The Experts below are selected from a list of 3651 Experts worldwide ranked by ideXlab platform
Masato Nagata - One of the best experts on this subject based on the ideXlab platform.
-
Asymmetric travelling waves in a Square Duct
Journal of Fluid Mechanics, 2012Co-Authors: Shinya Okino, Masato NagataAbstract:Two types of asymmetric solutions are found numerically in Square-Duct flow. They emerge through a symmetry-breaking bifurcation from the mirror-symmetric solutions discovered by Okino et al. ( J. Fluid Mech. , vol. 657, 2010, pp. 413–429). One of them is characterized by a pair of streamwise vortices and a low-speed streak localized near one of the sidewalls and retains the shift-and-reflect symmetry. The bifurcation nature as well as the flow structure of the solution show striking resemblance to those of the asymmetric solution in pipe flow found by Pringle & Kerswell ( Phys. Rev. Lett. , vol. 99, 2007, A074502), despite the geometrical difference between their cross-sections. The solution seems to be embedded in the edge state of Square-Duct flow identified by Biau & Bottaro ( Phil. Trans. R. Soc. Lond. A, vol. 367, 2009, pp. 529–544). The other solution deviates slightly from the mirror-symmetric solution from which it bifurcates: the shift-and-rotate symmetry is retained but the mirror symmetry is broken.
-
Travelling Wave Solutions in Square Duct Flow
Springer Proceedings in Physics, 2012Co-Authors: Shinya Okino, Masato Nagata, Håkan Wedin, Alessandro BottaroAbstract:Three nonlinear travelling wave solutions for Square Duct flow are discovered. One of them, the asymmetric solution, which is predicted by the stability analysis, bifurcates from the mirror-symmetric solution found by Okino et al., J. Fluid Mech. 657, 413 (2010). The solution is characterized by asymmetric crosssectional flow patterns with streamwise vortices attached to one of the side walls. The other two solutions, which have rotational symmetry by π and π /2, respectively, are found by a homotopy approach using artificially arranged body forces. Each of the new solutions shows striking similarity to that of pipe flow.
-
A new nonlinear vortex state in Square-Duct flow
Journal of Fluid Mechanics, 2010Co-Authors: Shinya Okino, Masato Nagata, Håkan Wedin, Alessandro BottaroAbstract:A new nonlinear travelling-wave solution for a flow through an isothermal Square Duct is discovered. The solution is found by a continuation approach in parameter space, starting from a case where the fluid is heated internally. The Reynolds number for which the travelling wave emerges is much lower than that of the solutions discovered recently by an analysis based on the self-sustaining process (Wedin et al., Phys. Rev. E, vol. 79, 2009, p. 065305; Uhlmann et al., Advances in Turbulence XII, 2009, pp. 585-588). Furthermore, the new travelling-wave solution is shown to be unstable from the onset.
-
Nonlinear coherent structures in a Square Duct
Springer Proceedings in Physics, 2009Co-Authors: Håkan Wedin, Alessandro Bottaro, Masato NagataAbstract:The transition to turbulence in a Square Duct is an intriguing problem of hydrodynamics and has been studied since the work by Nikuradse [5]. The mean secondary flow of the turbulent state is made up by 8 vortices in the cross-sectional plane with 2 vortices in each corner, symmetric about the diagonals [2, 3, 5, 6, 7, 8]. The underlying mechanism causing this flow has been related to anisotropic turbulent fluctuations. Recently it has been shown through numerical simulations that the flow at transitional Reynolds numbers (\(Re_{b} = \widehat{U}_{b}\widehat{b}/\widehat{v}\), where \(\widehat{U}_{b}\) is the bulk speed, \(\widehat{v}\) the kinematic viscosity and \(\widehat{b}\) the half Duct height) can feature instantaneous 4-vortex states (Biau & Bottaro [1] and Uhlmann et al [7]). The lower limit for transition in Re b is between 865 and 1077 [1, 7].
-
Three-dimensional traveling waves in a Square Duct.
Physical Review E, 2009Co-Authors: Håkan Wedin, Alessandro Bottaro, Masato NagataAbstract:A nonlinear streamwise traveling-wave solution is obtained by homotopy for Square Duct flow. For a particular symmetry of the perturbations, this wave comes into existence at about Re(b)=600 (based on half-Duct width and bulk speed) for a streamwise wave number alpha=0.85 . The resulting four-vortex mean flow resembles the transitional flow structures observed in previous simulations.
Alessandro Bottaro - One of the best experts on this subject based on the ideXlab platform.
-
Travelling Wave Solutions in Square Duct Flow
Springer Proceedings in Physics, 2012Co-Authors: Shinya Okino, Masato Nagata, Håkan Wedin, Alessandro BottaroAbstract:Three nonlinear travelling wave solutions for Square Duct flow are discovered. One of them, the asymmetric solution, which is predicted by the stability analysis, bifurcates from the mirror-symmetric solution found by Okino et al., J. Fluid Mech. 657, 413 (2010). The solution is characterized by asymmetric crosssectional flow patterns with streamwise vortices attached to one of the side walls. The other two solutions, which have rotational symmetry by π and π /2, respectively, are found by a homotopy approach using artificially arranged body forces. Each of the new solutions shows striking similarity to that of pipe flow.
-
A new nonlinear vortex state in Square-Duct flow
Journal of Fluid Mechanics, 2010Co-Authors: Shinya Okino, Masato Nagata, Håkan Wedin, Alessandro BottaroAbstract:A new nonlinear travelling-wave solution for a flow through an isothermal Square Duct is discovered. The solution is found by a continuation approach in parameter space, starting from a case where the fluid is heated internally. The Reynolds number for which the travelling wave emerges is much lower than that of the solutions discovered recently by an analysis based on the self-sustaining process (Wedin et al., Phys. Rev. E, vol. 79, 2009, p. 065305; Uhlmann et al., Advances in Turbulence XII, 2009, pp. 585-588). Furthermore, the new travelling-wave solution is shown to be unstable from the onset.
-
Nonlinear coherent structures in a Square Duct
Springer Proceedings in Physics, 2009Co-Authors: Håkan Wedin, Alessandro Bottaro, Masato NagataAbstract:The transition to turbulence in a Square Duct is an intriguing problem of hydrodynamics and has been studied since the work by Nikuradse [5]. The mean secondary flow of the turbulent state is made up by 8 vortices in the cross-sectional plane with 2 vortices in each corner, symmetric about the diagonals [2, 3, 5, 6, 7, 8]. The underlying mechanism causing this flow has been related to anisotropic turbulent fluctuations. Recently it has been shown through numerical simulations that the flow at transitional Reynolds numbers (\(Re_{b} = \widehat{U}_{b}\widehat{b}/\widehat{v}\), where \(\widehat{U}_{b}\) is the bulk speed, \(\widehat{v}\) the kinematic viscosity and \(\widehat{b}\) the half Duct height) can feature instantaneous 4-vortex states (Biau & Bottaro [1] and Uhlmann et al [7]). The lower limit for transition in Re b is between 865 and 1077 [1, 7].
-
Three-dimensional traveling waves in a Square Duct.
Physical Review E, 2009Co-Authors: Håkan Wedin, Alessandro Bottaro, Masato NagataAbstract:A nonlinear streamwise traveling-wave solution is obtained by homotopy for Square Duct flow. For a particular symmetry of the perturbations, this wave comes into existence at about Re(b)=600 (based on half-Duct width and bulk speed) for a streamwise wave number alpha=0.85 . The resulting four-vortex mean flow resembles the transitional flow structures observed in previous simulations.
-
Coherent flow states in a Square Duct
Physics of Fluids, 2008Co-Authors: Håkan Wedin, Alessandro Bottaro, Damien Biau, Masato NagataAbstract:The flow in a Square Duct is considered. Finite amplitude approximate traveling wave solutions, obtained using the self-sustaining-process approach introduced by Waleffe [Phys. Fluids 9, 883 (1997)], are obtained at low to moderate Reynolds numbers and used as initial conditions in direct numerical simulations. The ensuing dynamics is analyzed in a suitably defined phase space. Only one among the traveling wave solutions found is capable of surviving for a long time, with the flow trajectory forming quasiregular loops in phase space. Eventually, also this trajectory escapes along the manifold of a chaotic saddle and relaminarization ensues.
Luca Brandt - One of the best experts on this subject based on the ideXlab platform.
-
finite size spherical particles in a Square Duct flow of an elastoviscoplastic fluid an experimental study
Journal of Fluid Mechanics, 2020Co-Authors: Sagar Zade, Tafadzwa John Shamu, Fredrik Lundell, Luca BrandtAbstract:The present experimental study addresses the flow of a Yield Stress Fluid (YSF) with some elasticity (Carbopol gel) in a Square Duct. The behaviour of two fluids with lower and higher yield stress ...
-
inertial migration in dilute and semidilute suspensions of rigid particles in laminar Square Duct
Physical Review Fluids, 2017Co-Authors: Hamid Tabaei Kazerooni, Walter Fornari, Jeanette Hussong, Luca BrandtAbstract:We study the inertial migration of finite-size neutrally buoyant spherical particles in dilute and semidilute suspensions in laminar Square Duct flow. We perform several direct numerical simulation ...
-
Inertial migration in dilute and semidilute suspensions of rigid particles in laminar Square Duct flow
Physical Review Fluids, 2017Co-Authors: Hamid Tabaei Kazerooni, Walter Fornari, Jeanette Hussong, Luca BrandtAbstract:We study the inertial migration of finite-size neutrally buoyant spherical particles in dilute and semidilute suspensions in laminar Square Duct flow. We perform several direct numerical simulation ...
-
enhanced secondary motion of the turbulent flow through a porous Square Duct
Journal of Fluid Mechanics, 2015Co-Authors: Arghya Samanta, Ricardo Vinuesa, Philipp Schlatter, Iman Lashgari, Luca BrandtAbstract:Direct numerical simulations of the fully developed turbulent flow through a porous Square Duct are performed to study the effect of the permeable wall on the secondary cross-stream flow. The volume-averaged Navier–Stokes equations are used to describe the flow in the porous phase, a packed bed with porosity ${\it\varepsilon}_{c}=0.95$ . The porous Square Duct is computed at $\mathit{Re}_{b}\simeq 5000$ and compared with the numerical simulations of a turbulent Duct with four solid walls. The two boundary layers on the top wall and porous interface merge close to the centre of the Duct, as opposed to the channel, because the sidewall boundary layers inhibit the growth of the shear layer over the porous interface. The most relevant feature in the porous Duct is the enhanced magnitude of the secondary flow, which exceeds that of a regular Duct by a factor of four. This is related to the increased vertical velocity, and the different interaction between the ejections from the sidewalls and the porous medium. We also report a significant decrease in the streamwise turbulence intensity over the porous wall of the Duct (which is also observed in a porous channel), and the appearance of short spanwise rollers in the buffer layer, replacing the streaky structures of wall-bounded turbulence. These spanwise rollers most probably result from a Kelvin–Helmholtz type of instability, and their width is limited by the presence of the sidewalls.
Håkan Wedin - One of the best experts on this subject based on the ideXlab platform.
-
Travelling Wave Solutions in Square Duct Flow
Springer Proceedings in Physics, 2012Co-Authors: Shinya Okino, Masato Nagata, Håkan Wedin, Alessandro BottaroAbstract:Three nonlinear travelling wave solutions for Square Duct flow are discovered. One of them, the asymmetric solution, which is predicted by the stability analysis, bifurcates from the mirror-symmetric solution found by Okino et al., J. Fluid Mech. 657, 413 (2010). The solution is characterized by asymmetric crosssectional flow patterns with streamwise vortices attached to one of the side walls. The other two solutions, which have rotational symmetry by π and π /2, respectively, are found by a homotopy approach using artificially arranged body forces. Each of the new solutions shows striking similarity to that of pipe flow.
-
A new nonlinear vortex state in Square-Duct flow
Journal of Fluid Mechanics, 2010Co-Authors: Shinya Okino, Masato Nagata, Håkan Wedin, Alessandro BottaroAbstract:A new nonlinear travelling-wave solution for a flow through an isothermal Square Duct is discovered. The solution is found by a continuation approach in parameter space, starting from a case where the fluid is heated internally. The Reynolds number for which the travelling wave emerges is much lower than that of the solutions discovered recently by an analysis based on the self-sustaining process (Wedin et al., Phys. Rev. E, vol. 79, 2009, p. 065305; Uhlmann et al., Advances in Turbulence XII, 2009, pp. 585-588). Furthermore, the new travelling-wave solution is shown to be unstable from the onset.
-
Nonlinear coherent structures in a Square Duct
Springer Proceedings in Physics, 2009Co-Authors: Håkan Wedin, Alessandro Bottaro, Masato NagataAbstract:The transition to turbulence in a Square Duct is an intriguing problem of hydrodynamics and has been studied since the work by Nikuradse [5]. The mean secondary flow of the turbulent state is made up by 8 vortices in the cross-sectional plane with 2 vortices in each corner, symmetric about the diagonals [2, 3, 5, 6, 7, 8]. The underlying mechanism causing this flow has been related to anisotropic turbulent fluctuations. Recently it has been shown through numerical simulations that the flow at transitional Reynolds numbers (\(Re_{b} = \widehat{U}_{b}\widehat{b}/\widehat{v}\), where \(\widehat{U}_{b}\) is the bulk speed, \(\widehat{v}\) the kinematic viscosity and \(\widehat{b}\) the half Duct height) can feature instantaneous 4-vortex states (Biau & Bottaro [1] and Uhlmann et al [7]). The lower limit for transition in Re b is between 865 and 1077 [1, 7].
-
Three-dimensional traveling waves in a Square Duct.
Physical Review E, 2009Co-Authors: Håkan Wedin, Alessandro Bottaro, Masato NagataAbstract:A nonlinear streamwise traveling-wave solution is obtained by homotopy for Square Duct flow. For a particular symmetry of the perturbations, this wave comes into existence at about Re(b)=600 (based on half-Duct width and bulk speed) for a streamwise wave number alpha=0.85 . The resulting four-vortex mean flow resembles the transitional flow structures observed in previous simulations.
-
Coherent flow states in a Square Duct
Physics of Fluids, 2008Co-Authors: Håkan Wedin, Alessandro Bottaro, Damien Biau, Masato NagataAbstract:The flow in a Square Duct is considered. Finite amplitude approximate traveling wave solutions, obtained using the self-sustaining-process approach introduced by Waleffe [Phys. Fluids 9, 883 (1997)], are obtained at low to moderate Reynolds numbers and used as initial conditions in direct numerical simulations. The ensuing dynamics is analyzed in a suitably defined phase space. Only one among the traveling wave solutions found is capable of surviving for a long time, with the flow trajectory forming quasiregular loops in phase space. Eventually, also this trajectory escapes along the manifold of a chaotic saddle and relaminarization ensues.
Shinya Okino - One of the best experts on this subject based on the ideXlab platform.
-
Asymmetric travelling waves in a Square Duct
Journal of Fluid Mechanics, 2012Co-Authors: Shinya Okino, Masato NagataAbstract:Two types of asymmetric solutions are found numerically in Square-Duct flow. They emerge through a symmetry-breaking bifurcation from the mirror-symmetric solutions discovered by Okino et al. ( J. Fluid Mech. , vol. 657, 2010, pp. 413–429). One of them is characterized by a pair of streamwise vortices and a low-speed streak localized near one of the sidewalls and retains the shift-and-reflect symmetry. The bifurcation nature as well as the flow structure of the solution show striking resemblance to those of the asymmetric solution in pipe flow found by Pringle & Kerswell ( Phys. Rev. Lett. , vol. 99, 2007, A074502), despite the geometrical difference between their cross-sections. The solution seems to be embedded in the edge state of Square-Duct flow identified by Biau & Bottaro ( Phil. Trans. R. Soc. Lond. A, vol. 367, 2009, pp. 529–544). The other solution deviates slightly from the mirror-symmetric solution from which it bifurcates: the shift-and-rotate symmetry is retained but the mirror symmetry is broken.
-
Travelling Wave Solutions in Square Duct Flow
Springer Proceedings in Physics, 2012Co-Authors: Shinya Okino, Masato Nagata, Håkan Wedin, Alessandro BottaroAbstract:Three nonlinear travelling wave solutions for Square Duct flow are discovered. One of them, the asymmetric solution, which is predicted by the stability analysis, bifurcates from the mirror-symmetric solution found by Okino et al., J. Fluid Mech. 657, 413 (2010). The solution is characterized by asymmetric crosssectional flow patterns with streamwise vortices attached to one of the side walls. The other two solutions, which have rotational symmetry by π and π /2, respectively, are found by a homotopy approach using artificially arranged body forces. Each of the new solutions shows striking similarity to that of pipe flow.
-
A new nonlinear vortex state in Square-Duct flow
Journal of Fluid Mechanics, 2010Co-Authors: Shinya Okino, Masato Nagata, Håkan Wedin, Alessandro BottaroAbstract:A new nonlinear travelling-wave solution for a flow through an isothermal Square Duct is discovered. The solution is found by a continuation approach in parameter space, starting from a case where the fluid is heated internally. The Reynolds number for which the travelling wave emerges is much lower than that of the solutions discovered recently by an analysis based on the self-sustaining process (Wedin et al., Phys. Rev. E, vol. 79, 2009, p. 065305; Uhlmann et al., Advances in Turbulence XII, 2009, pp. 585-588). Furthermore, the new travelling-wave solution is shown to be unstable from the onset.
