Transient velocity profiles and drag reduction due to air-filled superhydrophobic grooves

2020 ◽  
Vol 61 (11) ◽  
Author(s):  
Atsuhide Kitagawa ◽  
Yuriko Shiomi ◽  
Yuichi Murai ◽  
Petr Denissenko
Keyword(s):  
Drag Reduction ◽  
Velocity Profiles ◽  
Transient Velocity

Drag Reduction and Velocity Profiles Distribution of Crude Oil Flow in Spiral Pipes

2015 ◽  
Vol 9 (1) ◽  
pp. 1 ◽  
Author(s):  
Yanuar Yanuar ◽  
Kurniawan T. Waskito ◽  
Gunawan Gunawan ◽  
Budiarso Budiarso
Keyword(s):  
Drag Reduction ◽  
Crude Oil ◽  
Velocity Profiles ◽  
Oil Flow

Velocity Profiles During Drag Reduction

1969 ◽  
pp. 233-250 ◽  
Author(s):  
G. K. Patterson ◽  
G. L. Florez
Keyword(s):  
Drag Reduction ◽  
Velocity Profiles

Effects of Spatial Resolution and Box Size on Numerical Solutions of Turbulent Flows

2005 ◽  
Author(s):  
Dongmei Zhou ◽  
Kenneth S. Ball
Keyword(s):  
Drag Reduction ◽  
Channel Flow ◽  
Spatial Resolution ◽  
Numerical Solutions ◽  
Velocity Profiles ◽  
Wall Region ◽  
Computational Domain ◽  
Mean Velocity ◽  
Significant Difference ◽  
Near Wall

This paper has two objectives, (1) to examine the effects of spatial resolution, (2) to examine the effects of computational box size, upon turbulence statistics and the amount of drag reduction with and without the control scheme of wall oscillation. Direct numerical simulation (DNS) of the fully developed turbulent channel flow was performed at Reynolds number of 200 based on the wall-shear velocity and the channel half-width by using spectral methods. For the first objective, four different grids were applied to the same computational domain and the biggest impact was observed on the logarithmic law of mean velocity profiles and on the amount of drag reduction with 28.3% for the coarsest mesh and 35.4% for the finest mesh. Other turbulence features such as RMS velocity fluctuations, RMS vorticity fluctuations, and bursting events were either overpredicted or underpredicted through coarse grids. For the second objective, two different minimal channels and one natural full channel were studied and 3% drag reduction difference was observed between the smallest minimal channel of 39.1% and the natural full channel of 36.2%. In the near-wall region, however, the minimal channel flow did not exhibit significant difference in the mean velocity profiles and other lower-order statistics. Finally, from this systematical study, it showed that the accuracy of DNS depends more on the spanwise resolution, and it also confirmed that a minimal channel model is able to catch key structures of turbulence in the near-wall region but is much less expensive.

Frictional Resistance of Flat Plates in Dilute Polymer Solutions

1973 ◽  
Vol 17 (04) ◽  
pp. 227-240
Author(s):  
L. Landweber ◽  
M. Poreh
Keyword(s):  
Drag Reduction ◽  
Frictional Resistance ◽  
Velocity Profiles ◽  
Experimental Result ◽  
Flat Plates ◽  
Law Of The Wall ◽  
Family Of Curves ◽  
Maximum Drag Reduction ◽  
The Law ◽  
Two Parameter

For a flat plate moving in a dilute polymer solution, effects on boundary-layer characteristics, shear stress, drag reduction and maximum drag reduction are considered for polymers which satisfy the Meyer-Elata law. Results are derived from a model in which the velocity profiles satisfy the law-of-the-wall and a velocity-defect law, and the polymer has no effect in the range in which the latter law is valid. It is also assumed that the polymer affects the law of variation of the mixing length, and a family of velocity profiles representing this effect is adopted. This model then yields a curve of maximum drag reduction as well as a two-parameter family of curves of drag reduction, consequences of the nonoverlapping or overlapping of the two velocity-profile laws. The results are compared with those of Granville for drag reduction, and with the predicted curve of Virk-Granville and an experimental result of Levy and Davis for maximum drag reduction.

The Noise-Producing Characteristics of Highly Loaded, Valveless, Pulse Combustors

1988 ◽  
Vol 110 (2) ◽  
pp. 238-245 ◽  
Author(s):  
J. A. C. Kentfield
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Noise Suppression ◽  
Analytical Data ◽  
Velocity Profiles ◽  
Noise Generation ◽  
Noise Levels ◽  
Transient Velocity ◽  
Inherent Problem ◽  
Frequency Pulse

An inherent problem of pulsating combustors is noise generation and the difficulty of predicting noise levels. Analytical data are presented which illustrate the transient velocity profiles prevailing at the open ends of the inlets and tailpipes of valveless pulse combustors. A comparison is made of measured sound pressure level spectra at these locations with corresponding predicted transient velocity profiles. It is shown that there is a correlation of the main characteristics of the noise spectra and velocity profiles. Consideration is also given to the problems of muffling valveless pulse combustors and the potential, from the noise suppression viewpoint, of twin-coupled units and relatively high frequency pulse combustors featuring multiple inlet passages. An indication is also given of how it may be possible to operate clusters, or arrays, of pulse combustors firing sequentially.

High-fidelity measurements in channel flow with polymer wall injection

2018 ◽  
Vol 859 ◽  
pp. 851-886 ◽  
Author(s):  
John R. Elsnab ◽  
Jason P. Monty ◽  
Christopher M. White ◽  
Manoochehr M. Koochesfahani ◽  
Joseph C. Klewicki
Keyword(s):  
Shear Stress ◽  
Drag Reduction ◽  
Channel Flow ◽  
Polymer Concentration ◽  
Streamwise Velocity ◽  
Velocity Profiles ◽  
Order Structure ◽  
Dynamical Structure ◽  
Molecular Tagging Velocimetry ◽  
The Mean

Streamwise velocity profiles and their wall-normal derivatives were used to investigate the properties of turbulent channel flow in the low polymer drag reduction$(DR)$regime ($DR=6.5\,\%$to$26\,\%$), as realized via polymer injection at the channel surface. Streamwise velocity data were obtained over a friction Reynolds number ranging from$650$to$1800$using the single-velocity-component version of molecular tagging velocimetry (1c-MTV). This adaptation of the MTV technique has the ability to accurately capture instantaneous profiles at very high spatial resolution (${\gtrsim}850$data points per wall-normal profile), and thus generate well-resolved derivative information as well. Owing to this ability, the present study is able to build upon and extend the recent numerical simulation analysis of Whiteet al. (J. Fluid Mech., vol. 834, 2018, pp. 409–433) that examined the mean dynamical structure of polymer drag-reduced channel flow at friction Reynolds numbers up to$1000$. Consistently, the present mean velocity profiles indicate that the extent of the logarithmic region diminishes with increasing polymer concentration, while statistically significant increases in the logarithmic profile slope begin to occur for drag reductions less than$15\,\%$. Profiles of the r.m.s. streamwise velocity indicate that the maximum moves farther from the wall and increases in magnitude with reductions in drag. Similarly, with increasing drag reduction, the profile of the combined Reynolds and polymer shear stress exhibits a decrease in its maximum value that also moves farther from the wall. Correlations are presented that estimate the location and value of the maximum r.m.s. streamwise velocity and combined Reynolds and polymer shear stress. Over the range of$DR$investigated, these effects consistently exhibit approximately linear trends as a function of$DR$. The present measurements allow reconstruction of the mean momentum balance (MMB) for channel flow, which provides further insights regarding the physics described in the study by Whiteet al. In particular, the present findings support a physical scenario in which the self-similar properties on the inertial domain identified from the leading-order structure of the MMB begin to detectably and continuously vary for drag reductions less than$10\,\%$.

On the scaling of air layer drag reduction

2013 ◽  
Vol 717 ◽  
pp. 484-513 ◽  
Author(s):  
Brian R. Elbing ◽  
Simo Mäkiharju ◽  
Andrew Wiggins ◽  
Marc Perlin ◽  
David R. Dowling ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Void Fraction ◽  
Free Stream ◽  
Boundary Layer Separation ◽  
Velocity Profiles ◽  
Test Model ◽  
Interfacial Velocity ◽  
Local Skin ◽  
Air Layer Drag Reduction

AbstractAir-induced drag reduction was investigated on a 12.9 m long flat plate test model at a free stream speed of $6. 3~\mathrm{m} ~{\mathrm{s} }^{- 1} $. Measurements of the local skin friction, phase velocity profiles (liquid and gas) and void fraction profiles were acquired at downstream distances to 11.5 m, which yielded downstream-distance-based Reynolds numbers above 80 million. Air was injected within the boundary layer behind a 13 mm backward facing step (BFS) while the incoming boundary layer was perturbed with vortex generators in various configurations immediately upstream of the BFS. Measurements confirmed that air layer drag reduction (ALDR) is sensitive to upstream disturbances, but a clean boundary layer separation line (i.e. the BFS) reduces such sensitivity. Empirical scaling of the experimental data was investigated for: (a) the critical air flux required to establish ALDR; (b) void fraction profiles; and (c) the interfacial velocity profiles. A scaling of the critical air flux for ALDR was developed from balancing shear-induced lift forces and buoyancy forces on a single bubble within a shear flow. The resulting scaling successfully collapses ALDR results from the current and past studies over a range of flow conditions and test model configurations. The interfacial velocity and void fraction profiles were acquired and scaled within the bubble drag reduction (BDR), ALDR and transitional ALDR regimes. The BDR interfacial velocity profile revealed that there was slip between phases. The ALDR results showed that the air layer thickness was nominally three-quarters of the total volumetric flux (per unit span) of air injected divided by the free stream speed. Furthermore, the air layer had an average void fraction of 0.75 and a velocity of approximately 0.2 times the free stream speed. Beyond the air layer was a bubbly mixture that scaled in a similar fashion to the BDR results. Transitional ALDR results indicate that this regime was comprised of intermittent generation and subsequent fragmentation of an air layer, with the resulting drag reduction determined by the fraction of time that an air layer was present.

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