TY - JOUR

T1 - Bifurcation diagram for two-dimensional steady flow and unsteady solutions in a curved square duct

AU - Mondal, Rabindra Nath

AU - Kaga, Yoshito

AU - Hyakutake, Toru

AU - Yanase, Shinichiro

N1 - Funding Information:
Rabindra Nath Mondal, one of the authors, would like to acknowledge gratefully the financial support from the Japanese Ministry of Education, Culture, Sports, Science and Technology (Monbukagakusho) for study in Japan. The authors also thank to Mr. T. Watanabe for his help in finding a new solution branch.

PY - 2007/5

Y1 - 2007/5

N2 - Flows through a curved duct of square cross-section are numerically studied by using the spectral method, and covering a wide range of curvature δ of the duct (0 < δ ≤ 0.5) and the Dean number Dn (0 < Dn ≤ 8000), where δ is non-dimensionalized by the half width of the square cross-section. The main concern is the relationship between the unsteady solutions, such as periodic, multi-periodic and chaotic solutions, and the bifurcation diagram of the steady solutions. It is found that the bifurcation diagram topologically changes if the curvature is increased and exceeds the critical value δc ≈ 0.279645, while it remains almost unchanged for δ < δc or δ > δc. A periodic solution is found to appear if the Dean number exceeds the bifurcation point, whether it is pitchfork or Hopf bifurcation, where no steady solution is stable. It is found that the bifurcation diagram and its topological change crucially affect the realizability of the steady and periodic solutions. Time evolution calculations as well as their spectral analysis show that the periodic solution turns to a chaotic solution if the Dn is further increased no matter what the curvature is. It is interesting that the chaotic solution is weak for smaller Dn, where the solution drifts among the steady solution branches, for larger Dn, on the other hand, the chaotic solution becomes strong, where the solution tends to get away from the steady solution branches.

AB - Flows through a curved duct of square cross-section are numerically studied by using the spectral method, and covering a wide range of curvature δ of the duct (0 < δ ≤ 0.5) and the Dean number Dn (0 < Dn ≤ 8000), where δ is non-dimensionalized by the half width of the square cross-section. The main concern is the relationship between the unsteady solutions, such as periodic, multi-periodic and chaotic solutions, and the bifurcation diagram of the steady solutions. It is found that the bifurcation diagram topologically changes if the curvature is increased and exceeds the critical value δc ≈ 0.279645, while it remains almost unchanged for δ < δc or δ > δc. A periodic solution is found to appear if the Dean number exceeds the bifurcation point, whether it is pitchfork or Hopf bifurcation, where no steady solution is stable. It is found that the bifurcation diagram and its topological change crucially affect the realizability of the steady and periodic solutions. Time evolution calculations as well as their spectral analysis show that the periodic solution turns to a chaotic solution if the Dn is further increased no matter what the curvature is. It is interesting that the chaotic solution is weak for smaller Dn, where the solution drifts among the steady solution branches, for larger Dn, on the other hand, the chaotic solution becomes strong, where the solution tends to get away from the steady solution branches.

KW - Bifurcation

KW - Chaos

KW - Curvature

KW - Curved square duct

KW - Linear stability

KW - Steady solutions

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U2 - 10.1016/j.fluiddyn.2006.10.001

DO - 10.1016/j.fluiddyn.2006.10.001

M3 - Article

AN - SCOPUS:34247229580

SN - 0169-5983

VL - 39

SP - 413

EP - 446

JO - Fluid Dynamics Research

JF - Fluid Dynamics Research

IS - 5

ER -