Generality of controlled localized turbulence beyond pipe flow

Determine whether the localized-turbulence behavior produced by streamwise-travelling waves of azimuthal wall velocity is characteristic of pipe flow alone or also occurs in other flow geometries.

Background

The paper demonstrates that streamwise-travelling waves of azimuthal wall velocity can produce laminarization or spatially localized turbulent puffs in pipe flow at a bulk Reynolds number of 4900. These controlled puffs differ from canonical pipe-flow puffs in several respects, including their substantially higher convection speeds and their occurrence at a Reynolds number well above the canonical threshold for sustained turbulence.

The authors note that comparable localized turbulence has not been observed in plane channel flow, although intermittent laminar–turbulent patterns occur under subcritical conditions in plane Poiseuille, plane Couette, and Taylor–Couette flows. The unresolved issue is whether the controlled behavior is specific to pipe geometry or reflects a more general response of subcritical shear flows to active control.

References

Whether this behavior is characteristic of pipe flow alone also remains unclear.

— Drag reduction and subcritical turbulence in controlled pipe flows  (2608.30452 - Gallorini et al., 31 Aug 2026) in Section 5, Concluding discussion

Interesting questions are whether such intermittent patterns appear when control is applied to these other geometries, and whether puff-like structures comparable to those observed here exist in geometries with similar transition behavior (e.g., the square duct).

— Drag reduction and subcritical turbulence in controlled pipe flows  (2608.30452 - Gallorini et al., 31 Aug 2026) in Section 5, Concluding discussion