TY - JOUR

T1 - Laminar-turbulent transition in Poiseuille pipe flow subjected to periodic perturbation emanating from the wall

AU - Eliahou, S.

AU - Tumin, A.

AU - Wygnanski, I.

PY - 1998/4/25

Y1 - 1998/4/25

N2 - Transition in fully developed circular pipe flow was investigated experimentally by the introduction of periodic perturbations. The simultaneous excitation of the azimuthal periodic modes m = +2 and m = -2 was chosen for detailed analysis. The experiments were carried out at three amplitudes. At the smallest amplitude the disturbances decayed in the direction of streaming. At intermediate input amplitude the disturbances amplified initially but then decayed with increasing distance downstream. Their growth was accompanied by the appearance of higher harmonics. At still higher amplitudes transition occurred. A mean velocity distortion corresponding to an azimuthal index of m = 4 was observed at the intermediate and at the higher levels of forcing When four stationary jets were introduced through the wall to emulate a similar mean velocity distortion, transition was observed at smaller amplitudes of forcing at modes ±2. Thus, weak longitudinal vortices provide an added instability needed to generate a secondary disturbance which, in turn, amplifies the steady vortical structures introduced by the jets. Such vortices may also be generated through the interaction of time-periodic helical modes.

AB - Transition in fully developed circular pipe flow was investigated experimentally by the introduction of periodic perturbations. The simultaneous excitation of the azimuthal periodic modes m = +2 and m = -2 was chosen for detailed analysis. The experiments were carried out at three amplitudes. At the smallest amplitude the disturbances decayed in the direction of streaming. At intermediate input amplitude the disturbances amplified initially but then decayed with increasing distance downstream. Their growth was accompanied by the appearance of higher harmonics. At still higher amplitudes transition occurred. A mean velocity distortion corresponding to an azimuthal index of m = 4 was observed at the intermediate and at the higher levels of forcing When four stationary jets were introduced through the wall to emulate a similar mean velocity distortion, transition was observed at smaller amplitudes of forcing at modes ±2. Thus, weak longitudinal vortices provide an added instability needed to generate a secondary disturbance which, in turn, amplifies the steady vortical structures introduced by the jets. Such vortices may also be generated through the interaction of time-periodic helical modes.

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U2 - 10.1017/S002211209800888X

DO - 10.1017/S002211209800888X

M3 - Article

AN - SCOPUS:0032047020

SN - 0022-1120

VL - 361

SP - 333

EP - 349

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

ER -