Pulsating pipe flow with large-amplitude oscillations in the very high frequency regime. Part 2. Phase-averaged analysis

2015 ◽  
Vol 766 ◽  
pp. 272-296 ◽  
Author(s):  
M. Manna ◽  
A. Vacca ◽  
R. Verzicco
Keyword(s):  
Pipe Flow ◽  
Experimental Studies ◽  
Turbulence Models ◽  
Turbulent Pipe Flow ◽  
Very High Frequency ◽  
Frequency Regime ◽  
Order Of Magnitude ◽  
Flow Cycle ◽  
Mean Current

AbstractThis paper is the follow-up of a previous study (Manna, Vacca & Verzicco,J. Fluid Mech., vol. 700, 2012, pp. 246–282) that numerically investigated the effects of a harmonic volume forcing on the turbulent pipe flow at a bulk Reynolds number of$\simeq 5900$. There, the investigation was focused on the time- and space-averaged statistics of the first- and second-order moments of the velocity, the vorticity fluctuations and the Reynolds stress budgets in order to study the changes induced on the mean current by the oscillating component. The amplitude of the latter was used as a parameter for the analysis. However, as the flow is inherently unsteady, the phase-averaged statistics are also of interest, and this is the motivation and subject of the present study. Here, we show the variability of the above quantities during different phases of the flow cycle and how they are affected by the amplitude of the oscillation. It is observed that when the ratio of the oscillating to the time-constant velocity component is of the order of one (${\it\beta}\simeq O(1)$), the phase-averaged profiles are appreciably influenced by the pulsation, although only small deviations of the time-averaged counterparts have been documented. In contrast, when that ratio is increased by one order of magnitude (${\it\beta}\simeq O(10)$) the phase- and cycle-averaged quantities differ considerably, especially during the decelerating part of the cycle. In more detail, the amplitude and the phase of all turbulence statistics show significant variations with${\it\beta}$. This variability has important implications in the dynamics and modelling of these flows. Since the data have been obtained by direct numerical simulations and validated by comparisons with experimental studies, the results could be used for validation of codes, testing of turbulence models or measurement procedures.

Pulsating pipe flow with large-amplitude oscillations in the very high frequency regime. Part 1. Time-averaged analysis

2012 ◽  
Vol 700 ◽  
pp. 246-282 ◽  
Author(s):  
M. Manna ◽  
A. Vacca ◽  
R. Verzicco
Keyword(s):  
Pipe Flow ◽  
Oscillatory Flow ◽  
Turbulent Pipe Flow ◽  
Bulk Velocity ◽  
Subsequent Paper ◽  
Very High Frequency ◽  
Harmonic Forcing ◽  
Frequency Regime ◽  
Pipe Radius ◽  
The Mean

AbstractThis paper numerically investigates the effects of a harmonic volume forcing of prescribed frequency on the turbulent pipe flow at a Reynolds number, based on bulk velocity and pipe diameter, of 5900. The thickness of the Stokes layer, resulting from the oscillatory flow component, is a small fraction of the pipe radius and therefore the associated vorticity is confined within a few wall units. The harmonic forcing term is prescribed so that the ratio of the oscillating to the mean bulk velocity ($\ensuremath{\beta} $) ranges between 1 and 10.6. In all cases the oscillatory flow obeys the Stokes analytical velocity distribution while remarkable changes in the current component are observed. At intermediate values $\ensuremath{\beta} = 5$, a relaminarization process occurs, while for $\ensuremath{\beta} = 10. 6$, turbulence is affected so much by the harmonic forcing that the near-wall coherent structures, although not fully suppressed, are substantially weakened. The present study focuses on the analysis of the time- and space-averaged statistics of the first- and second-order moments, vorticity fluctuations and Reynolds stress budgets. Since the flow is unsteady not only locally but also in its space-averaged dynamics, it can be analysed using phase-averaged and time-averaged statistics. While the former gives information about the statistics of the fluctuations about the mean, the latter, postponed to a subsequent paper, shows how the mean is affected by the fluctuations. Clearly, the two phenomena are connected and both of them deserve investigation.

scholarly journals The effect of pulsation frequency on transition in pulsatile pipe flow

2018 ◽  
Vol 857 ◽  
pp. 937-951 ◽  
Author(s):  
Duo Xu ◽  
Marc Avila
Keyword(s):  
Pipe Flow ◽  
Experimental Studies ◽  
Quantitative Agreement ◽  
Transition To Turbulence ◽  
Pulsation Frequency ◽  
Pipe Length ◽  
Pulsation Amplitude ◽  
Frequency Regime ◽  
Pulsatile Flows ◽  
The Stability

Pulsatile flows are common in nature and in applications, but their stability and transition to turbulence are still poorly understood. Even in the simple case of pipe flow subject to harmonic pulsation, there is no consensus among experimental studies on whether pulsation delays or enhances transition. We here report direct numerical simulations of pulsatile pipe flow at low pulsation amplitude$A\leqslant 0.4$. We use a spatially localized impulsive disturbance to generate a single turbulent puff and track its dynamics as it travels downstream. The computed relaminarization statistics are in quantitative agreement with the experiments of Xuet al. (J. Fluid Mech., vol. 831, 2017, pp. 418–432) and support the conclusion that increasing the pulsation amplitude and lowering the frequency enhance the stability of the flow. In the high-frequency regime, the behaviour of steady pipe flow is recovered. In addition, we show that, when the pipe length does not permit the observation of a full cycle, a reduction of the transition threshold is observed. We obtain an equation quantifying this effect and compare it favourably with the measurements of Stettler & Hussain (J. Fluid Mech., vol. 170, 1986, pp. 169–197). Our results resolve previous discrepancies, which are due to different pipe lengths, perturbation methods and criteria chosen to quantify transition in experiments.

Experimental Studies of Small Air Bubble Motion in Turbulent Pipe Flow

2010 ◽  
Author(s):  
Olesya Zhukovskaya ◽  
Ronald J. Hugo
Keyword(s):  
Reynolds Number ◽  
Velocity Profile ◽  
Pipe Flow ◽  
Experimental Studies ◽  
Continuous Phase ◽  
Turbulent Pipe Flow ◽  
Single Bubble ◽  
Bubble Flow ◽  
Horizontal Pipe ◽  
Air Bubble

The main objective of this research is to collect statistical information concerning momentum phase coupling between the continuous phase and a single air bubble in turbulent flow in a horizontal pipe, and to develop data that can be used for the verification of numerical modeling efforts. In comparison with vertical pipe bubble flow, horizontal bubble flow has received less attention, especially from the experimental side. Thus, an experimental investigation of bubble behaviour in a horizontal square pipe was performed. Tracking of a single bubble released in water flow in a 56.8 mm × 56.8 mm square pipe was performed to provide a basis for characterizing the behaviour of the single bubble in turbulent pipe flow. A Shack Hartman Wavefront Sensor and a High Speed Video Camera were used to collect images at various points downstream from the bubble injection point, providing information on bubble size, velocity, and spatial location as a function of Reynolds number. Velocity profile information of the continuous phase was collected using Particle Image Velocimetry (PIV) in order to perform a complete characterization of the flow. The data collected using PIV coupled with the analysis of the three-dimensional trajectory of a single bubble provides information about parameters such as a gas slippage velocity with the fluid phase and bubble distribution as a function of both Reynolds number and mean velocity profile.

scholarly journals Experimental techniques against RANS method in a fully-developed turbulent pipe flow

2021 ◽  
Author(s):  
Gabriela Belen Lopez-Santana ◽  
Andrew Kennaugh ◽  
Amir Keshmiri
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Pipe Flow ◽  
Turbulence Models ◽  
Turbulent Pipe Flow ◽  
Experimental Techniques ◽  
Mean Velocity ◽  
Experimental Apparatus ◽  
Wall Shear ◽  
The University

Turbulence has been studied by scientists and engineers for decades as it appears in the majority of the fluids existent in nature and in engineering applications and because turbulent flow and its underlying behaviour are tremendously complex. The University of Manchester is widely viewed as the birthplace of turbulence due to the pioneering work of one of its prominent academics, Professor Osborne Reynolds (1842-1912). Building on this legacy, a classical experimental apparatus has been used in this paper to study a turbulent pipe flow with the aim of measuring the mean velocity field and wall shear stress using four experimental techniques, all developed in the 20th century, namely static pressure drop; mean square signals measured from a hot-wire; Preston tube; and the ‘Clauser Plot’. The experimental results have then been compared against those obtained using Computational Fluid Dynamics (CFD), utilising different two-equation turbulence models. The present work highlights the discrepancies evident in obtaining the value of the wall shear stress in each method. In addition, the scopes and limitations of each technique are discussed in detail, highlighting the clear evolution of turbulence study tools over the last 100 years.

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