Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A new vortex identification method for 3-D complex flow

04.05.2016

"Vortex" is a common phenomenon in nature from tornado to turbulence, for example turbulence is a vortex buildup process (Figure 1). Investigators have realized that turbulence is not a purely stochastic process, but a process with coherent vortical structures which play a decisive role in fluid dynamics and energy transport. Therefore, accurate visualization of vortices from huge amount of data obtained by experiments and numerical simulations becomes a key issue to solve the turbulence which is a century-long scientific problem. A new vortex identification method called method, which has been published in Science China: Physics, Mechanics & Astronomy, would be greatly helpful to advance turbulence related researches.

The paper titled as "new omega vortex identification method" has been published on volume (59)2016 by Science China: Physics, Mechanics & Astronomy. The authors reviewed Helmoholtz velocity decomposition and presented a new vortex identification method: the method based on a deep understanding on physics of vortex structure.


Vortices (a) tornado (b) late boundary layer transition.

Credit: ©Science China Press

This method was given by Chaoqun Liu, a professor from the University of Texas at Arlington (UTA.) Researchers including Yong Yang from UTA, Yiqian Wang from Nanjing University of Aeronautics and Astronautics in China, Zhiwei Duan from Tsinghua University in China and Zhengzhong Sun from London City University in UK have applied this new method to variety of complex 3-D flows and all outcomes are promising, further proving the method is correct and accurate.

The authors proposed a further decomposition of the vorticity to vortical part and non-vortical part after reviewed Helmoholtzz velocity decomposition and some counterexamples like Blasius solution which has large vorticity but has no vortex. They introduced a so-called to define and identify vortex. is a ratio of vorticity square over the sum of vorticity square and deformation square.

... more about:
»3-D »astronomy »vortices

According to the ratio, vortex is defined when vorticity overtakes deformation or >0.5. The iso-surface of =0.52 is utilized to represent the vortex surface and further to visualize the vortex structure of the flow field. These researchers applied the method for 3 different cases including late boundary layer transition, supersonic micro vortex generator and roughness induced transition.

Although the three cases have very different Mach number which means the compressibility affection are quite different, the iso-surface of =0.52 well represent the vortex structure without wild adjustment of threshold for all three cases.

This is a unprecedented effort to give vortex a mathematical definition. All traditional vortex identification methods have a common critical weakness which is requirement of selection of a proper threshold. The threshold could be wildly changed case by case, time by time, and even area by area in same case.

Different thresholds will lead to different vortex structure and no one is able to know which threshold is appropriate and which vortex structure is correct. Being different from the traditional vortex identification methods, the method is quite universal and has no need to set up a threshold case by case.

In addition, the method has other advantages which include being easy to perform, having clear physical meaning, and high capability to capture both strong and weak vortices. In general, people think vortex is "vorticity tube", but the method indicates that vortex is a region where vorticity overtakes deformation and vortex is not vorticity tube.

Traditional vortex identification can cause many misunderstandings. For example, people believe turbulence is caused by "vortex breakdown", but it is now understood that this is caused by wrong selection of vortex threshold. It is convinced Dr. Liu's vortex identification method would greatly stimulate research of physics for turbulence generation and complex 3-D flows, especially for vortices dominant flows. It is also believed that many scientists and engineers would apply this method for vortex identification and vortex structure visualization.

###

For details, please see the article:

LIU Chaoqun, WANG Yiqian, YANG Yong & DUAN Zhiwei, New omega vortex identification method, Science China: Physics, Mechanics & Astronomy, 2016, to appear http://engine.scichina.com/publisher/scp/journal/SCPMA/doi/10.1007/s11433-016-0022-6

Science China Press http://www.scichina.com/

Liu Chaoqun | EurekAlert!

Further reports about: 3-D astronomy vortices

More articles from Materials Sciences:

nachricht Melting solid below the freezing point
23.01.2017 | Carnegie Institution for Science

nachricht An innovative high-performance material: biofibers made from green lacewing silk
20.01.2017 | Fraunhofer-Institut für Angewandte Polymerforschung IAP

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Quantum optical sensor for the first time tested in space – with a laser system from Berlin

For the first time ever, a cloud of ultra-cold atoms has been successfully created in space on board of a sounding rocket. The MAIUS mission demonstrates that quantum optical sensors can be operated even in harsh environments like space – a prerequi-site for finding answers to the most challenging questions of fundamental physics and an important innovation driver for everyday applications.

According to Albert Einstein's Equivalence Principle, all bodies are accelerated at the same rate by the Earth's gravity, regardless of their properties. This...

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Tracking movement of immune cells identifies key first steps in inflammatory arthritis

23.01.2017 | Health and Medicine

Electrocatalysis can advance green transition

23.01.2017 | Physics and Astronomy

New technology for mass-production of complex molded composite components

23.01.2017 | Process Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>