Three Dimensional Feature of Coherent Fine Scale Eddies in Homogeneous Isotropic Turbulence.

Tanahashi, Mamoru; Uddin, Md. Ashraf; Iwase, Shiki; Miyauchi, Toshio

doi:10.1299/kikaib.65.3237

Cited by 12 publications

(26 citation statements)

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“…3, the isosurfaces of a Q value defined with the second invariance of the velocity gradient tensor are shown. A positive Q value is shown to identify the core of coherent vortical structures (8) . Large-scale vortical structures such as vortex rings are strengthened from the inlet to the center of the computational volume (potential core length: approximately x/D = 6).…”

Section: Numerical Accuracymentioning

confidence: 95%

Direct Numerical Simulation of Jet Mixing Control Using Combined Jets

Tsujimoto

Shakouchi

Sasazaki

et al. 2006

JSME international journal. Ser. B, Fluids and thermal engineer

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In order to develop an efficient jet mixing method, direct numerical simulations of combined jets are carried out. The Reynolds number defined with a nozzle diameter is Re = 1 500. Spatial discretization is performed by adopting a hybrid scheme of a sixth order compact scheme in the streamwise direction and Fourier series in the cross section. The distance between two jets is fixed at six times the jet diameter, and the inclination angle of the jets is changed from 45 to 70 deg. The results reveal that the turbulence intensity increases with a decrease in the inclination angle and that the jet width increases via jet excitation. These findings suggest that the diverse requirements of jet mixing control can be satisfied by a flexible combination of jets.

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Section: Numerical Accuracymentioning

confidence: 95%

Direct Numerical Simulation of Jet Mixing Control Using Combined Jets

Tsujimoto

Shakouchi

Sasazaki

et al. 2006

JSME international journal. Ser. B, Fluids and thermal engineer

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show abstract

“…Note that the most expected diameter of these fine scale eddies is 8η and the maximum azimuthal velocity reaches to 3 ∼ 4u rms (40) . The number density of the fine scale eddies in the unit volume of the integral length scale (l 3 ) increases with the increase of Re λ (42) . For high Reynolds number hydrogen-air turbulent premixed flames, the wrinkling of the flame surfaces also increases and appearance of 3D structure increases because of high probability of the fine scale eddies which possess azimuthal velocity faster than S L (43) .…”

Section: Dns Of Turbulent Premixed Flamesmentioning

confidence: 99%

DNS and Combined Laser Diagnostics of Turbulent Combustion

Tanahashi

Sato

Shimura

et al. 2008

JTST

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With the developments of computer technologies, three-dimensional direct numerical simulations (DNS) of turbulent combustion have been realized with a detailed or reduced kinetic mechanism. The 3D DNS gives detailed information about turbulent flames, while there are few experimental techniques which have high accuracy enough to compare with DNS. In this paper, after showing summary of recent DNS of turbulent premixed flames, newly-developed laser diagnostics are presented. Simultaneous CH-OH planar laser induced fluorescence (PLIF) and stereoscopic particle image velocimetry (PIV) are used to investigate the local flame structure of the turbulent premixed flames. From CH-OH PLIF and PIV measurements, flame fronts are identified, and the curvature of the flame front and the tangential strain rate at the flame front are evaluated. The experimental results are compared with 3D DNS of hydrogen-air and methane-air turbulent premixed flames. The flame displacement speeds in turbulent premixed flames have been measured directly by the CH double-pulsed PLIF. Since the time interval of the successive CH PLIF can be selected arbitrarily, both of the large scale dynamics and local displacement of the flame front can be obtained. As an application of laser diagnostics for development of high-efficient and low-emission combustors, reconstruction of 3D flame structure is shown by using multiple-plane OH PLIF.

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“…The performance of our numerical code is also tested using no SGS model (NMU). All these computations are compared with the results from DNS based on a spectral method (3), (4) . The Smagorinsky closure applied to the SGS stress τ i j defined in Eq.…”

Section: Governing Equations and Sgs Modelmentioning

confidence: 99%

“…In this case only DSM is tested because the first case has revealed that DSM gives the most accurate results among the three models tested. In this case 128 3 numerical grid is expected to resolve the smallest turbulence scale while in the other two grids (64 3 and 32 3 grids) the effects of unresolved turbulent eddies must be properly modeled and our interest is whether the SGS model is capable of absorbing an appropriate amount of turbulent energy at the grid scale with least possible effects on the resolved energy spectra.…”

Section: Test Casesmentioning

confidence: 99%

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Large Eddy Simulation of Homogeneous Isotropic Turbulent Flow Using the Finite Element Method

Uddin

Kato

Yamade

et al. 2006

JSME international journal. Ser. B, Fluids and thermal engineer

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This paper presents results of validation study of large eddy simulation (LES) that is applied to homogeneous isotropic turbulence in order to assess its spectral accuracy. The LES is performed by using a streamline-upwind finite element method with second order accuracy both in time and space and the results are compared with those from direct numerical simulation (DNS) based on the spectral method. The validation tests are done by using Standard Smagorinsky Model (SSM) and Dynamic Smagorinsky Model (DSM), and include following two cases: a low Reynolds number case and a higher Reynolds number case. In the former case, the Reynolds number is low enough that the computational grid is capable of resolving all the turbulence scales. In this case our interest is in whether any effects of the subgrid scale (SGS) model should appropriately be dampened out. In the latter case, a relatively large Reynolds number is selected where effects of turbulent eddies that are not resolved by the computational grid should be properly taken into account by the SGS model. It is confirmed that DSM performs better than SSM for both cases and it gives good agreement with DNS results in terms of both spatial spectra and decay of the turbulence statistics. Visualization of the computed flow fields by the DSM also reveals existence of distinct, coherent and tube-like vortical structures similar to those found in instantaneous flow fields computed by the DNS.

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Three Dimensional Feature of Coherent Fine Scale Eddies in Homogeneous Isotropic Turbulence.

Cited by 12 publications

References 0 publications

Direct Numerical Simulation of Jet Mixing Control Using Combined Jets

Direct Numerical Simulation of Jet Mixing Control Using Combined Jets

DNS and Combined Laser Diagnostics of Turbulent Combustion

Large Eddy Simulation of Homogeneous Isotropic Turbulent Flow Using the Finite Element Method

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