Forced laminar-to-turbulent transition of pipe flows

Durst, F.; Ünsal, Bülent

doi:10.1017/s0022112006000528

Cited by 60 publications

(60 citation statements)

References 10 publications

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“…They concluded that a critical amplitude of disturbance was needed to cause a transition and it depends on the Reynolds number. Durst &Ünsal (2006) highlighted the influence of the disturbed wall fence height and the results showed a dependence of critical Reynolds number on the normalized height of their disturbances.…”

Section: Introductionmentioning

confidence: 94%

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

Nishi¹,

Ünsal²,

Durst³

et al. 2008

J. Fluid Mech.

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122

100

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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 Re τ (where h + = hU τ /ν, Re τ = DU τ /ν and U τ = √ τ w /ρ; τ w is the wall shear stress and ρ is the density of the fluid).

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Section: Introductionmentioning

confidence: 94%

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

Nishi¹,

Ünsal²,

Durst³

et al. 2008

J. Fluid Mech.

Self Cite

122

100

View full text Add to dashboard Cite

show abstract

“…The size of the ring-type constriction is based on an a previous study by Durst and Ü nsal 29 who provide an indication of the mean Reynolds number at which transition is expected to occur. We should note here that the type of disturbance may have an influence on the critical Reynolds number.…”

Section: Experimental Techniques a Flow Facilitymentioning

confidence: 99%

“…For the axial component, a large overshoot is shown for Re m ¼ 2388, a phenomenon reported before. 29 …”

Section: B Transition Of Steady Flowmentioning

confidence: 99%

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An experimental study of transitional pulsatile pipe flow

et al. 2012

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The transitional regime of a sinusoidal pulsatile flow in a straight, rigid pipe is investigated using particle image velocimetry. The main aim is to investigate how the critical Reynolds number is affected by different pulsatile conditions, expressed as the Womersley number and the oscillatory Reynolds number. The transition occurs in the region of Re ¼ 2250-3000 and is characterized by an increasing number of isolated turbulence structures. Based on velocity fields and flow visualizations, these structures can be identified as puffs, similar to those observed in steady flow transition. Measurements at different Womersley numbers yield similar transition behavior, indicating that pulsatile effects do not play a role in the regime that is investigated. Variations of the oscillatory Reynolds number also appear to have little effect, so that the transition here seems to be determined only by the mean Reynolds number. For larger mean Reynolds numbers, a second regime is observed: here, the flow remains turbulent throughout the cycle. The turbulence intensity varies during the cycle, but has a phase shift with respect to the mean flow component. This is caused by a growth of kinetic energy during the decelerating part and a decay during the accelerating part of the cycle. Flow visualization experiments reveal that the flow develops localized turbulence at several random axial positions. The structures quickly grow to fill the entire pipe in the decelerating phase and (partially) decay during the accelerating phase.

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“…It is seen that the velocity pro¦les at L/d = 65 and 200 (L = 1300 and 4000 mm) are fully turbulent, whereas the velocity pro¦le at L/d = 43.5 (L = 870 mm) exhibits a characteristic §at part in the §ow core indicative of the fact that the channel §ow in the latter case was not fully turbulent yet. [20] is given in Fig. 9b.…”

Section: Turbulent Jetmentioning

confidence: 99%