Experimental investigation of laminar turbulent intermittency in pipe flow

Abstract

In shear flows turbulence first occurs in the form of localized structures (puffs/spots) surrounded by laminar fluid. We here investigate such spatially intermittent flows in a pipe experiment showing that turbulent puffs have a well defined interaction distance, which sets the minimum spacing of puffs as well as the maximum observable turbulent fraction. Two methodologies are employed here. Starting from a laminar flow puffs can be created by locally injecting a jet of fluid through the pipe wall. When the perturbation is applied periodically at low frequencies, as expected, a regular sequence of puffs is observed where the puff spacing is given by the ratio of the mean flow speed to the perturbation frequency. On the other hand, at large frequencies puffs are found to interact and annihilate each other. Varying the perturbation frequency an interaction distance can be determined. In the second set of experiments, the Reynolds number is reduced suddenly from fully developed turbulence to the intermittent regime.The resulting flow reorganizes itself to a sequence of constant size puffs which, unlike in Couette and Taylor Couette flow are randomly spaced. The minimum distance between the turbulent patches is identical to the puff interaction length. The puff interaction length is found to be in excellent agreement with the wavelength of regular stripe and spiral patterns in plane Couette and Taylor-Couette flow. We propose that the same interaction mechanism is present in these flows.

References in corpus (4)

• Computational Study of Turbulent-Laminar Patterns in Couette Flow
• Snakes and ladders: localized solutions of plane Couette flow
• Mean flow of turbulent-laminar patterns in plane Couette flow
• On the transient nature of localized pipe flow turbulence

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• On the nature of laminar-turbulence intermittency in shear flows
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• Patterns in transitional shear turbulence. Part 2: Emergence and optimal wavelength
• Phase transition to turbulence via moving fronts
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• Deterministic and stochastic aspects of the transition to turbulence
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• A traveling wave bifurcation analysis of turbulent pipe flow
• Dynamics of turbulent plugs in a superfluid ${}^4$He channel counterflow
• A cascade model for the discontinuous absorbing phase transition between turbulent and laminar flows