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A Numerical analysis has been carried out of developing turbulent flow in S-shaped duct with a square cross section at a Reynolds number of 4 x 10~4. The S-duct was formed from two 22.5 degree bends with 40mm hydraulic diameter an...
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A Numerical analysis has been carried out of developing turbulent flow in S-shaped duct with a square cross section at a Reynolds number of 4 x 10~4. The S-duct was formed from two 22.5 degree bends with 40mm hydraulic diameter and 280mm mean radius of curvature. Straight ducts with hydraulic diameters of 7.5 and 50 are attached to the inlet and outlet planes of the S-duct, respective- ly. In calculation, an algebraic Reynolds stress model was adopted in order to predict anisotropic turbulence precisely, and boundary-fitted corrdinate system was introduced as the method of coordi- nate transformation.
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A numerical analysis has been performed for developing turbulent flow of non--Newtonian fluid in eccentric annular passage. Several calculations have been carried out to examine the drag reduction with decreasing power index of po...
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A numerical analysis has been performed for developing turbulent flow of non--Newtonian fluid in eccentric annular passage. Several calculations have been carried out to examine the drag reduction with decreasing power index of power--law fluids and the reduction of skin friction factor with increasing eccentricity defined by the distance between the centers of the inner and outer pipes for Newtonian fluid. In numerical analysis, the power law model for non--Newtonian fluid and an algebraic Reynolds stress model for turbulent flow were adopted in order to predict precisely non- Newtonian flow behaviour. Boundary--fitted coordinate system was introduced as the method of coordinate transformation. The numerical results are compared with the experimental data involv- ing stramwise velocity and fluctuating velocities in axial, radial and tangential directions. As a result of comparison with the experiment, it was found that the present method could predict well the streamwise meam-velocity in both fluids and reproduce the secondary flow of the second kind generated by anisotoropic turbulence. As for the comparison of fluctuating velocities, the agreement with experimental data is more satisfied for Newtonian fluid than for non--Newtonian fluid. The calculated results also suggest that the drag reduction with polymer solution is realized by the present method as well as the experiment and the phenomenon of decaying fluctuating velocity with decreasing power index is predicted.
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In this paper we describe numerical analysis to investigate the three-dimensional turbulent structure and fluid flow behavior in a square-to-circular transition duct. The hydraulic diameter, 40 mm, was the same in the square inlet...
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In this paper we describe numerical analysis to investigate the three-dimensional turbulent structure and fluid flow behavior in a square-to-circular transition duct. The hydraulic diameter, 40 mm, was the same in the square inlet and round exit sections, resulting in a cross-sectional area reduction of 21.5 percent. The transition takes place over two hydraulic diameters. In the calcula- tion, an algebraic Reynolds stress model combined with a boundary-fitted coordinate system is applied to a square-to-circular transition duct in order to solve anisotropic turbulent flow precisely.
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The flow behavior of viscoelastic non-Newtonian fluid in circular and non-circular ducts is of special engineering interest. Therefore a numerical analysis has been performed for viscoelastic non- Newtonian fluid in elliptical duc...
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The flow behavior of viscoelastic non-Newtonian fluid in circular and non-circular ducts is of special engineering interest. Therefore a numerical analysis has been performed for viscoelastic non- Newtonian fluid in elliptical duct. Special attention is paid for the generation of secondary flow for laminar flow by using two kinds of constitutive equation, i. e., Maxwell and Reiner-Rivlin models. As for Maxwell model, body force caused by the elastic stress is approximated by linear source term. In calculation, viscosity was represented by adopting power-law fiuid and boundary-fitted coordinate system was introduced as the method of coordinate transformation. The calculated results of two models show the secondary flow in elliptical duct as the same as theoretically analyzed by Green and Rivlin. Adding to the prediction of secondary flow, the generation mechanism of secondary flow has been argued by evaluating the production terms of the transport equation for streamwise vorticity. As a result of this examination, it was found that the term of viscous diffusion and the term containing second normal stress difference played an important role in producing the secondary flow near the wall. At the same time, it is interested phenomenon that the circular direction of secondary flow for viscoelastic fluid is opposite sigh to that of secondary flow for Newtonian turbulent flow. As its cause, the present study clarified that the term containing second normal stress difference of viscoelastic fluid is the same type equation for that of turbulence, while the sign of its term for visco
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A numerical analysis has been performed for developing turbulent flow of non--Newtonian fluid in curved pipe, Numerical results are shown in two cases of power-law fluids, i. e. power index 0.76 and 0.9, at Reynolds number 19000. ...
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A numerical analysis has been performed for developing turbulent flow of non--Newtonian fluid in curved pipe, Numerical results are shown in two cases of power-law fluids, i. e. power index 0.76 and 0.9, at Reynolds number 19000. The ratio of bend mean radius of curvature to radius is 10 and straight duct of 40 and 100 diameters are attached to the inlet and outlet of the bend, respectively. In numerical analysis, an algebraic Reynolds stress model was adopted in order to predict precisely the anisotropic turbulent flow and boundary-fitted coordinate system was introduced as the method of coordinate transformation. The numerical results are compared with the experimental data mea- sured by laser-Doppler anemometer. Mean velocity and fluctuating velocity in axial direction are examined into detail to clarify the validity of the turbulent model and present numerical method. As a result of this research, it is found that the present method could predict well the streamwise mean- velocity in both cases of power-law fluids. As for the comparison of fluctuating velocity, characteris- tic features are reproduced except for the outer region of pipes. The present method predicts its value in outer regin smaller than that of the experiment, while the present method realized the phenomenon of decaying mean fluctuating velocity with decreasing power index. The results of comparison with the experimental data suggest that algebraic turbulent model is applicable to the non-Nowtonian fluid although agreement between both results is certainly not perfect in all detail.
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A numerical analysis has been performed for turbulent flow developing in longitudinally finned tubes. Three tube geometries were calculated; two 8-finned tubes (fin hight-to-radius ratios of 0.333 and 0.167) and one 16-finned tube...
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A numerical analysis has been performed for turbulent flow developing in longitudinally finned tubes. Three tube geometries were calculated; two 8-finned tubes (fin hight-to-radius ratios of 0.333 and 0.167) and one 16-finned tube (fin height-to-radius ratio of 0. 167). In calculations, an algebraic Reynolds stress model was adopted in order to predict precisely the secondary flow of the second kind induced by anisotropic turbulence and boundary-fitted coordinate system was introduced as the method of coordinate transformation. Mean velocities in axial, radial and circumferencial directions, pressure drop in tubues and primary shear stress distribution are compared with the experimental data. As a result of this analysis, it was found that the present method could predict well the streamwise mean-velocity. In the case of 8-finned tube of fin height-to-radius ratio 0.333, two secondary flow cells which were measured in experiment, were reproduced by the present turublent model although a small intensity of secondary flow were observed compared with the experiment. Moreover, numerical results suggest that these two secondary flow cells disapper in 8-finned tube of fin height-to-radius ratio 0.167 and the secondary flow has a influence on the wall shear stress distribution. The calculated results also show that the turbulence in the interfin region is greatly reduced as well as the experiment.
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In this study, numerical analysis has been performed to clarify the assessment of volume tracking algorithms in a three-dimensional flow field dominated by surface tension. The FLAIR method has been extended to three-dimensional p...
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In this study, numerical analysis has been performed to clarify the assessment of volume tracking algorithms in a three-dimensional flow field dominated by surface tension. The FLAIR method has been extended to three-dimensional problems in this study. The distinct feature of FLAIR developed in two-dimension is that the slope of line segment is estimated based only on two neighboring volume fractions. This feature is also adopted in the three-dimensional FLAIR method proposed in this study, even if the three-dimensional slope of interface is neglected. This three-dimensional FLAIR is applied to a non-straining flow field and a surface tension dominated flow field. The results are compared with those of the donor-acceptor method, the SURFER method and the CIP method with digitization. Consequently, it has been found that the precision of translation of interface is much more improved by the use of the CIP method with digitization and the three-dimensional FLAIR method than that of the other methods. However, the CIP method with digitization will produce an uneven interface.
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The numerical study has been performed on turbulent flow developing in a 90 degree curved duct of rectangular crosssection and an aspect ratio of 6. The ratio of bend mean radius of curvature to hydraulic diameter is 2.04 and stra...
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The numerical study has been performed on turbulent flow developing in a 90 degree curved duct of rectangular crosssection and an aspect ratio of 6. The ratio of bend mean radius of curvature to hydraulic diameter is 2.04 and straight ducts of 7.5 and 25.5 width are attached to the inlet and outlet of the bend, respectively. In addition to this straight duct, two-dimensional lateral contraction of the wind tunnel with an area ratio of 6 is considered as the numerical domain as well as the experimental apparatus.
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Numerical data are reported for turbulent flow developing in a right traiangular duct with internal angles of 60 and 30 deg. An overwhelming number of numerical and experimental studies on noncircular ducts have dealt with ducts t...
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Numerical data are reported for turbulent flow developing in a right traiangular duct with internal angles of 60 and 30 deg. An overwhelming number of numerical and experimental studies on noncircular ducts have dealt with ducts that contain one or more symmetry planes. In contrast, this duct has no symmetry planes. In the calculation, and algebraic Renolds stress model was adopted in order to predict anisotropic turbulence precisely, and a boundary fitted coordinate system was introduced as the method of coordinate transformation.
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Numerical Simulation has been performed for developing turbulent flow in S-shaped duct with a square section at a Reynolds number of 4 x 10~4. The S-duct was formed from two 22.5 degree bends with 40 mm hydraulic diameter and 280 ...
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Numerical Simulation has been performed for developing turbulent flow in S-shaped duct with a square section at a Reynolds number of 4 x 10~4. The S-duct was formed from two 22.5 degree bends with 40 mm hydraulic diameter and 280 mm mean radius of curvature. Straight ducts with hydraulic diameters of 7.5 and 50 are attached to the inlet and outlet planes of the S-duct, respectively. In calculation, an algebraic Reynolds stress model was adopted in order to predict anisotropic turbulent flow precisely, and a boundary-fitted coordinate system was introduced for coordinate transforma- tion.
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