Friction drag reduction of Taylor–Couette flow over air-filled microgrooves
release_y4ntqpopyfflnatf2xr7n2uzha
by
Xiaochao Liu,
Chenxi You,
Yanlin Cao,
Baorui Xu,
Yantao Yang,
Hongyuan Li,
Pengyu Lv,
Chao Sun,
Huiling Duan
Abstract
Reducing drag under high turbulence is a critical but challenging issue that has engendered great concern. This study utilizes hydrophilic tips in superhydrophobic (SHP) grooves to enhance the stability of plastron, which results in a considerable drag reduction (<jats:inline-formula>
<jats:alternatives>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022112024009480_inline1.png"/>
<jats:tex-math>$DR$</jats:tex-math>
</jats:alternatives>
</jats:inline-formula>) up to 62 %, at Reynolds number (<jats:inline-formula>
<jats:alternatives>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022112024009480_inline3.png"/>
<jats:tex-math>$Re$</jats:tex-math>
</jats:alternatives>
</jats:inline-formula>) reaching <jats:inline-formula>
<jats:alternatives>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022112024009480_inline4.png"/>
<jats:tex-math>$2.79 \times 10^{4}$</jats:tex-math>
</jats:alternatives>
</jats:inline-formula>. The effect of the spacing width <jats:inline-formula>
<jats:alternatives>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022112024009480_inline5.png"/>
<jats:tex-math>$w$</jats:tex-math>
</jats:alternatives>
</jats:inline-formula> of the microgrooves on both <jats:inline-formula>
<jats:alternatives>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022112024009480_inline6.png"/>
<jats:tex-math>$DR$</jats:tex-math>
</jats:alternatives>
</jats:inline-formula> and flow structures is investigated. Experimental results demonstrate that <jats:inline-formula>
<jats:alternatives>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022112024009480_inline7.png"/>
<jats:tex-math>$DR$</jats:tex-math>
</jats:alternatives>
</jats:inline-formula> increases as either microgroove spacing <jats:inline-formula>
<jats:alternatives>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022112024009480_inline8.png"/>
<jats:tex-math>$w$</jats:tex-math>
</jats:alternatives>
</jats:inline-formula> or <jats:inline-formula>
<jats:alternatives>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022112024009480_inline9.png"/>
<jats:tex-math>$Re$</jats:tex-math>
</jats:alternatives>
</jats:inline-formula> increases. The velocity fields obtained using particle image velocimetry indicate that the air-filled SHP grooves induce a considerable wall slip. This slip significantly weakens the intensity of Taylor rolls, reduces local momentum transport, and consequently lowers drag. This phenomenon becomes more pronounced with increasing <jats:inline-formula>
<jats:alternatives>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022112024009480_inline10.png"/>
<jats:tex-math>$w$</jats:tex-math>
</jats:alternatives>
</jats:inline-formula>. Furthermore, to quantify the multiscale relationship between global response and geometrical as well as driving parameters, <jats:inline-formula>
<jats:alternatives>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022112024009480_inline11.png"/>
<jats:tex-math>$DR\sim (w, \phi _s, Re)$</jats:tex-math>
</jats:alternatives>
</jats:inline-formula>, a theoretical model is established based on angular momentum defect theory and magnitude estimate. It is demonstrated that a decrease in the surface solid fraction can reduce wall shear, and an increase in the groove width can weaken turbulence kinetic energy production, rendering enhanced slip and drag reduction. This research has implications for designing and optimizing turbulent-drag-reducing surfaces in various engineering applications, such as transportation and marine engineering.
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