Transient dynamics of accelerating turbulent pipe flow

Guerrero, Byron; Lambert, Martin F.; Chin, Rey

doi:10.1017/jfm.2021.303

Cited by 17 publications

(43 citation statements)

References 36 publications

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“…First, it is noteworthy that the turbulent forces start decaying within the viscous sublayer as soon as the flow is decelerated. This contrasts with the features exhibited by accelerating flows during the same period (see Guerrero et al 2021), where a frozen behaviour in the turbulent forces within this early period was observed. In the same figure it is skin friction coefficient (C f ) attains a maximum.…”

Section: Time Evolution Of the Turbulent Inertia And Viscous Forcecontrasting

confidence: 67%

“…However, during this period, the mean velocity profile presents its most relevant changes within the buffer and overlap regions (10 y +1 100). It is also noted that, during this stage, the wake region exhibits a marginal change, indicating that decelerating flows possibly have a nearly 'quiescent' behaviour at the core region during the three first transitional stages, similar to their accelerating counterpart (Guerrero et al 2021). At the end of this stage, the mean velocity profile at the viscous sublayer starts converging, and its characteristic linear behaviour is recovered.…”

Section: Time Response Of the Mean Velocity Profilementioning

confidence: 75%

“…the transition mechanism and timings of the different transitional stages are unclear, possibly due to the masking effect by the existing flow structures at the beginning of the transient or due to the step-down size chosen'. In contrast with the studies associated with the behaviour of rapidly accelerating flows (see Greenblatt & Moss 2004;He & Seddighi 2013;Guerrero et al 2021), the different transient stages undergone by a rapidly decelerating flow are still elusive.…”

Section: Motivationmentioning

confidence: 91%

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Transient behaviour of decelerating turbulent pipe flows

2023

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This investigation characterises the time response and the transient turbulence dynamics undergone by rapidly decelerating turbulent pipe flows. A series of direct numerical simulations of decelerating flows between two steady Reynolds numbers were conducted for this purpose. The statistical analyses reveal that rapidly decelerating turbulent flows undergo four coherent, unambiguous transitional stages: inertial (stage I), a dramatic change of sign in the viscous force associated with the decay of the viscous shear stress at the wall together with a mild turbulence decay in the viscous sublayer; friction recovery (stage II), a recovery in viscous force and progressive decay in the turbulent inertia at the near-wall region; turbulence decay (stage III), a balanced decay in both turbulent inertia and viscous force at the near-wall and overlap regions; core relaxation (stage IV), slow turbulence decay at the core region. The FIK identity derived by Fukagata, Iwamoto and Kasagi (Phys. Fluids, vol. 14, 2002, L73–L76) was used to understand further how the flow dynamics influence the time response of the skin friction coefficient ( $C_f$ ). The results show that although $C_f$ plateaus during the fourth stage, the turbulent contribution keeps decaying, undershoots and finally recovers to attain its final steady value. The time evolution of the azimuthal vorticity ( $\omega _\theta$ ) flux reveals that as the flow is decelerated, a layer of negative $\omega _\theta$ is produced at the wall during the flow excursion. As time progresses, this negative vorticity propagates in the wall-normal direction, attenuating the pre-existing vorticity and producing a decay in the turbulence levels.

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Section: Time Evolution Of the Turbulent Inertia And Viscous Forcecontrasting

confidence: 67%

Section: Time Response Of the Mean Velocity Profilementioning

confidence: 75%

Section: Motivationmentioning

confidence: 91%

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Transient behaviour of decelerating turbulent pipe flows

2023

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“…Then the regime becomes fully turbulent, after having contaminated with the new turbulence properties the whole of the boundary layer thickness. This interpretation has recently been further consolidated by DNS of Guerrero, Lambert & Chin (2021) ranging from low to moderate initial Reynolds numbers. He & Seddighi (2015) have examined the influence of the final-to-initial Reynolds number ratio on the temporal transition mechanism.…”

Section: Temporal Acceleration Of Turbulent Flowmentioning

confidence: 79%

Flat plate boundary layer accelerated by shock wave propagation

2022

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The flat plate transitional boundary layer response to the acceleration induced by the shock wave propagation is studied using large-eddy simulations. The steady boundary layer global behaviour is first investigated before focusing on the transient response of a turbulent region following the shock wave propagation. It is shown that the transient response of the turbulent region exhibits strong similarities with the spatial transition process to turbulence induced by free-stream turbulence, the so-called bypass transition. The boundary layer does not evolve gradually from the initial turbulence intensity to the final turbulence intensity but undergoes a temporal transition process composed of three distinct phases. These three different phases are comparable with the three stages of a bypass transition (i.e. buffeted laminar flow, transition and fully turbulent) because they are governed by the same physical processes. On the other hand, it is highlighted that this temporal response is identical to that described by He & Seddighi (J. Fluid Mech., vol. 715, 2013, pp. 60–102) during the study of an incompressible boundary layer undergoing an increase of mass flow rate. The boundary layer compression by the shock propagation does not contribute to any significant change in the turbulence dynamic after an unsteady acceleration.

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“…Jung & Kim (2017) investigated temporal acceleration in channel flow and found that at longer acceleration durations, transition occurs less clearly than was observed in cases of rapid acceleration. More recently, Guerrero, Lambert & Chin (2021) discovered a distinct inertial phase, which may occur before pre-transition in some strongly accelerated flows. This stage is described as being characterised by a rapid and substantial increment in the viscous forces within the viscous sublayer, together with the frozen existing turbulent eddies.…”

Section: Introductionmentioning

confidence: 99%

A spatially accelerating turbulent flow with longitudinally contracting walls

Falcone

2022

J. Fluid Mech.

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This paper describes a study of spatially accelerating turbulent flow based on the direct numerical simulation of a flow with longitudinally accelerating moving walls to create a relative acceleration between the fluid and the wall without inducing streamline curvature. The results show a broad similarity to those of previous investigations of spatial acceleration, albeit with some differences. A new interpretation has been proposed considering this spatially accelerating flow to be characterised by the formation of a new boundary layer superimposed on the pre-existing turbulent flow. This is followed by the transition of the flow in response to the development of this new boundary layer. This can be seen as an extension of the transition theory for temporally accelerating turbulent flows (He & Seddighi, J. Fluid Mech., vol. 715, 2013, pp. 60–102). The existing turbulent structures act as disturbances for the new boundary layer similar to the role of free-stream turbulence in bypass transition. This boundary layer modulates the pre-existing near-wall structures, amplifying and elongating the streaks. Some streaks eventually become unstable in a sinuous mechanism reminiscent of streak breakdown in near-wall turbulence, resulting in the formation localised turbulent spots which spread until the entire wall is covered in new turbulence. This interpretation naturally splits the flow into a new boundary layer region and a core (or free-stream) flow with interactions between the two dominating a significant length of the flow development and potentially offers a new explanation for the slow evolution of the turbulent stresses observed previously.

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Transient dynamics of accelerating turbulent pipe flow

Abstract: Abstract

Cited by 17 publications

References 36 publications

Transient behaviour of decelerating turbulent pipe flows

Transient behaviour of decelerating turbulent pipe flows

Flat plate boundary layer accelerated by shock wave propagation

A spatially accelerating turbulent flow with longitudinally contracting walls

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