Featured Research

from universities, journals, and other organizations

Smooth sailing: Rough surfaces that can reduce drag

Date:
January 17, 2014
Source:
American Institute of Physics (AIP)
Summary:
From the sleek hulls of racing yachts to Michael Phelps’ shaved legs, most objects that move through the water quickly are smooth. But researchers have found that bumpiness can sometimes be better. They modeled the fluid flow between two surfaces covered with tiny ridges and found that even in turbulent conditions the rough surface reduced the drag created by the friction of flowing water.

From the sleek hulls of racing yachts to Michael Phelps' shaved legs, most objects that move through the water quickly are also smooth. But researchers from UCLA have found that bumpiness can sometimes be better.

"A properly designed rough surface, contrary to our intuition, can reduce skin-friction drag," said John Kim, a professor in the mechanical and aerospace engineering department at UCLA. Kim and his colleagues modeled the fluid flow between two surfaces covered with tiny ridges. They found that even in turbulent conditions the rough surface reduced the drag created by the friction of flowing water. The researchers report their findings in the journal Physics of Fluids.

The idea of using a rough surface for reduced drag had been explored before, but resulted in limited success. More recently scientists have begun experimenting with rough surfaces that are also extremely difficult to wet, a property called superhydrophobicity. In theory this means that the surfaces can trap air bubbles, creating a hydrodynamic cushion, but in practice they often lose their air cushions in chaotic flows.

The ULCA team chose to model a superhydrophobic surface design that another group of researchers at UCLA had already observed could keep air pockets entrapped, even in turbulent conditions. The surface was covered with small ridges aligned in the direction of flow.

The researchers modeled both laminar and turbulent flows, and unexpectedly found that the drag-reduction was larger in turbulent conditions. The irregular fluctuations and swirling vortices in turbulent flows on smooth surfaces generally increase drag, Kim explained. However, the air cushion created by the superhydrophobic ridges altered the turbulent patterns near the surface, reducing their effect, he said.

The team expects insights gleaned from their numerical simulations to help further refine the design of rough, drag-reducing surfaces. Further down the line, such surfaces might cover the undersides of cargo vessels and passenger ships. "It could lead to significant energy savings and reduction of greenhouse gas emissions," Kim said.


Story Source:

The above story is based on materials provided by American Institute of Physics (AIP). Note: Materials may be edited for content and length.


Journal Reference:

  1. Hyunwook Park, Hyungmin Park, John Kim. A numerical study of the effects of superhydrophobic surface on skin-friction drag in turbulent channel flow. Physics of Fluids, 2013; 25 (11): 110815 DOI: 10.1063/1.4819144

Cite This Page:

American Institute of Physics (AIP). "Smooth sailing: Rough surfaces that can reduce drag." ScienceDaily. ScienceDaily, 17 January 2014. <www.sciencedaily.com/releases/2014/01/140117153637.htm>.
American Institute of Physics (AIP). (2014, January 17). Smooth sailing: Rough surfaces that can reduce drag. ScienceDaily. Retrieved September 3, 2014 from www.sciencedaily.com/releases/2014/01/140117153637.htm
American Institute of Physics (AIP). "Smooth sailing: Rough surfaces that can reduce drag." ScienceDaily. www.sciencedaily.com/releases/2014/01/140117153637.htm (accessed September 3, 2014).

Share This



More Matter & Energy News

Wednesday, September 3, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Halliburton Reaches $1B Gulf Spill Settlement

Halliburton Reaches $1B Gulf Spill Settlement

AP (Sep. 2, 2014) Halliburton's agreement to pay more than $1 billion to settle numerous claims involving the 2010 BP oil spill could be a way to diminish years of costly litigation. A federal judge still has to approve the settlement. (Sept. 2) Video provided by AP
Powered by NewsLook.com
Google Teases India Event, Possible Android One Reveal

Google Teases India Event, Possible Android One Reveal

Newsy (Sep. 1, 2014) Google has announced a Sept. 15 event in India during which they're expected to reveal their Android One phones. Video provided by Newsy
Powered by NewsLook.com
Australian Airlines Relax Phone Ban Too

Australian Airlines Relax Phone Ban Too

Reuters - Business Video Online (Aug. 26, 2014) Qantas and Virgin say passengers can use their smartphones and tablets throughout flights after a regulator relaxed a ban on electronic devices during take-off and landing. As Hayley Platt reports the move comes as the two domestic rivals are expected to post annual net losses later this week. Video provided by Reuters
Powered by NewsLook.com
Hurricane Marie Brings Big Waves to California Coast

Hurricane Marie Brings Big Waves to California Coast

Reuters - US Online Video (Aug. 26, 2014) Huge waves generated by Hurricane Marie hit the Southern California coast. Rough Cut (no reporter narration). Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins