The Experts below are selected from a list of 16251 Experts worldwide ranked by ideXlab platform
P K Yeung - One of the best experts on this subject based on the ideXlab platform.
-
gpu acceleration of a petascale application for turbulent mixing at high Schmidt Number using openmp 4 5
Computer Physics Communications, 2018Co-Authors: M P Clay, Dhawal Buaria, P K Yeung, Toshiyuki GotohAbstract:Abstract This paper reports on the successful implementation of a massively parallel GPU-accelerated algorithm for the direct numerical simulation of turbulent mixing at high Schmidt Number. The work stems from a recent development (Comput. Phys. Commun., vol. 219, 2017, 313–328), in which a low-communication algorithm was shown to attain high degrees of scalability on the Cray XE6 architecture when overlapping communication and computation via dedicated communication threads. An even higher level of performance has now been achieved using OpenMP 4.5 on the Cray XK7 architecture, where on each node the 16 integer cores of an AMD Interlagos processor share a single Nvidia K20X GPU accelerator. In the new algorithm, data movements are minimized by performing virtually all of the intensive scalar field computations in the form of combined compact finite difference (CCD) operations on the GPUs. A memory layout in departure from usual practices is found to provide much better performance for a specific kernel required to apply the CCD scheme. Asynchronous execution enabled by adding the OpenMP 4.5 NOWAIT clause to TARGET constructs improves scalability when used to overlap computation on the GPUs with computation and communication on the CPUs. On the 27-petaflops supercomputer Titan at Oak Ridge National Laboratory, USA, a GPU-to-CPU speedup factor of approximately 5 is consistently observed at the largest problem size of 819 2 3 grid points for the scalar field computed with 8192 XK7 nodes.
-
the turbulent Schmidt Number
Journal of Fluids Engineering-transactions of The Asme, 2014Co-Authors: Diego Donzis, P K Yeung, Konduri Aditya, K R SreenivasanAbstract:We analyze a large database generated from recent direct numerical simulations (DNS) of passive scalars sustained by a homogeneous mean gradient and mixed by homogeneous and isotropic turbulence on grid resolutions of up to 40963 and extract the turbulent Schmidt Number over large parameter ranges: the Taylor microscale Reynolds Number between 8 and 650 and the molecular Schmidt Number between 1/2048 and 1024. While the turbulent Schmidt Number shows considerable scatter with respect to the Reynolds and molecular Schmidt Numbers separately, it exhibits a sensibly unique functional dependence with respect to the molecular Peclet Number. The observed functional dependence is motivated by a scaling argument that is standard in the phenomenology of three-dimensional turbulence.
-
direct numerical simulation of turbulent mixing at very low Schmidt Number with a uniform mean gradient
Physics of Fluids, 2014Co-Authors: P K Yeung, K R SreenivasanAbstract:In a recent direct numerical simulation (DNS) study [P. K. Yeung and K. R. Sreenivasan, “Spectrum of passive scalars of high molecular diffusivity in turbulent mixing,” J. Fluid Mech. 716, R14 (2013)] with Schmidt Number as low as 1/2048, we verified the essential physical content of the theory of Batchelor, Howells, and Townsend [“Small-scale variation of convected quantities like temperature in turbulent fluid. 2. The case of large conductivity,” J. Fluid Mech. 5, 134 (1959)] for turbulent passive scalar fields with very strong diffusivity, decaying in the absence of any production mechanism. In particular, we confirmed the existence of the −17/3 power of the scalar spectral density in the so-called inertial-diffusive range. In the present paper, we consider the DNS of the same problem, but in the presence of a uniform mean gradient, which leads to the production of scalar fluctuations at (primarily) the large scales. For the parameters of the simulations, the presence of the mean gradient alters the ph...
-
high Schmidt Number scalars in turbulence structure functions and lagrangian theory
Physics of Fluids, 2004Co-Authors: Michael S Borgas, Diego Donzis, B L Sawford, P K YeungAbstract:We demonstrate the existence of Batchelor’s viscous-convective subrange using direct numerical simulation (DNS) results to confirm the logarithmic dependence of the scalar structure function on the separation for the scalar field generated by stationary isotropic turbulence acting on a uniform mean scalar gradient. From these data we estimate the Batchelor constant Bθ≈5. By integrating a piecewise continuous representation of the scalar variance spectrum we calculate the steady-state scalar variance as a function of Reynolds Number and Schmidt Number. Comparison with DNS results confirms the Reλ−1 behavior predicted from the spectral integration, but with a coefficient about 60% too small. In the large Reynolds Number limit the data give a value of 2.5 for the mechanical-to-scalar time scale ratio. The dependence of the data for the scalar variance on Schmidt Number agrees very well with the spectral integration using the values of the Batchelor constant estimated from the structure function. We also car...
-
Schmidt Number dependence of derivative moments for quasi static straining motion
Journal of Fluid Mechanics, 2003Co-Authors: Joerg Schumacher, K R Sreenivasan, P K YeungAbstract:Bounds on high-order derivative moments of a passive scalar are obtained for large values of the Schmidt Number, $Sc$ . The procedure is based on the approach pioneered by Batchelor for the viscous–convective range. The upper bounds for derivative moments of order $n$ are shown to grow as $Sc^{n/2}$ for very large Schmidt Numbers. The results are consistent with direct numerical simulations of a passive scalar, with $Sc$ from 1/4 to 64, mixed by homogeneous isotropic turbulence. Although the analysis does not provide proper bounds for normalized moments, the combination of analysis and numerical data suggests that they decay with $Sc$ , at least for odd orders.
Satoru Komori - One of the best experts on this subject based on the ideXlab platform.
-
effect of Schmidt Number on mass transfer across a sheared gas liquid interface in a wind driven turbulence
Scientific Reports, 2016Co-Authors: Naohisa Takagaki, Ryoichi Kurose, Satoru Komori, Atsushi KimuraAbstract:The mass transfer across a sheared gas-liquid interface strongly depends on the Schmidt Number. Here we investigate the relationship between mass transfer coefficient on the liquid side, kL, and Schmidt Number, Sc, in the wide range of 0.7 ≤ Sc ≤ 1000. We apply a three-dimensional semi direct numerical simulation (SEMI-DNS), in which the mass transfer is solved based on an approximated deconvolution model (ADM) scheme, to wind-driven turbulence with mass transfer across a sheared wind-driven wavy gas-liquid interface. In order to capture the deforming gas-liquid interface, an arbitrary Lagrangian-Eulerian (ALE) method is employed. Our results show that similar to the case for flat gas-liquid interfaces, kL for the wind-driven wavy gas-liquid interface is generally proportional to Sc−0.5, and can be roughly estimated by the surface divergence model. This trend is endorsed by the fact that the mass transfer across the gas-liquid interface is controlled mainly by streamwise vortices on the liquid side even for the wind-driven turbulence under the conditions of low wind velocities without wave breaking.
-
subgrid scale scalar variance in high Schmidt Number turbulence
Aiche Journal, 2012Co-Authors: Ryoichi Kurose, Naohisa Takagaki, Takenobu Michioka, Naoki Kohno, Satoru KomoriAbstract:The subgrid scale (SGS) variance for a high-Schmidt-Number passive scalar of Sc >> 1 is measured using a high-resolution planar laser-induced fluorescence technique in a grid-generated turbulent liquid flow, and the values of the model coefficients in the scale-similarity model and the scalar-gradient model used for estimating the SGS scalar variance are experimentally evaluated. The results show that for both models, the measured values are much larger than the well-known values obtained in the previous studies done for non-high-Sc scalars of Sc ≅ 1. Similarly, the measured value of the model coefficient in the scalar-gradient model tends to be larger than the value estimated by the dynamic procedure. The increases in the measured values of the model coefficients for the high-Sc scalar can be explained by the presence of the viscous-convective range showing a nearly (−1)-slope in the high-waveNumber range of the power spectrum of concentration fluctuation. © 2011 American Institute of Chemical Engineers AIChE J, 2012
F Gori - One of the best experts on this subject based on the ideXlab platform.
-
flow evolution and mass transfer in a turbulent rectangular free jet of air with small laminar Schmidt Number
International Communications in Heat and Mass Transfer, 2019Co-Authors: Ivan Di Venuta, Andrea Boghi, I Petracci, Carlo Bartoli, F GoriAbstract:Abstract Numerical results are presented for flow evolution, mass transfer and evaluation of the turbulent Schmidt Number in a turbulent submerged free jet of air with small laminar Schmidt Number (Sc = 0.1). A series of Large Eddy Simulation (LES) are carried on in the Reynolds Number range from 5000 to 40,000. The numerical results are reported in terms of instantaneous and mean velocities, static pressure, passive scalar fields and turbulent Schmidt Number. The numerical results show that the instantaneous cross-stream velocity and the static pressure are null in the Negligible Disturbance Flow (NDF) and the Small Disturbance Flow (SDF) of the instantaneous jet evolution, allowing a new definition of NDF and SDF. Similarly, the numerical mean static pressure is null in the Undisturbed Region of Flow (URF) of the mean evolution, allowing a new definition of URF. The turbulent Schmidt Number shows differences at the two smallest Reynolds Numbers, Re = 5000 and 10,000, in comparison to the previous numerical results, obtained with a laminar Schmidt Number equal to Sc = 1. A theoretical model is proposed for the passive scalar diffusion in the Undisturbed Region of Flow (URF) and the Potential Core Region (PCR), under the hypotheses of self-similarity, according to the Tollmien and Gortler approaches. The solutions of the present theoretical models, at Sc = 0.1, are self-similar in the PCR and in good agreement with the LES numerical results of the passive scalar, while the passive scalar profiles are not self-similar in the URF at the smaller Reynolds Numbers, differently from what happens with a laminar Schmidt Number in the range 1–100. The theoretical model assumes a turbulent Schmidt Number inversely proportional to the mean velocity gradient in the PCR, as suggested by the LES results. The numerical results of the ScT in the URF are variable in the range 0–0.85, which is a value commonly suggested in the literature. In the PCR the values of ScT are variable between zero and a maximum which is one order of magnitude greater than in the URF.
-
passive scalar diffusion in three dimensional turbulent rectangular free jets with numerical evaluation of turbulent prandtl Schmidt Number
International Communications in Heat and Mass Transfer, 2018Co-Authors: Ivan Di Venuta, Andrea Boghi, Matteo Angelino, F GoriAbstract:Abstract The passive scalar spreading of fluids with laminar Prandtl or Schmidt Number, Pr, Sc, equal to 1 in turbulent rectangular submerged free jets is analyzed by means of numerical simulation and theoretical analysis in the Reynolds Number range 5000–40,000. The numerical investigation is carried out by means of a three-dimensional (3D) Large Eddy Simulation (LES) approach with the dynamic Smagorinsky model. A new mathematical model allows to obtain a simplified description of the passive scalar spreading in the largest area of the flow field, the Fully Developed Region (FDR). The present three-dimensional (3D) investigation shows that the passive scalar spreading follows a self-similarity law in the Fully Developed Region (FDR), as well as in the mean Undisturbed Region of Flow (URF) and in the Potential Core Region (PCR), similarly to what found in the Near Field Region (NFR) of rectangular submerged free jets, investigated with a two-dimensional (2D) approach. The turbulent Prandtl or Schmidt Number is evaluated numerically and is found to be inversely proportional to the mean velocity gradient in the PCR. The present 3D numerical results show that the turbulent Prandtl or Schmidt Number is zero in most part of the mean URF, and PCR, while it assumes different values outside. In the FDR the turbulent Prandtl or Schmidt Number is constant and approximately equal to 0.7, in agreement with the literature, showing that turbulence affects momentum and passive scalar in a different way.
Yasuhiko Sakai - One of the best experts on this subject based on the ideXlab platform.
-
power spectrum of high Schmidt Number scalar in a turbulent jet at a moderate reynolds Number
Experiments in Fluids, 2021Co-Authors: Koji Iwano, Yasuhiko Sakai, Jumpei Hosoi, Yasumasa ItoAbstract:The power spectrum of concentration fluctuation of high Schmidt Number dye ( $${\rm Sc}\simeq 2.9\times 10^3$$ ) was measured in a liquid-phase axisymmetric turbulent jet at the jet Reynolds Number of $$2.0\times 10^4$$ . We used the optical fiber LIF probe which has a spatial resolution of 2.8 $$\mu$$ m and a working distance of 140 $$\mu$$ m. It is confirmed that the probe can achieve high signal-to-noise ratio by using high concentration dye, which enabled us to examine the spectral shape almost up to the Batchelor scale for the present experimental condition. The measured power spectrum captures the transition from the inertial–convective range to the viscous–convective range at around $$k\eta _K=0.03$$ ( $$\eta _K$$ : Kolmogorov scale). The $$k^{-1}$$ scaling law for the power spectrum almost holds in the viscous–convective range. However, the spectrum does not perfectly follow the $$k^{-1}$$ scaling but has a small bump in the range. It is also shown that the small-scale concentration fluctuation largely contributes to the r.m.s value of concentration fluctuation.
-
mixing and chemical reaction at high Schmidt Number near turbulent nonturbulent interface in planar liquid jet
Physics of Fluids, 2015Co-Authors: Tomoaki Watanabe, Yasuhiko Sakai, Kouji Nagata, Takahiro Naito, Yasumasa ItoAbstract:This study investigates the mixing of reactive species at a high Schmidt Number (Sc ≈ 600) near the turbulent/nonturbulent (T/NT) interface in a planar liquid jet with a chemical reaction A + B → R. Reactants A and B are supplied from the jet and ambient flows, respectively. An I-type hot-film probe and optical fiber probe are used for the simultaneous measurements of the streamwise velocity, mixture fraction, and concentrations of all reactive species and for detecting the T/NT interface. Statistics conditioned on the time elapsed after interface detection are analyzed. The conditional mean mixture fraction and concentrations change sharply near the interface. The widths of these changes are independent of the chemical species. The conditional statistics reveal the dependence of the chemical reaction on the interface orientation. The segregation intensity near the interface shows that the mixing state of the two reactants also depends on the interface orientation. However, the large reaction rate near the interface is related to the large concentration of reactant A rather than the mixing state, because reactant A supplied from the jet tends to be deficient near the interface. Near the interface where the reaction rate is large, the concentration of the chemical product is also large. The difference in the product concentration between the different interface orientations is larger for the infinitely fast reaction (as investigated by using the equilibrium limit) than the finite Damkohler Number case, and the dependence of the chemical reaction on the interface orientation is expected to be significant for a fast chemical reaction.
-
turbulent Schmidt Number and eddy diffusivity change with a chemical reaction
Journal of Fluid Mechanics, 2014Co-Authors: Tomoaki Watanabe, Yasuhiko Sakai, Kouji Nagata, Osamu TerashimaAbstract:We provide empirical evidence that the eddy diffusivity and the turbulent Schmidt Number of species ( or ) change with a second-order chemical reaction ( ). In this study, concentrations of the reactive species and axial velocity are simultaneously measured in a planar liquid jet. Reactant A is premixed into the jet flow and reactant B is premixed into the ambient flow. An optical fibre probe based on light absorption spectrometry is combined with I-type hot-film anemometry to simultaneously measure concentration and velocity in the reactive flow. The eddy diffusivities and the turbulent Schmidt Numbers are estimated from the simultaneous measurement results. The results show that the chemical reaction increases ; is negative in the region where the mean concentration of reactant B decreases in the downstream direction, and is positive in the non-reactive flow in the entire region on the jet centreline. It is also shown that is positive in the upstream region whereas it is negative in the downstream region. The production terms of axial turbulent mass fluxes of reactant B and product R can produce axial turbulent mass fluxes opposite to the axial gradients of the mean concentrations. The changes in the production terms due to the chemical reaction result in the negative turbulent Schmidt Number of these species. These results imply that the gradient diffusion model using a global constant turbulent Schmidt Number poorly predicts turbulent mass fluxes in reactive flows.
-
Quantitative visualization of high-Schmidt-Number turbulent mixing in grid turbulence by means of PLIF
Journal of Visualization, 2012Co-Authors: Hiroki Suzuki, Kouji Nagata, Yasuhiko SakaiAbstract:Quantitative visualization of high-Schmidt-Number scalar fields has been performed in grid turbulence by means of a planar laser-induced fluorescence (PLIF) technique. The Reynolds Number based on a mesh size of the grid is 2500 and the Schmidt Number of the scalar is around 2100. To correct for the effects of various spatiotemporal variations such as quantum yield, a recently proposed correction method was introduced in the present experiment. In the present work, a PLIF experiment in combination with a calibration region installed outside of the test section is proposed. Visualizations of the instantaneous fluctuating scalar field suggest that mushroom-like structures accompanied by a pair of stirring structures, called engulfments, exist and contribute to large-scale scalar transfer. Visualization of the scalar dissipation field in the horizontal plane suggests that accumulation of the filament structures, which can be related to the mixing transition, locally exists around large-| c | regions, where | c | is the absolute value of the instantaneous fluctuating concentration. Thus, accumulation of the filament structures should be considered in the development of a turbulent mixing model for high-Schmidt-Number scalar transfer. Graphical abstract
-
high Schmidt Number scalar transfer in regular and fractal grid turbulence
Physica Scripta, 2010Co-Authors: Hiroki Suzuki, Yasuhiko Sakai, Kouji Nagata, Ryota UkaiAbstract:Turbulent mixing of high-Schmidt-Number passive scalars in regular and fractal grid turbulence is experimentally investigated using a water channel. A turbulence-generating grid is installed at the entrance of the test section, which is 1.5 m in length and 0.1 m×0.1 m in cross section. Two types of grids are used: one is a regular grid consisting of square-mesh and biplane constructions, and the other is a square-type fractal grid, which was first investigated by Hurst and Vassilicos (2007 Phys. Fluids 19 035103) and Seoud and Vassilicos (2007 Phys. Fluids 19 105108). The two grids have the same solidity of 0.36. The Reynolds Number based on the mesh size, ReM=U0Meff/ν, is 2500 in both flows, where U0 is the cross-sectionally averaged mean velocity, Meff is the effective mesh size and ν is the kinematic viscosity. A fluorescent dye (rhodamine B) is homogeneously premixed only in the lower stream and therefore the scalar mixing layers with an initial step profile develop downstream of the grids. The Schmidt Number of the dye is O(103). The time-resolved particle image velocimetry and the planar laser-induced fluorescence techniques are used to measure the velocity and concentration fields. The results show that the turbulent mixing in fractal grid turbulence is more strongly enhanced than that in regular grid turbulence for the same mesh Reynolds Number ReM. The profile of instantaneous scalar dissipation shows that scalar dissipation takes place locally even in the far downstream region at x/Meff=120 in fractal grid turbulence.
Donald R. Webster - One of the best experts on this subject based on the ideXlab platform.
-
scalar power spectra and turbulent scalar length scales of high Schmidt Number passive scalar fields in turbulent boundary layers
Physical Review Fluids, 2020Co-Authors: Mohammad Mohaghar, Lakshmi Prasad Dasi, Donald R. WebsterAbstract:High-Schmidt-Number passive scalar fields resulting from an isokinetic release in a turbulent boundary layer are characterized via turbulent scalar length scales, fractal geometry, intermittency, and power spectrum in the inertial-convective (I-C) and viscous-convective (V-C) regimes.The analysis indicates that the V-C scaling behavior deviated significantly from Batchelor's -1 scaling law for all Reynolds Numbers and initial nozzle diameters. The scalar fluctuation intermittency, which generates nonGaussian tails in the PDFs of the scalar fluctuations and produces a large dissipation rate, explains the steep spectral slope in the V-C regime.
-
The geometric properties of high-Schmidt-Number passive scalar iso-surfaces in turbulent boundary layers
Journal of Fluid Mechanics, 2007Co-Authors: Lakshmi Prasad Dasi, F. Schuerg, Donald R. WebsterAbstract:The geometric properties are quantified for concentration iso-surfaces of a high-Schmidt-Number passive scalar field produced by an iso-kinetic source with an initial finite characteristic length scale released into the inertial layer of fully developed open-channel-flow turbulent boundary layers. The coverage dimension and other measures of two-dimensional transects of the passive scalar iso-surfaces are found to be scale dependent. The coverage dimension is around 1.0 at the order of the Batchelor length scale and based on our data increases in a universal manner to reach a local maximum at a length scale around the Kolmogorov scale. We introduce a new parameter called the coverage length underestimate, which demonstrates universal behaviour in the viscous-convective regime for these data and hence is a potentially useful practical tool for many mixing applications. At larger scales (in the inertial-convective regime), the fractal geometry measures are dependent on the Reynolds Number, injection length scale, and concentration threshold of the iso-surfaces. Finally, the lacunarity of the iso-surface structure shows that the instantaneous scalar field is most inhomogenous around the length scale corresponding to the Kolmogorov scale.
