TY - JOUR

T1 - Laminar-to-turbulent transition of pipe flows through puffs and slugs

AU - Nishi, Mina

AU - Ünsal, Bülent

AU - Durst, Franz

AU - Biswas, Gautam

N1 - Funding Information:
Special thanks are due to Dr Jovan Jovanović for the valuable discussions. The authors are grateful to the LSTM workshop, especially Mr Jürgen Heubeck, for support during construction of the test facilities. The authors further acknowledge especially Professor Dr Antonio Delgado for his generous support so that the present investigations could be conducted at LSTM-Erlangen. The research stay of G. B. was supported by a DAAD-DST, PPP program.

PY - 2008

Y1 - 2008

N2 - Laminar-to-turbulent transition of pipe flows occurs, for sufficiently high Reynolds numbers, in the form of slugs. These are initiated by disturbances in the entrance region of a pipe flow, and grow in length in the axial direction as they move downstream. Sequences of slugs merge at some distance from the pipe inlet to finally form the state of fully developed turbulent pipe flow. This formation process is generally known, but the randomness in time of naturally occurring slug formation does not permit detailed study of slug flows. For this reason, a special test facility was developed and built for detailed investigation of deterministically generated slugs in pipe flows. It is also employed to generate the puff flows at lower Reynolds numbers. The results reveal a high degree of reproducibility with which the triggering device is able to produce puffs. With increasing Reynolds number, 'puff splitting' is observed and the split puffs develop into slugs. Thereafter, the laminar-to-turbulent transition occurs in the same way as found for slug flows. The ring-type obstacle height, h, required to trigger fully developed laminar flows to form first slugs or puffs is determined to show its dependence on the Reynolds number, Re = DU/ν (where D is the pipe diameter, U is the mean velocity in the axial direction and ν is the kinematic viscosity of the fluid). When correctly normalized, h+ turns out to be independent of Reτ (where h+ = hUτ/ν, Reτ = DUτ/ν and Uτ = √τwρ; τw is the wall shear stress and ρ is the density of the fluid).

AB - Laminar-to-turbulent transition of pipe flows occurs, for sufficiently high Reynolds numbers, in the form of slugs. These are initiated by disturbances in the entrance region of a pipe flow, and grow in length in the axial direction as they move downstream. Sequences of slugs merge at some distance from the pipe inlet to finally form the state of fully developed turbulent pipe flow. This formation process is generally known, but the randomness in time of naturally occurring slug formation does not permit detailed study of slug flows. For this reason, a special test facility was developed and built for detailed investigation of deterministically generated slugs in pipe flows. It is also employed to generate the puff flows at lower Reynolds numbers. The results reveal a high degree of reproducibility with which the triggering device is able to produce puffs. With increasing Reynolds number, 'puff splitting' is observed and the split puffs develop into slugs. Thereafter, the laminar-to-turbulent transition occurs in the same way as found for slug flows. The ring-type obstacle height, h, required to trigger fully developed laminar flows to form first slugs or puffs is determined to show its dependence on the Reynolds number, Re = DU/ν (where D is the pipe diameter, U is the mean velocity in the axial direction and ν is the kinematic viscosity of the fluid). When correctly normalized, h+ turns out to be independent of Reτ (where h+ = hUτ/ν, Reτ = DUτ/ν and Uτ = √τwρ; τw is the wall shear stress and ρ is the density of the fluid).

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U2 - 10.1017/S0022112008003315

DO - 10.1017/S0022112008003315

M3 - Article

AN - SCOPUS:54549110353

SN - 0022-1120

VL - 614

SP - 425

EP - 446

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

ER -