Swirling flow patterns in a computer simulation of turbulence Click on image for full size (102K JPEG) Courtesy of G. Brethouwer (Royal Inst. Tech., Sweden)

Turbulence is disordered motion of a fluid. What does disordered mean? Well, as some scientists are fond of saying, "it's hard to define but you'll know it when you see it" (the same can be said for alot of other things too, including life itself).

You can get a good idea of what turbulence is by thinking about what all turbulent flows have in common:

• Vorticity
  A spinning column of fluid is called a vortex (plural vortices) and since turbulence is loaded with vortices we say it possesses vorticity. This is especially true if the object itself is spinning like a planet or star in which case vorticity is generated by the Coriolis effect. Examples of vortices include hurricanes on Earth, dust devils on Mars, and the spiral galaxies are vorticies.
• A wide range of scales
  Scales here means different sizes and time intervals. For example, Jupiter's atmosphere has vortices more than 100,000 km (60,000 miles) wide which encircle the entire planet, vortices less that 1 km (0.6 miles) wide which are no bigger than a tornado, and everything in between, including the Great Red Spot, which is about 15,000 km (10,000 miles) across.
• Unpredictability (chaos)
  Turbulence is unpredicable in the sense that two turbulent flows which look almost exactly the same at one instant may look completely different a short time later. This is sometimes called the butterfly effect and it's the reason why we have to use statistics to describe turbulence. For example, scientists can predict the probable path of a hurricane but they can never be 100% certain.
• Efficient mixing and dissipation
  Turbulent fluids are good at stirring; if you put milk in your tea turbulence will mix it up far more rapidly than if you put milk in a cup of molasses. Turbulence also is good at dissipating energy - this is why cars and airplanes are designed to be as streamlined as possible. Streamlined shapes reduce turbulence and therefore reduce drag.

In astronomical objects such as planets and stars turbulence is usually caused by buoyancy (warm fluid rises and cool fluid sinks due to gravity) or shear (winds or currents going in different directions).

Swirling flow patterns in a computer simulation of turbulence Click on image for full size (102K JPEG) Courtesy of G. Brethouwer (Royal Inst. Tech., Sweden)

Nothing to worry about - turbulence is natural and it happens all over the universe, from river rapids to Jovian planets to stars to nebulae! You can even see turbulence when you pour milk into a cup of hot tea.

Turbulence is just a fluid moving around crazily so it's all mixed up. Turbulent flows are filled with swirling and spiraling motions. This is especially true if the object itself is spinning like a planet or star where the Coriolis effect causes winds and currents to curve and wiggle around. It's difficult to predict what a turbulent flow is going to do because of something called the butterfly effect.

Swirling flow patterns in a computer simulation of turbulence Click on image for full size (102K JPEG) Courtesy of G. Brethouwer (Royal Inst. Tech., Sweden)

Nothing to worry about - turbulence is natural and it happens all over the universe, from river rapids to Jovian planets to stars to nebulae! You can even see turbulence when you pour milk into a cup of hot tea.

Turbulence is just a fluid moving around crazily so it's all mixed up. It's difficult to predict what a turbulent flow is going to do because of something called the butterfly effect.