Turbulent fluctuations in the viscous wall region for Newtonian and drag reducing fluids

Hanratty, Thomas J.; Chorn, Larry; Hatziavramidis, Dimitrios T.

doi:10.1063/1.861719

Cited by 36 publications

(14 citation statements)

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“…However, for thin films the shear stress spectra show a local maximum at a frequency of 40 Hz. This corresponds roughly to what would be expected for the frequency of gas phase shear stress fluctuations (Hanratty et al, 1977). The wall shear stress tracings indicate no clear transition from laminar to turbulent flow.…”

Section: Page 2072supporting

confidence: 82%

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Effect of air shear on gas absorption by a liquid film

McCready

Hanratty

1985

AIChE Journal

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Gas Absorption by a Liquid FilmRates of oxygen absorption from turbulent air by a concurrently flowing liquid film were measured in an enclosed 2.54 cm x 30.5 cm rectangular channel. The effect of liquid viscosity is varied by using water and a water-glycerine solution. The results are interpreted by arguing that flow fluctuations in the liquid that control mass transfer are associated with waves of small wavelength at the interface. SCOPEGas absorption rates of a liquid layer are greatly enhanced by the presence of interfacial shear. Mass transfer coefficients for concurrent gas-liquid flows can be several times larger than those for liquid films that are freely falling down a vertical or inclined wall. The reasons for this are not completely understood. This paper presents results for oxygen absorption under carefully controlled conditions with the goal of investigating the role of an air flow in enhancing transfer rates. Particular insights were gained by varying the liquid viscosity and by accompanying the absorption measurements with measurements of wave properties, interfacial stress, and liquid phase turbulence.Our work was motivated to a large extent by a previous study made by Henstock and Hanratty (1979) in this laboratory. From experiments with water films, they correlated absorption results for a freely falling film (zero gas flow) with the equation K' = 0.0077m"/2 SC-"'.(1)Here K' and m+ are the mass transfer coefficient and the film height, made dimensionless with the friction velocity and the kinematic viscosity, and Sc is the Schmidt number. The rate expression for nonzero gas flow is, in general, quite different from Eq. 1. However, Henstock and Hanratty (Eq. 43 in the cited paper) suggested that at high ratios of the gas to liquid flow rate gas shear controlled mass transfer; the rate then is given by a relation of the same form as Eq. 1 for air and water flowing concurrently downward:K' = 0.0216 mtl" SC 'I2.(2) The present experiments, which are an extension of preliminary work reported by Henstock and Hanratty, allow for the study of oxygen absorption under conditions in which gas shear is completely controlling. They reveal a behavior quite different from Eq. 2. Henstock and Hanratty (1979) argued that turbulence in the liquid controlled mass transfer. Such an interpretation cannot explain the observed effect of liquid flow rate and, in particular, of liquid viscosity on the absorption rate. A more fruitful approach is to relate mass transfer to system variables through their effect on wave properties. A promising theoretical explanation of the effect of waves is that they induce spatial variations of interfacial drag that agitate the liquid close to the interface. CONCLUSIONS AND SIGNIFICANCE

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Section: Page 2072supporting

confidence: 82%

“…Gas phase turbulence is expected to agitate the fluid near the interface, in a manner indicated in Figure 1 length and frequency (Hanratty et al, 1977) given by w1 = 2oo7rV.,2/YG,…”

Section: Discussionmentioning

confidence: 99%

Effect of air shear on gas absorption by a liquid film

McCready

Hanratty

1985

AIChE Journal

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“…15. A possible explanation is that errors are introduced by the assumption of _U (Hatziavramidis 1978;Hanratty et al 1977) to suggest that the high frequency part of the streamwise velocity spectrum in the viscous sub-layer is given by solution of the linear x-momentum equation. A simplified version of this, analogous to (9) Values of W,(n) calculated from (12) using the W~(n) measurements in the viscous sub-layer are shown in Fig.…”

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confidence: 99%

Measurements of turbulent flow in a channel at low Reynolds numbers

Niederschulte

Adrian

Hanratty

1990

Experiments in Fluids

107

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Normal and streamwise components of the velocity fields of turbulent flow in a channel at low Reynolds numbers have been measured with laser-Doppler techniques. The experiments duplicate the conditions used in current direct numerical simulations of channel flow, and good, but not exact, agreement is found for singlepoint moments through fourth order. In order to eliminate LDV velocity bias and to measure velocity spectra, the mean time interval between LDV signals was adjusted to be much smaller than the smallest turbulence time scale. Spectra of the streamwise and normal components of velocity at locations spanning the channel are presented. I IntroductionThis paper presents measurements, made with a two-component laser-Doppler velocimeter, of the streamwise and normal velocity fields for turbulent flow in a rectangular channel. They were obtained at low velocites, so that the Reynolds number, based on the half channel height and the bulk velocity, was 2,777 or 2,457, and the dimensionless half width of the channel was H + = 178.6 or H + = 158.5, respectively. The motivation for this work was to examine the accuracy of the direct numerical simulation of three dimensional, time dependent turbulent flow in a channel at Re~ = 2,800 by Kim et al. (1987) and to obtain new measurements of the power spectral densities of both streamwise and normal turbulent velocity components.The study reported in this paper is part of a Ph.D. thesis by M. Niederschulte (1989). Measurements were made in fully developed flow 200 channel heights downstream from the entrance of a 5.08 x 61 cm rectangular channel by using a two-component laser Doppler velocimeter. Certain aspects of the LDV and the experimental procedure were tailored to the demands of this flow and make this experiment unique. Firstly, the optics were designed to permit accurate measurements at distances as close to the wall as y+ =0.6 (0.16 ram) with spatial resolution better than 0.035 mm in the direction normal to the wall. This was accomplished by using a threebeam LDV of the type described by Adrian (1975), combined with 6.27 : 1 expansion of the laser beams, as described in Buckles et al. (1984). Secondly, the fluid and the scattering medium in the fluid were also managed carefully to avoid the uncertainties associated with LDV velocity bias, and to produce data whose rate was large enough to permit measurement of the power spectra of the relatively low turbulence intensity flow. Carefully cleaned water was seeded with 808 nm polystyrene particles having a specific gravity of 1.05 and standard distribution of 0.5 %. The concentration of this very uniform scattering medium was chosen, in accord with the discussion in Adrian (1983), to be large enough to yield time intervals between particle arrivals that were smaller than the smallest turbulence time scale, but not so small as to create ambiguity (or "phase") noise. On average, the mean separation between particles in the streamwise direction was less than 0.2 ram. The resulting signal was a nearly continuous repre...

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“…• The power spectrum densities for the longitudinal velocity component for Newtonian and drag-reducing fluids are very close when normalized with wall parameters [9]. • Concurrently, an increase of the size of the macrostructures was observed in the transverse and the longitudinal directions.…”

Section: Introductionmentioning

confidence: 80%

“…The mean values of turbulence intensities obtained for water, [17] or 0.34 and 0.145 from [18] or 0.35 and 0.135 from [9]). However, the turbulence intensities measured for the transverse velocity component at the wall are still lower than those obtained from the DNS calculations (e.g.…”

Section: Power Spectramentioning

confidence: 99%