Håkan Wedin

Exact coherent structures in pipe flow: travelling wave solutions

Three-dimensional travelling wave solutions are found for pressure-driven fluid flow through a circular pipe. They consist of three well-defined flow features – streamwise rolls and streaks which dominate and streamwise-dependent wavy structures. The travelling waves can be classified by the

A new nonlinear vortex state in square-duct flow

m

Unstable flow structures in the Blasius boundary layer

-fold rotational symmetry they possess about the pipe axis with

Permeability models affecting nonlinear stability in the asymptotic suction boundary layer: the Forchheimer versus the Darcy model

m\,{=}\,1,2,3,4,5

Travelling Wave Solutions in Square Duct Flow

and

Nonlinear coherent structures in a square duct

6

Experimental Observation of Nonlinear Traveling Waves in Turbulent Pipe Flow

solutions identified. All are born out of saddle-node bifurcations with the lowest corresponding to

Effect of plate permeability on nonlinear stability of the asymptotic suction boundary layer

m\,{=}\,3

Sulla scia di Icaro

and traceable down to a Reynolds number (based on the mean velocity) of 1251. The new solutions are found using a constructive continuation procedure based upon key physical mechanisms thought generic to wall-bounded shear flows. It is believed that the appearance of these new alternative solutions to the governing equations as the Reynolds number is increased is a necessary precursor to the turbulent transition observed in experiments.

Self-sustained Flow States in a Square Duct

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.