Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session Q06: Boundary Layers: Superhydrophobic Surfaces (3:55pm  4:40pm CST)Interactive On Demand

Hide Abstracts 

Q06.00001: Fluid retention in liquid infused surfaces: A direct numerical simulation study Martand Mayukh Garimella, Stefano Leonardi Liquid infused surfaces (LIS) are surface textures wetted with infused liquid lubricant and can reduce turbulent drag up to 35%. However, for practical use, these surfaces must be designed to withstand the shear of the external flow. In previous studies, ideal texture geometries such as infinite longitudinal bars have been used. However, these geometries fall short in retaining the lubricant and sustaining drag reduction. Therefore, in this study, we have tried to model texture geometries which can retain the lubricant. For this purpose, we performed direct numerical simulations of a turbulent channel flow with a texture made of rectangular cavities. A viscosity ratio between the lubricant and the main stream of fluid, m=0.4 is defined. The aspect ratios of the cavities, and the Weber number are varied. Compared to the flow over longitudinal bars, the rectangular mesh has additional transverse bars to close the cavity. This increases the drag but helps in retaining the lubricant. For the finite surface tension cases, a rebounding capillary pressure wave propagation is observed for the mesh configuration altering the flow dynamics close to the wall. Overall, this texture sustains the drag reduction and decreases the turbulent intensities showing promise for further studies. [Preview Abstract] 

Q06.00002: Effect of interface deformation and contact line motion on turbulent skinfriction drag reduction with superhydrophobic surfaces Amirreza Rastegari, Rayhaneh Akhavan Effect of interface deformation and contact line motion on turbulent skinfriction Drag Reduction (DR) with SuperHydrophobic (SH) surfaces is investigated by DNS using a twophase freeenergy lattice Boltzmann method. DNS studies were performed in turbulent channel flows at $Re_{\tau_0} \approx 222$ with SH longitudinal microgrooves of width $15 \le g^{+0} \le 64$ at solid fractions of $\phi_s=$1/16 \& 1/2 on both walls. Simulations were performed at viscosity ratios of $\mu_{ext}/\mu_{int}=50$, Weber numbers of $We_{\tau_0} \equiv \rho u_{\tau_0} \nu/\sigma \approx 2 \times 10^{3}$ and dynamic contact angles of $\theta_{adv} = 112^{\circ}$ and $\theta_{rec} = 106^{\circ}$. Two initial configurations of SH interfaces were investigated, corresponding to contact angles of $\theta_c = 90^{\circ}$ and $120^{\circ}$. Contact line motion was found to magnify the apparent wetted surface area of the microgrooves, thus reducing the effective streamwise slip velocities by 750\%. Interface deformation was found to enhance the effective spanwise slip velocities by up to 200\% with initially curved interfaces. These combined effects lead to drops of 732\% and 1650\% in the magnitude of DR with initially flat and curved interfaces, respectively, compared to `idealized' flat SH walls. [Preview Abstract] 

Q06.00003: Analysis of wallnormal jets induced by bubble oscillations on superhydrophobic surfaces Kimberly Liu, Ali Mani Superhydrophobic surfaces (SHS) have received significant attention for achieving drag reduction by reducing skin friction drag. Experimental results of patterned SHS have shown that pressure control can sustain wallattached air films and that the dynamic modulation of air film height can lead to even further drag reduction. It has been observed that, under such conditions, rapid change in the height and shape of the air film can induce substantial wallnormal velocities (Wang and Gharib, J. Fluid Mech. 2020). In this work, we numerically characterize these jetlike flows structures in a laminar setting. We present an assessment of the effects of the free shear boundary condition, which corresponds to the dynamic slip condition of the experimental air films, and the effects of an otherwise noslip boundary condition, which corresponds to unsteady wall deformation. Interaction of the induced nearwall flow structures with turbulent crossflow and implications on possible drag reduction of the turbulent boundary layer will be discussed. [Preview Abstract] 

Q06.00004: Stability Limits of LiquidInfused Surfaces and Their Effects on Turbulent Drag Johan Sundin, Stephane Zaleski, Shervin Bagheri Liquidinfused surfaces (LIS) have shown great potential in decreasing drag for turbulent flows. They consist of surface structures infused with another liquid, and are relatively robust against failure due to turbulent pressure fluctuations, in contrast to superhydrophobic surfaces. However, their stability depends on the surface tension and the surface chemistry of the surface. We investigate the stability limits for the case of square longitudinal grooves with infused liquid, using direct numerical simulations at friction Reynolds numbers around $Re_\tau = 180$. The interface is described using a volumeoffluid (VOF) framework, allowing large interface deformations as well as moving contact lines. The viscosity ratio is kept at the order of 1, representing realistic values of oilwater systems. A large contact angle causes the contact line to depin and move into the groove. For our geometry, however, mass conservation is a stabilizing effect, because if the interface depins on one position, it is raised elsewhere. Due to the finite surface tension, the surface creates an apparent slip, but damps only parts of the wallnormal velocity fluctuations. A too low surface tension causes large capillary waves to form, increasing drag dramatically. [Preview Abstract] 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2023 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700