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Georges Le Palec - One of the best experts on this subject based on the ideXlab platform.
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numerical study of turbulent round jet in a uniform counterflow using a second order Reynolds Stress Model
Journal of Hydro-environment Research, 2015Co-Authors: Amani Amamou, Sabra Habli, Nejla Mahjoub Said, Philippe Bournot, Georges Le PalecAbstract:Abstract A turbulent round jet issuing into a uniform counterflow stream is computationally investigated together with comparison with earlier experiments data, including velocity component along the jet axis and the radial direction. The simulation is carried out using the Reynolds Stress Model (RSM). Numerical results agree well with experimental results and the penetration and spreading of the jet are studied. The turbulence feature of the counterflowing jet indicates that the root-mean-square (rms) of axial velocity fluctuation ( u ′ 2 ¯ ) has two distinct peaks whose the second is a specificity of the jet into a counterflow, located within the region near the stagnation point. As the centerline velocity, the centerline temperature is found to decay more rapid when the jet-to-current velocity ratio is smaller. The spreading of the jet is also interpreted by the growth of both momentum width and temperature width of the counterflowing jet leading to that the presence of a counterflow enhances the mixing of the jet.
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Numerical study of turbulent round jet in a uniform counterflow using a second order Reynolds Stress Model
Journal of Hydro-environment Research, 2015Co-Authors: Amani Amamou, Sabra Habli, Nejla Mahjoub Said, Philippe Bournot, Georges Le PalecAbstract:A turbulent round jet issuing into a uniform counterflow stream is computationally investigated together with comparison with earlier experiments data, including velocity component along the jet axis and the radial direction. The simulation is carried out using the Reynolds Stress Model (RSM). Numerical results agree well with experimental results and the penetration and spreading of the jet are studied. The turbulence feature of the counterflowing jet indicates that the root-mean-square (rms) of axial velocity fluctuation (root u'(2)) has two distinct peaks whose the second is a specificity of the jet into a counterflow, located within the region near the stagnation point. As the centerline velocity, the centerline temperature is found to decay more rapid when the jet-to-current velocity ratio is smaller. The spreading of the jet is also interpreted by the growth of both momentum width and temperature width of the counterflowing jet leading to that the presence of a counterflow enhances the mixing of the jet. (C) 2015 International Association for Hydro-environment Engineering and Research, Asia Pacific Division. Published by Elsevier B.V. All rights reserved.
Yu-ning Huang - One of the best experts on this subject based on the ideXlab platform.
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Reynolds Stress Model involving the mean spin tensor.
Physical review. E Statistical nonlinear and soft matter physics, 2004Co-Authors: Yu-ning HuangAbstract:In this work, we develop a Reynolds Stress Model along the line of the approach presented by Commun. Nonlinear Sci. Numer. Simul. 9, 543 (2004)]], aiming to assess the role and contribution of the mean spin tensor in turbulence Modeling. Here, the constitutive functional for the Reynolds Stress depends on the mean spin tensor as well as the mean stretching tensor and its Jaumann derivative, the turbulent kinetic energy K , and the turbulent dissipation rate epsilon , which is at the complexity level of p=1,m=1 , and n=0 of a rate-type constitutive equation for the Reynolds Stress proposed in the aforementioned paper. The explicit form for the Reynolds Stress is obtained with recourse to the representation theorem and the theory of invariants developed in modern rational continuum mechanics, and, as an approximation, a nonlinear cubic K-epsilon Model is worked out in which the Model coefficients are analytically identified based on the experimental results of Tavoularis and Corrsin [J. Fluid Mech. 104, 311 (1981)]]. In addition, numerical results based on this Model, in the forms of employing the Jaumann derivative and the Oldroyd derivative, respectively, for homogeneous turbulent shear flow and fully developed turbulent flow over a backward-facing step, are presented in comparison with those obtained based on a few previously proposed linear and nonlinear K-epsilon Models, showing reasonably good agreement with the experimental results and the DNS data concerned and a better performance than the previously developed quadratic Models.
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Reynolds Stress Model involving the mean spin tensor.
Physical Review E, 2004Co-Authors: Yu-ning HuangAbstract:In this work, we develop a Reynolds Stress Model along the line of the approach presented by Huang [Commun. Nonlinear Sci. Numer. Simul. 9, 543 (2004)], aiming to assess the role and contribution of the mean spin tensor in turbulence Modeling. Here, the constitutive functional for the Reynolds Stress depends on the mean spin tensor as well as the mean stretching tensor and its Jaumann derivative, the turbulent kinetic energy $K$, and the turbulent dissipation rate $\ensuremath{\epsilon}$, which is at the complexity level of $p=1,m=1$, and $n=0$ of a rate-type constitutive equation for the Reynolds Stress proposed in the aforementioned paper. The explicit form for the Reynolds Stress is obtained with recourse to the representation theorem and the theory of invariants developed in modern rational continuum mechanics, and, as an approximation, a nonlinear cubic $K\text{\ensuremath{-}}\ensuremath{\epsilon}$ Model is worked out in which the Model coefficients are analytically identified based on the experimental results of Tavoularis and Corrsin [J. Fluid Mech. 104, 311 (1981)]. In addition, numerical results based on this Model, in the forms of employing the Jaumann derivative and the Oldroyd derivative, respectively, for homogeneous turbulent shear flow and fully developed turbulent flow over a backward-facing step, are presented in comparison with those obtained based on a few previously proposed linear and nonlinear $K\text{\ensuremath{-}}\ensuremath{\epsilon}$ Models, showing reasonably good agreement with the experimental results and the DNS data concerned and a better performance than the previously developed quadratic Models.
Sung-uk Choi - One of the best experts on this subject based on the ideXlab platform.
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turbulence Modeling of compound open channel flows with and without vegetation on the floodplain using the Reynolds Stress Model
Advances in Water Resources, 2006Co-Authors: Hyeongsik Kang, Sung-uk ChoiAbstract:Abstract A Reynolds Stress Model for the numerical simulation of compound open-channel flows with vegetation on the floodplain is described. The Reynolds Stress Model consists of various sub-Models such as Speziale et al.’s Model, Mellor and Herring’s Model, and Rotta’s Model for the pressure–strain correlation term, the turbulent diffusion term, and the dissipation term, respectively. For validation of the Model, plain compound open-channel flows are simulated. The computed results were compared with measured data by [Tominaga A, Nezu I. Turbulent structure in compound open-channel flows. J Hydraul Eng, ASCE 1991;117(1):21–41] and the results show that the Reynolds Stress Model successfully simulates the mean flow and turbulence structure of plain compound channel flows. The Model was then applied to compound open-channel flows with vegetated floodplains. Good agreement between the simulated results and data from an algebraic Stress Model by [Naot D, Nezu I, Nakagawa H. Hydrodynamic behavior of partly vegetated open channels. J Hydraul Eng, ASCE 1996;122(11):625–33] was found. However, it was shown that the RSM is capable of predicting the velocity dip and lateral shift in the maximum streamwise velocity, which were not observed in the data from algebraic Stress Modeling. Finally, a depth-averaged analysis of the streamwise momentum equation was performed to investigate the lateral momentum transfer in compound channel flows with vegetated floodplains. Compared with components by the secondary currents and Reynolds Stress, the drag force due to the presence of vegetation appears to be a factor in reducing the bottom shear Stress in both main channel and floodplain.
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numerical investigations of mean flow and turbulence structures of partly vegetated open channel flows using the Reynolds Stress Model
Journal of Hydraulic Research, 2006Co-Authors: Sung-uk Choi, Hyeongsik KangAbstract:A Reynolds Stress Model for the numerical simulation of partly-vegetated flows is presented. The Model uses Speziale, Sarkar, and Gatski's Model for the pressure–strain correlation, Mellor and Herring's Model and Rotta's Model for the diffusion and the dissipation rate of the Reynolds Stress, respectively. The Model is applied to partly-vegetated rectangular open-channel flows, and simulated results are compared with experimental data. The Model satisfactorily predicts mean flow and turbulence statistics. Through numerical experiments, the evolution of secondary current patterns and mean flow structure are presented for different densities of vegetation. A budget analysis of the streamwise vorticity equation is also performed to investigate the mechanism by which secondary currents in a partly-vegetated open-channel flow are generated. In the vegetated zone, the production by anisotropy is important in generating secondary currents over the entire depth, except for regions close to the free surface and th...
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3-D Numerical Simulation of Rectangular Open-Channel Flows by Reynolds Stress Model
2005Co-Authors: Hyeongsik Kang, Sung-uk ChoiAbstract:A Reynolds Stress Model for the numerical simulation of turbulent open-channel flows is developed in this study. The Reynolds Stress Model is comprised of Spezilae, Sarkar, and Gatski's Model for the pressure-strain term, Mellor and Herring's Model for the diffusion term, and Hanjalic and Launder's Model for the dissipation term. The developed Model is applied to a rectangular channel with a width to depth ratio of 2. The simulated mean flow and turbulence structures are compared with measured and computed data from the literature. The computed flow vectors show a small vortex, called inner secondary currents, located at the juncture of the side wall and the free surface as well as the free surface and bottom vortices. This small vortex causes a significant increase in the wall shear Stress in the vicinity of the free surface. A budget analysis of the stream-wise vorticity is carried out to investigate the mechanism by which the secondary currents are generated.
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3D numerical simulation of compound open-channel flow with vegetated floodplains by Reynolds Stress Model
KSCE Journal of Civil Engineering, 2005Co-Authors: Hyeongsik Kang, Sung-uk ChoiAbstract:This paper presents a Reynolds Stress Modeling of compound open-channel flows with vegetation on the floodplain. In the Reynolds Stress Model, we use the SSG Model by Speziale et al. , for the pressure-strain correlation term, Mellor and Herring's Model for the turbulent diffusion term, and Hanjalic and Launder's Model for the dissipation term. In order to take into account the anisotropy of turbulence due to the free surface, the combination of Shir's Model and Gibson and Launder's Model is included in the pressure-strain correlation Model. Model validations are carried out for the compound open-channel flows without vegetation. Then, the Model is applied to the compound open-channel flows with vegetated floodplains. The mean flow and turbulence structures are simulated and the impact of vegetation on the floodplains is investigated.
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Reynolds Stress Modeling of vegetated open-channel flows
Journal of Hydraulic Research, 2004Co-Authors: Sung-uk Choi, Hyeongsik KangAbstract:The Reynolds Stress Model is applied to open-channel flows with vegetation. For the computation of pressure-strain term, the Speziale, Sarkar, and Gatski's Model is employed. Mellor and Herring's Model and Rotta's Model are used for diffusion and dissipation rate of Reynolds Stress, respectively. Flow structures of open-channels under two vegetative conditions are simulated, namely submerged and emergent plants. Plain open-channel flows are also simulated for comparisons. Computed profiles are compared with the results from the κ-e Model and the algebraic Stress Model as well as measured data available in the literature. For the plain open-channel flow and the open-channel flow with emergent vegetation, the Reynolds Stress Model is observed to simulate the non-isotropic nature of the flows better than the algebraic Stress Model and the κ-e Model. For the open-channel flow with submerged vegetation, it is found that the Reynolds Stress Model predicts the mean flow and turbulence quantities best compared wi...
Hyeongsik Kang - One of the best experts on this subject based on the ideXlab platform.
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turbulence Modeling of compound open channel flows with and without vegetation on the floodplain using the Reynolds Stress Model
Advances in Water Resources, 2006Co-Authors: Hyeongsik Kang, Sung-uk ChoiAbstract:Abstract A Reynolds Stress Model for the numerical simulation of compound open-channel flows with vegetation on the floodplain is described. The Reynolds Stress Model consists of various sub-Models such as Speziale et al.’s Model, Mellor and Herring’s Model, and Rotta’s Model for the pressure–strain correlation term, the turbulent diffusion term, and the dissipation term, respectively. For validation of the Model, plain compound open-channel flows are simulated. The computed results were compared with measured data by [Tominaga A, Nezu I. Turbulent structure in compound open-channel flows. J Hydraul Eng, ASCE 1991;117(1):21–41] and the results show that the Reynolds Stress Model successfully simulates the mean flow and turbulence structure of plain compound channel flows. The Model was then applied to compound open-channel flows with vegetated floodplains. Good agreement between the simulated results and data from an algebraic Stress Model by [Naot D, Nezu I, Nakagawa H. Hydrodynamic behavior of partly vegetated open channels. J Hydraul Eng, ASCE 1996;122(11):625–33] was found. However, it was shown that the RSM is capable of predicting the velocity dip and lateral shift in the maximum streamwise velocity, which were not observed in the data from algebraic Stress Modeling. Finally, a depth-averaged analysis of the streamwise momentum equation was performed to investigate the lateral momentum transfer in compound channel flows with vegetated floodplains. Compared with components by the secondary currents and Reynolds Stress, the drag force due to the presence of vegetation appears to be a factor in reducing the bottom shear Stress in both main channel and floodplain.
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numerical investigations of mean flow and turbulence structures of partly vegetated open channel flows using the Reynolds Stress Model
Journal of Hydraulic Research, 2006Co-Authors: Sung-uk Choi, Hyeongsik KangAbstract:A Reynolds Stress Model for the numerical simulation of partly-vegetated flows is presented. The Model uses Speziale, Sarkar, and Gatski's Model for the pressure–strain correlation, Mellor and Herring's Model and Rotta's Model for the diffusion and the dissipation rate of the Reynolds Stress, respectively. The Model is applied to partly-vegetated rectangular open-channel flows, and simulated results are compared with experimental data. The Model satisfactorily predicts mean flow and turbulence statistics. Through numerical experiments, the evolution of secondary current patterns and mean flow structure are presented for different densities of vegetation. A budget analysis of the streamwise vorticity equation is also performed to investigate the mechanism by which secondary currents in a partly-vegetated open-channel flow are generated. In the vegetated zone, the production by anisotropy is important in generating secondary currents over the entire depth, except for regions close to the free surface and th...
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3-D Numerical Simulation of Rectangular Open-Channel Flows by Reynolds Stress Model
2005Co-Authors: Hyeongsik Kang, Sung-uk ChoiAbstract:A Reynolds Stress Model for the numerical simulation of turbulent open-channel flows is developed in this study. The Reynolds Stress Model is comprised of Spezilae, Sarkar, and Gatski's Model for the pressure-strain term, Mellor and Herring's Model for the diffusion term, and Hanjalic and Launder's Model for the dissipation term. The developed Model is applied to a rectangular channel with a width to depth ratio of 2. The simulated mean flow and turbulence structures are compared with measured and computed data from the literature. The computed flow vectors show a small vortex, called inner secondary currents, located at the juncture of the side wall and the free surface as well as the free surface and bottom vortices. This small vortex causes a significant increase in the wall shear Stress in the vicinity of the free surface. A budget analysis of the stream-wise vorticity is carried out to investigate the mechanism by which the secondary currents are generated.
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3D numerical simulation of compound open-channel flow with vegetated floodplains by Reynolds Stress Model
KSCE Journal of Civil Engineering, 2005Co-Authors: Hyeongsik Kang, Sung-uk ChoiAbstract:This paper presents a Reynolds Stress Modeling of compound open-channel flows with vegetation on the floodplain. In the Reynolds Stress Model, we use the SSG Model by Speziale et al. , for the pressure-strain correlation term, Mellor and Herring's Model for the turbulent diffusion term, and Hanjalic and Launder's Model for the dissipation term. In order to take into account the anisotropy of turbulence due to the free surface, the combination of Shir's Model and Gibson and Launder's Model is included in the pressure-strain correlation Model. Model validations are carried out for the compound open-channel flows without vegetation. Then, the Model is applied to the compound open-channel flows with vegetated floodplains. The mean flow and turbulence structures are simulated and the impact of vegetation on the floodplains is investigated.
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Reynolds Stress Modeling of vegetated open-channel flows
Journal of Hydraulic Research, 2004Co-Authors: Sung-uk Choi, Hyeongsik KangAbstract:The Reynolds Stress Model is applied to open-channel flows with vegetation. For the computation of pressure-strain term, the Speziale, Sarkar, and Gatski's Model is employed. Mellor and Herring's Model and Rotta's Model are used for diffusion and dissipation rate of Reynolds Stress, respectively. Flow structures of open-channels under two vegetative conditions are simulated, namely submerged and emergent plants. Plain open-channel flows are also simulated for comparisons. Computed profiles are compared with the results from the κ-e Model and the algebraic Stress Model as well as measured data available in the literature. For the plain open-channel flow and the open-channel flow with emergent vegetation, the Reynolds Stress Model is observed to simulate the non-isotropic nature of the flows better than the algebraic Stress Model and the κ-e Model. For the open-channel flow with submerged vegetation, it is found that the Reynolds Stress Model predicts the mean flow and turbulence quantities best compared wi...
Amani Amamou - One of the best experts on this subject based on the ideXlab platform.
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numerical study of turbulent round jet in a uniform counterflow using a second order Reynolds Stress Model
Journal of Hydro-environment Research, 2015Co-Authors: Amani Amamou, Sabra Habli, Nejla Mahjoub Said, Philippe Bournot, Georges Le PalecAbstract:Abstract A turbulent round jet issuing into a uniform counterflow stream is computationally investigated together with comparison with earlier experiments data, including velocity component along the jet axis and the radial direction. The simulation is carried out using the Reynolds Stress Model (RSM). Numerical results agree well with experimental results and the penetration and spreading of the jet are studied. The turbulence feature of the counterflowing jet indicates that the root-mean-square (rms) of axial velocity fluctuation ( u ′ 2 ¯ ) has two distinct peaks whose the second is a specificity of the jet into a counterflow, located within the region near the stagnation point. As the centerline velocity, the centerline temperature is found to decay more rapid when the jet-to-current velocity ratio is smaller. The spreading of the jet is also interpreted by the growth of both momentum width and temperature width of the counterflowing jet leading to that the presence of a counterflow enhances the mixing of the jet.
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Numerical study of turbulent round jet in a uniform counterflow using a second order Reynolds Stress Model
Journal of Hydro-environment Research, 2015Co-Authors: Amani Amamou, Sabra Habli, Nejla Mahjoub Said, Philippe Bournot, Georges Le PalecAbstract:A turbulent round jet issuing into a uniform counterflow stream is computationally investigated together with comparison with earlier experiments data, including velocity component along the jet axis and the radial direction. The simulation is carried out using the Reynolds Stress Model (RSM). Numerical results agree well with experimental results and the penetration and spreading of the jet are studied. The turbulence feature of the counterflowing jet indicates that the root-mean-square (rms) of axial velocity fluctuation (root u'(2)) has two distinct peaks whose the second is a specificity of the jet into a counterflow, located within the region near the stagnation point. As the centerline velocity, the centerline temperature is found to decay more rapid when the jet-to-current velocity ratio is smaller. The spreading of the jet is also interpreted by the growth of both momentum width and temperature width of the counterflowing jet leading to that the presence of a counterflow enhances the mixing of the jet. (C) 2015 International Association for Hydro-environment Engineering and Research, Asia Pacific Division. Published by Elsevier B.V. All rights reserved.