Studies of the Wall Shear Stress in a Turbulent Pulsating Pipe Flow

Mao, Zugang; Hanratty, Thomas J.

doi:10.21236/ada146772

Cited by 8 publications

(8 citation statements)

References 16 publications

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“…This has similar physical basis to the parameters ω + and l + used by Mao & Hanratty (1986) and Tardu et al (1994), respectively, for periodic flows. As mentioned at the beginning of this section, the delay associated with the propagation of turbulence across the flow is the most pronounced of the delays which have been identified in the ramp-type flows under consideration here.…”

Section: The Post-transient Responsementioning

confidence: 69%

“…This parameter provides a measure of how far the viscous Stokes layer extends into the inner region of a turbulent flow. The parameter ω + (= ων/U 2 τ ) used by Mao & Hanratty (1986) is directly related to the Stokes-Reynolds number through ω + = 2/l +2 s . It will be seen later in the present paper that the diffusion of turbulence and the spread of the viscous Stokes layer are both important features of non-periodic transient turbulent flow.…”

Section: Periodic Pulsating Flowsmentioning

confidence: 99%

“…In that case, the Stokes sublayer 2ν/ω is used. This provides a measure of the extent to which the wall constraint extends during a cycle of the flow variation (Mao &Hanratty 1986 andTardu et al 1994).…”

Section: Turbulence Fieldmentioning

confidence: 99%

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A study of turbulence under conditions of transient flow in a pipe

Jackson

2000

J. Fluid Mech.

114

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A detailed investigation of fully developed transient flow in a pipe has been undertaken using water as the working fluid. Linearly increasing or decreasing excursions of flow rate were imposed between steady initial and final values. A three-beam, two-component laser Doppler anemometer was used to make simultaneous measurements of either axial and radial, or axial and circumferential, components of local velocity. Values of ensemble-averaged mean velocity, root-mean-square velocity fluctuation and turbulent shear stress were found from the measurements.Being the first really detailed study of ramp-type transient turbulent flow, the present investigation has yielded new information and valuable insight into certain fundamental aspects of turbulence dynamics. Some striking features are evident in the response of the turbulence field to the imposed excursions of flow rate. Three different delays have been identified: a delay in the response of turbulence production; a delay in turbulence energy redistribution among its three components; and a delay associated with the propagation of turbulence radially. The last of these is the most pronounced under the conditions of the present study. A dimensionless delay parameter τ+[= √2τUτ0/D] is proposed to describe it. The first response of turbulence is found to occur in the region near the wall where turbulence production peaks. The axial component of turbulence responds earlier than the other two components and builds up faster. The response propagates towards the centre of the pipe through the action of turbulent diffusion at a speed which depends on the Reynolds number at the start of the excursion. In the core region, the three components of turbulence energy respond in a similar manner. Turbulence intensity is reduced in the case of accelerating flow and increased in decelerating flow. This is mainly as a result of the delayed response of turbulence. A dimensionless ramp rate parameter γ[= (dUb/dt) (1/Ub0)(D/Uτ0] is proposed, which determines the extent to which the turbulence energy differs from that of pseudo-steady flow as a result of the delay in the propagation of turbulence.

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Section: The Post-transient Responsementioning

confidence: 69%

Section: Periodic Pulsating Flowsmentioning

confidence: 99%

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A study of turbulence under conditions of transient flow in a pipe

Jackson

2000

J. Fluid Mech.

114

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“…The best documented quantity is the modulation of the wall shear stress fluctuations 7'7' Mao & Hanratty 1986;Finnicum & Hanratty 1988;Tardu & Binder 1993). These measurements show that the amplitude and phase shift of the fundamental mode of vary considerably with the forcing frequency.…”

Section: _ Imentioning

confidence: 99%

Turbulent channel flow with large-amplitude velocity oscillations

1994

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Measurements in turbulent channel flow with forced oscillations covering a wide range of frequencies (ω+ = 0.03–0.0005) and amplitudes (10–70% of centreline velocity) are presented and discussed. Phase averages of the velocity <u> across the flow, and of the wall shear stress <τ>, as well as the turbulent fluctuations <u′u′> and <t′t′> are obtained with LDA and hot-film techniques. The time-mean quantities, except u’2, are only slightly affected by the imposed oscillations whatever their frequency and amplitude. It is shown that the appropriate similarity parameter for the oscillating quantities ũ and ĩ is the non-dimensional Stokes length l+s (or the frequency ω+ = 2/l+2s). In the regime of high-frequency forcing (l+s < 10) the oscillating flow ũ and ĩ are governed by purely viscous shear forces although the time-mean flow is fully turbulent. This behaviour may be explained by the physical significance of l+s. At lower frequency l+s 10, the oscillating flow is influenced by the turbulence, in particular the amplitude of ĩ increases with respect to the Stokes amplitude and becomes proportional to l+s. The relative amplitude of <u′u′> and <t′t′> decreases sharply with increasing forcing frequency once l+s < 25. This decay of the turbulence response is faster for the wall shear stress. For forcing frequencies such that l+s > 12, <u′u′> and <t′t′> lag behind <u> and <τ> by respectively about 75 and 130 viscous time units. These lags decrease by a factor 2 at higher forcing frequencies. It is shown that in the log layer, the turbulence modulation diffuses away from the wall with a diffusivity equal to that of the time-mean turbulence. The imposed oscillations are felt down to the small scales of the turbulence as may be evidenced from the cyclic modulation of the Taylor microscale, the skewness and the flatness factors of δu′/δt. The modulations of the skewness and the flatness go through a maximum around l+s = 12.

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“…with erW = limg4 @,(y), as can be shown by differentiating (2). This paper presents the results of experiments with a fully developed pipe flow in which I Q, I and @ , w are related to Id$/dx) (Mao 1984). The experiments were conducted at high enough frequencies that fluid inertia is dominant over most of the flow field and the profile of the disturbance velocity is flat over the central regions of the pipe.…”

Section: Introductionmentioning

confidence: 99%

Studies of the wall shear stress in a turbulent pulsating pipe flow

Mao

Hanratty

1986

J. Fluid Mech.

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Measurements are presented of the time variation of the wall shear stress caused by the imposition of a sinusoidal oscillation on a turbulent pipe flow. The amplitude of the oscillation is small enough that a linear response is obtained and the dimensionless frequency, ω+ = ων/u*2, is large compared with that studied by most previous investigators. The most striking feature of the results is a relaxation effect, similar to that observed for flow over a wavy surface, whereby the phase angle characterizing the temporal variation of the wall shear stress undergoes a sharp change over a rather narrow range of ω+. At ω+ larger than the median frequency of the turbulence there appears to be an interaction between the imposed flow oscillation and the turbulence fluctuations in the viscous sublayer, which is not described by present theories of turbulence.

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Studies of the Wall Shear Stress in a Turbulent Pulsating Pipe Flow

Cited by 8 publications

References 16 publications

A study of turbulence under conditions of transient flow in a pipe

A study of turbulence under conditions of transient flow in a pipe

Turbulent channel flow with large-amplitude velocity oscillations

Studies of the wall shear stress in a turbulent pulsating pipe flow

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