Effect of bubble distribution on wall drag in turbulent channel flow

Jha, Narsing K.; Bhatt, Anubhav; Govardhan, Raghuraman N.

doi:10.1007/s00348-019-2773-7

Cited by 13 publications

(13 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Moreover, other types of background estimation, e.g. the minimum or standard deviation of the snapshot ensemble of I(x, y), could be used in equation (1)(2)(3). In the present work, however, we concentrate solely on I, due to its simple mathematical realization.…”

Section: Ratio Cut Methodsmentioning

confidence: 99%

“…Velocity-field measurement in the near-wall region of wallbounded turbulence is of fundamental importance in the study of drag reduction techniques that aim to reduce skin friction in transportation vehicles, by either passive [1,2] or active methods [3]. Most existing techniques employ the strategy of suppressing near-wall turbulent fluctuations by introducing favorable disturbances [4,5]: the evaluationg of drag reduction performance, as well as the examination of underlying physical mechanisms, therefore relies on a comprehensive knowledge of the characteristics of the near-wall flow field.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Ratio-cut background removal method and its application in near-wall PTV measurement of a turbulent boundary layer

Wang

Pan

Liu

et al. 2020

Meas. Sci. Technol.

View full text Add to dashboard Cite

Optical contamination due to wall reflection creates limitations for near-wall velocity field measurement via either particle image velocimetry (PIV) or particle tracking velocimetry (PTV). In this paper, a simple image pre-processing method, i.e. the ratio cut method, is proposed to deal with this problem. It is based on the ratio between the grayscale intensities of tracer particles and those of the laser-illuminated background, on which a direct minimum cut is applied on the basis of a non-dimensional threshold for background removal. To evaluate its performance in near-wall measurement, this ratio cut method, along with two other typical pre-processing methods, i.e. the minimum removal method and the proper orthogonal decomposition (POD) filtering method, are applied to particle images in the near-wall region of turbulent boundary layers over an opaque roughness wall (ORW), whose characteristic roughness height is small enough to be regarded as hydraulically smooth, but still gives rise to severe wall reflection. Results for a case involving a transparent smooth wall, which suffers less from wall reflection issues, and direct numerical simulation (DNS) data at a similar Reynolds number are employed as reference baselines for performance evaluation. The examination of pre-processed particle images, as well as the probability density function (PDF) of grayscale intensities, indicates that the ratio cut method is capable of eliminating time-dependent flare, reducing noise level, and retaining low-intensity particles in the ORW case. These features are almost completely absent in both the minimum removal method and the POD filtering method. In addition, PTV-obtained velocity statistics for an ORW, pre-processed by the ratio cut method, including data relating to fluctuating intensity and the PDF distribution of fluctuating velocity, are shown to be more consistent with those relating to baseline cases than data obtained by either of the the other two methods used for comparison. Moreover, evidence is also provided regarding the superiority and robustness of this approach, in terms of estimating the mean skin friction from the near-all mean velocity profile.

show abstract

Section: Ratio Cut Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ratio-cut background removal method and its application in near-wall PTV measurement of a turbulent boundary layer

Wang

Pan

Liu

et al. 2020

Meas. Sci. Technol.

View full text Add to dashboard Cite

show abstract

“…The present experiments were performed in a closed loop type fully developed horizontal turbulent channel flow facility developed by Jha et al (2019). The flow medium was tap water, and in order to vary the bubble coalescence rate, the concentration of salt in the tap water was systematically increased, and its effects at different Re and α, as mentioned in table 1, were studied.…”

Section: Experimental Set-upmentioning

confidence: 99%

Effects of salt concentration on top wall bubble injection in a turbulent channel flow: bubble dynamics and wall drag reduction

Biswas,

Govardhan

2024

Exp Fluids

Self Cite

View full text Add to dashboard Cite

Most applications related to bubble drag reduction (BDR) occur in contaminated environments where the presence of different surface active agents modify bubble coalescence and hence, affect flow drag. Although there have been studies on bubble drag modifications with salt/surfactant, the effects of systematic variation in salt/surfactant concentration on bubble dynamics and drag remain relatively unexplored. Driven by this motivation, in the present work, we experimentally investigate the effects of salt concentration on the bubble dynamics and drag modification in a fully developed horizontal turbulent channel flow for top wall bubble injection, over a wide range of salt concentrations (0< M <0.08, moles/liter), channel Reynolds number (22,500< Re <65,000), and injected bubble void fraction (0< α <0.16). The injected bubbles interact with the flow in the turbulent channel and as they move downstream reach an equilibrium state between the bubbly phase and the fully developed carrier phase that persists further downstream. The equilibrium state of the bubble dynamics is captured by high-speed visualizations and the corresponding drag is obtained from stream-wise pressure drop measurements within the channel. Increasing salt concentration levels is seen to lead to reduction in bubble coalescence and consequently in bubble size that modifies bubble deformability, migration, and distribution near the top wall, with the changes being dependent on the Re and α values. At low Re ≈ 22, 500, the addition of salt leads to a dramatic reduction in bubble sizes (∼ 100 microns)

show abstract

“…122 It seems that drag reduction of the mucus effect from the predator (Pacic barracuda) is better. Polymer additives that are inspired from mucus such as small amounts of high molecular weight polymers in water, 123 micellar surfactant systems, 79 bubbles, [124][125][126] coatings, 29,127 and even solid spheres 128 can reduce drag, which has important potential implications for reducing energy losses in pipelines and underwater vehicles. 17,18,129 In recent years, riblets have been extensively studied, and sh mucus and riblets of sh are considered to have a coupling effect on drag reduction, thus affecting the structure of the ow eld around the sh.…”

Section: Other Aquatic Animals-inspired Drag Reductionmentioning

confidence: 99%

“… 122 It seems that drag reduction of the mucus effect from the predator (Pacific barracuda) is better. Polymer additives that are inspired from mucus such as small amounts of high molecular weight polymers in water, 123 micellar surfactant systems, 79 bubbles, 124–126 coatings, 29,127 and even solid spheres 128 can reduce drag, which has important potential implications for reducing energy losses in pipelines and underwater vehicles. 17,18,129 …”

Section: Biological Prototypesmentioning

confidence: 99%

Thriving artificial underwater drag-reduction materials inspired from aquatic animals: progresses and challenges

et al. 2021

View full text Add to dashboard Cite

show abstract

Effect of bubble distribution on wall drag in turbulent channel flow

Cited by 13 publications

References 32 publications

Ratio-cut background removal method and its application in near-wall PTV measurement of a turbulent boundary layer

Ratio-cut background removal method and its application in near-wall PTV measurement of a turbulent boundary layer

Effects of salt concentration on top wall bubble injection in a turbulent channel flow: bubble dynamics and wall drag reduction

Thriving artificial underwater drag-reduction materials inspired from aquatic animals: progresses and challenges

Contact Info

Product

Resources

About