Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Figuring Out Flow Dynamics

01.08.2013
Engineers gain insight into turbulence formation and evolution in fluids

Turbulence is all around us—in the patterns that natural gas makes as it swirls through a transcontinental pipeline or in the drag that occurs as a plane soars through the sky.


Turbulence structure gets more complicated as an increasing number of modes are added together.
Credit: Caltech / McKeon Lab

Reducing such turbulence on say, an airplane wing, would cut down on the amount of power the plane has to put out just to get through the air, thereby saving fuel. But in order to reduce turbulence—a very complicated phenomenon—you need to understand it, a task that has proven to be quite a challenge.

Since 2006, Beverley McKeon, professor of aeronautics and associate director of the Graduate Aerospace Laboratories at the California Institute of Technology (Caltech) and collaborator Ati Sharma, a senior lecturer in aerodynamics and flight mechanics at the University of Southampton in the U.K., have been working together to build models of turbulent flow. Recently, they developed a new and improved way of looking at the composition of turbulence near walls, the type of flow that dominates our everyday life.

Their research could lead to significant fuel savings, as a large amount of energy is consumed by ships and planes, for example, to counteract turbulence-induced drag. Finding a way to reduce that turbulence by 30 percent would save the global economy billions of dollars in fuel costs and associated emissions annually, says McKeon, a coauthor of a study describing the new method published online in the Journal of Fluid Mechanics on July 8.

"This kind of turbulence is responsible for a large amount of the fuel that is burned to move humans, freight, and fluids such as water, oil, and natural gas, around the world," she says. "[Caltech physicist Richard] Feynman described turbulence as 'one of the last unsolved problems of classical physics,' so it is also a major academic challenge."

Wall turbulence develops when fluids—liquid or gas—flow past solid surfaces at anything but the slowest flow rates. Progress in understanding and controlling wall turbulence has been somewhat incremental because of the massive range of scales of motion involved—from the width of a human hair to the height of a multi-floor building in relative terms—says McKeon, who has been studying turbulence for 16 years. Her latest work, however, now provides a way of analyzing a large-scale flow by breaking it down into discrete, more easily analyzed bits.

McKeon and Sharma devised a new method of looking at wall turbulence by reformulating the equations that govern the motion of fluids—called the Navier-Stokes equations—into an infinite set of smaller, simpler subequations, or "blocks," with the characteristic that they can be simply added together to introduce more complexity and eventually get back to the full equations. But the benefit comes in what can be learned without needing the complexity of the full equations. Calling the results from analysis of each one of those blocks a "response mode," the researchers have shown that commonly observed features of wall turbulence can be explained by superposing, or adding together, a very small number of these response modes, even as few as three.

In 2010, McKeon and Sharma showed that analysis of these blocks can be used to reproduce some of the characteristics of the velocity field, like the tendency of wall turbulence to favor eddies of certain sizes and distributions. Now, the researchers also are using the method to capture coherent vortical structure, caused by the interaction of distinct, horseshoe-shaped spinning motions that occur in turbulent flow. Increasing the number of blocks included in an analysis increases the complexity with which the vortices are woven together, McKeon says. With very few blocks, things look a lot like the results of an extremely expensive, real-flow simulation or a full laboratory experiment, she says, but the mathematics are simple enough to be performed, mode-by-mode, on a laptop computer.

"We now have a low-cost way of looking at the 'skeleton' of wall turbulence," says McKeon, explaining that similar previous experiments required the use of a supercomputer. "It was surprising to find that turbulence condenses to these essential building blocks so easily. It's almost like discovering a lens that you can use to focus in on particular patterns in turbulence."

Using this lens helps to reduce the complexity of what the engineers are trying to understand, giving them a template that can be used to try to visually—and mathematically—identify order from flows that may appear to be chaotic, she says. Scientists had proposed the existence of some of the patterns based on observations of real flows; using the new technique, these patterns now can be derived mathematically from the governing equations, allowing researchers to verify previous models of how turbulence works and improve upon those ideas.

Understanding how the formulation can capture the skeleton of turbulence, McKeon says, will allow the researchers to modify turbulence in order to control flow and, for example, reduce drag or noise.

"Imagine being able to shape not just an aircraft wing but the characteristics of the turbulence in the flow over it to optimize aircraft performance," she says. "It opens the doors for entirely new capabilities in vehicle performance that may reduce the consumption of even renewable or non-fossil fuels."

Funding for the research outlined in the Journal of Fluid Mechanics paper, titled "On coherent structure in wall turbulence," was provided by the Air Force Office of Scientific Research. The paper is the subject of a "Focus on Fluids" feature article that will appear in an upcoming print issue of the same journal and was written by Joseph Klewicki of the University of New Hampshire.

Written by Katie Neith

Contact:
Brian Bell
(626) 395-5832
mr@caltech.edu

Brian Bell | EurekAlert!
Further information:
http://www.caltech.edu

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Data use draining your battery? Tiny device to speed up memory while also saving power

The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.

Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...

Im Focus: An energy-efficient way to stay warm: Sew high-tech heating patches to your clothes

Personal patches could reduce energy waste in buildings, Rutgers-led study says

What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...

Im Focus: Lethal combination: Drug cocktail turns off the juice to cancer cells

A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.

The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...

Im Focus: New Foldable Drone Flies through Narrow Holes in Rescue Missions

A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.

Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...

Im Focus: Topological material switched off and on for the first time

Key advance for future topological transistors

Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

ICTM Conference 2019: Digitization emerges as an engineering trend for turbomachinery construction

12.12.2018 | Event News

New Plastics Economy Investor Forum - Meeting Point for Innovations

10.12.2018 | Event News

EGU 2019 meeting: Media registration now open

06.12.2018 | Event News

 
Latest News

Data use draining your battery? Tiny device to speed up memory while also saving power

14.12.2018 | Power and Electrical Engineering

Tangled magnetic fields power cosmic particle accelerators

14.12.2018 | Physics and Astronomy

In search of missing worlds, Hubble finds a fast evaporating exoplanet

14.12.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>