence
Physics of Fluids, 2008Co-Authors: Huadong Yao, Meng Wang, Xing ZhangAbstract:The time correlations of pressure modes in stationary Isotropic Turbulence are investigated under the Kraichnan and Tennekes “random sweeping” hypothesis. A simple model is obtained which predicts a universal form for the time correlations. It implies that the decorrelation process of pressure fluctuations in time is mainly dominated by the sweeping velocity, and the pressure correlations have the same decorrelation time scales as the velocity correlations. These results are verified using direct numerical simulations of Isotropic Turbulence at two moderate Reynolds numbers; the mode correlations collapse to the universal form when the time separations are scaled by wavenumber times the sweeping velocity, and the ratios of the correlation coefficients of pressure modes to those of velocity modes are approximately unity for the entire range of time separation.
P K Yeung - One of the best experts on this subject based on the ideXlab platform.
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Reynolds number scaling of velocity increments in Isotropic Turbulence.
Physical review. E, 2017Co-Authors: Kartik P Iyer, Katepalli R. Sreenivasan, P K YeungAbstract:Using the largest database of Isotropic Turbulence available to date, generated by the direct numerical simulation (DNS) of the Navier-Stokes equations on an 8192^{3} periodic box, we show that the longitudinal and transverse velocity increments scale identically in the inertial range. By examining the DNS data at several Reynolds numbers, we infer that the contradictory results of the past on the inertial-range universality are artifacts of low Reynolds number and residual anisotropy. We further show that both longitudinal and transverse velocity increments scale on locally averaged dissipation rate, just as postulated by Kolmogorov's refined similarity hypothesis, and that, in Isotropic Turbulence, a single independent scaling adequately describes fluid Turbulence in the inertial range.
Changhoon Lee - One of the best experts on this subject based on the ideXlab platform.
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source of acceleration intermittency in Isotropic Turbulence
Journal of Mechanical Science and Technology, 2012Co-Authors: Changhoon Lee, Yongnam Park, Jaedal JungAbstract:Strong acceleration intermittency in fluid Turbulence is interpreted in the context of different supports for local enstrophy and dissipation by introducing a new decomposition of acceleration. This paper proposes a simple Lamb Vortex Model that captures statistical features of acceleration, such as probability density functions, flatness factors, and correlation coefficients, observed in the direct numerical simulation of homogeneous Isotropic Turbulence.
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Decaying versus stationary Turbulence in particle-laden Isotropic Turbulence: Turbulence modulation mechanism
Physics of Fluids, 2012Co-Authors: Abouelmagd Abdelsamie, Changhoon LeeAbstract:The objective of the current paper is to clarify the physical distinction between Turbulence modulations by laden particles in decaying Isotropic Turbulence and stationary Isotropic Turbulence. Direct numerical simulations of stationary and decaying Isotropic Turbulence were carried out using 1283 grid points at a Taylor micro-scale Reynolds number of Rλ ∼ 70. The effect of O(106) solid particles with a different Stokes number (St) was implemented as a point-force approximation in the Navier-Stokes equation. Turbulent kinetic energy, acceleration, enstrophy, strain rate, and various spectra were examined to determine the distinctions. Turbulence modulation in decaying Turbulence is qualitatively and quantitatively inconsistent compared to that in stationary Turbulence, particularly when the particles have St ≤ 1, mainly due to the artificial forcing necessary for stationary status. For the particles with St > 1, however, decaying and stationary Turbulence are qualitatively similar. A simple analysis confi...
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Intermittency of acceleration in Isotropic Turbulence
Physical Review E - Statistical Nonlinear and Soft Matter Physics, 2005Co-Authors: Sang Lee, Changhoon LeeAbstract:The intermittency of acceleration is investigated for Isotropic Turbulence using direct numerical simulation. Intermittently found acceleration of large magnitude always points towards the rotational axis of a vortex filament, indicating that the intermittency of acceleration is associated with the rotational motion of the vortices that causes centripetal acceleration, which is consistent with the reported result for the near-wall Turbulence. Furthermore, investigation on movements of such vortex filaments provides some insights into the dynamics of local dissipation, enstrophy and acceleration. Strong dissipation partially covering the edge of a vortex filament shows weak correlation with enstrophy, while it is strongly correlated with acceleration.
