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An analysis of superhydrophobic turbulent drag reduction mechanisms using direct numerical simulation
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10.1063/1.3432514
/content/aip/journal/pof2/22/6/10.1063/1.3432514
http://aip.metastore.ingenta.com/content/aip/journal/pof2/22/6/10.1063/1.3432514

Figures

Image of FIG. 1.
FIG. 1.

Schematic of geometry and relevant dimensions for superhydrophobic surface features. (a) Ridges and (b) posts. Note that in the simulations, the air-water interface is flat.

Image of FIG. 2.
FIG. 2.

. A comparison of near wall velocity profiles obtained from Moser et al. (Ref. 30) (○) and the CFD code for turbulent channel flow between two infinite parallel plates.

Image of FIG. 3.
FIG. 3.

. A comparison of Reynolds stress profiles obtained from Moser et al. (Ref. 30) (○ , , , ● ) and the CFD code for turbulent channel flow between two infinite parallel plates.

Image of FIG. 4.
FIG. 4.

. A comparison of near wall velocity profiles obtained from Moser et al. (Ref. 30) and the CFD code (see Fig. 2 for symbol key).

Image of FIG. 5.
FIG. 5.

. A comparison of Reynolds stress profiles obtained from Moser et al. (Ref. 30). See Fig. 3 for symbol key.

Image of FIG. 6.
FIG. 6.

. Velocity profiles from simulations with (◻) and (△) ridges, as well as and (▼) posts. Regular channel profile shown for reference. Note that symbols are used to identify curves, and do not reflect data point locations.

Image of FIG. 7.
FIG. 7.

. A closer look at velocity profiles from Fig. 6, using the local friction velocity, to normalize the velocity and calculate .

Image of FIG. 8.
FIG. 8.

. Velocity profiles from simulations with (△) ridges, as well as and (▼) posts. Regular channel profile shown for reference. Note that symbols are used to identify curves, and do not reflect data point locations.

Image of FIG. 9.
FIG. 9.

. A closer look at velocity profiles from Fig. 8, using the local friction velocity to normalize the velocity and calculate .

Image of FIG. 10.
FIG. 10.

Comparison of velocity profiles for , ridges across the three Reynolds numbers investigated: (–) with , (– –) with , and with .

Image of FIG. 11.
FIG. 11.

A closer look at velocity profiles from Fig. 10, using the local friction velocity to normalize the velocity and calculate .

Image of FIG. 12.
FIG. 12.

Comparison of velocity profiles for , , posts across the three Reynolds numbers investigated: (–) with , ; (– –) with , ; and with , .

Image of FIG. 13.
FIG. 13.

A closer look at velocity profiles from Fig. 12, using the local friction velocity to normalize the velocity and calculate .

Image of FIG. 14.
FIG. 14.

Comparison of velocity profiles for transverse , ridges at (–) with regular channel profile shown for reference.

Image of FIG. 15.
FIG. 15.

A closer look at velocity profiles from Fig. 14, using the local friction velocity to normalize the velocity and calculate .

Image of FIG. 16.
FIG. 16.

Slip velocity as a percentage of bulk velocity for , ridges (△) and , , and posts (▼) at , 395, and 590, as well as transverse , ridges (◼). Note that the ridge spacing in wall units increases with increased .

Image of FIG. 17.
FIG. 17.

Slip velocity normalized by bottom-wall friction velocity for the same geometries shown in Fig. 16.

Image of FIG. 18.
FIG. 18.

Superhydrophobic surface shear stress reduction as a function of friction Reynolds number for the same geometries and Reynolds numbers reported in Fig. 16.

Image of FIG. 19.
FIG. 19.

Near-wall velocity profiles for ridges at (—) and ridges at (– –). The profiles lie atop one another, indicating the increase in Reynolds number may not affect the superhydrophobic surface performance.

Image of FIG. 20.
FIG. 20.

Superhydrophobic surface shear stress reduction as a function of for fixed ridges (△), posts (▼), and transverse ridges (◼). Transverse ridges exhibit near-zero shear stress reduction.

Image of FIG. 21.
FIG. 21.

. profiles from simulations with (◻) and (△) ridges, as well as , (▼) posts. Regular channel profile shown for reference. Note that symbols are used to identify curves, and do not reflect data point locations.

Image of FIG. 22.
FIG. 22.

. profiles for the same geometries reported in Fig. 21.

Image of FIG. 23.
FIG. 23.

. profiles for the same geometries reported in Fig. 21.

Image of FIG. 24.
FIG. 24.

. profiles for the same geometries reported in Fig. 21.

Image of FIG. 25.
FIG. 25.

. profiles from simulations with (△) ridges, as well as and (▼) posts. Regular channel profile shown for reference.

Image of FIG. 26.
FIG. 26.

. profiles for the same geometries reported in Fig. 25.

Image of FIG. 27.
FIG. 27.

. profiles for the same geometries reported in Fig. 25.

Image of FIG. 28.
FIG. 28.

. profiles for the same geometries reported in Fig. 25.

Image of FIG. 29.
FIG. 29.

. profiles from simulations with transverse , ridges (◼). Regular channel profile shown for reference.

Image of FIG. 30.
FIG. 30.

. profiles for the same geometries reported in Fig. 29.

Image of FIG. 31.
FIG. 31.

Comparison of profiles for , ridges across the three Reynolds numbers investigated: (–) with , (– –) with , and with .

Image of FIG. 32.
FIG. 32.

Comparison of profiles for the same cases discussed in Fig. 31.

Image of FIG. 33.
FIG. 33.

Comparison of profiles for the same cases discussed in Fig. 31.

Image of FIG. 34.
FIG. 34.

Comparison of profiles for the same cases discussed in Fig. 34.

Image of FIG. 35.
FIG. 35.

Schematic representing pairs of counter-rotating vortices for channel flow over ridges at two different Reynolds numbers. (a) , ridges at and (b) , ridges at .

Image of FIG. 36.
FIG. 36.

. Instantaneous streamwise velocity contour slices , normalized by , for a regular channel (a) and one with , posts (b). The slice in (a) is taken at , while the slice in (b) is taken at . Feature sizes and shapes are roughly equivalent.

Image of FIG. 37.
FIG. 37.

. Instantaneous vertical velocity contour slices , normalized by , similar to those found in Fig. 36, for the same geometries, taken at the same locations.

Image of FIG. 38.
FIG. 38.

. Time-averaged streamwise velocity contour slice (, looking downstream), normalized by , for streamwise ridges. Note that the presence of the ridges alters the mean flow up until .

Image of FIG. 39.
FIG. 39.

. A comparison of velocity correlation profiles in the streamwise direction at obtained from a regular channel (○ , , and ) and and posts at . Note that these are the same locations shown in Figs. 36 and 37.

Image of FIG. 40.
FIG. 40.

. A comparison of velocity correlation profiles in the spanwise direction at the same locations, as shown in Figs. 36 and 37. See Fig. 39 for symbol key.

Tables

Generic image for table
Table I.

Reynolds numbers, line types, geometric ratios, and length scales for the cases investigated. Note that most cases are presented in Martell et al. (Ref. 27).

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/content/aip/journal/pof2/22/6/10.1063/1.3432514
2010-06-11
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: An analysis of superhydrophobic turbulent drag reduction mechanisms using direct numerical simulation
http://aip.metastore.ingenta.com/content/aip/journal/pof2/22/6/10.1063/1.3432514
10.1063/1.3432514
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