What makes a vortex visible

Trailing vortices deflect the flow behind the wing downward. This is called downwash, and it reduces the amount of lift produced by the wing.

In order to make up for that lost lift, the wing must go to a higher angle of attack, which increases the drag generated by the wing. The pressure imbalance that produces lift creates a problem at the wing tips. The higher-pressure air below a wing spills up over the wing tip into the area of lower-pressure air above.

These wing tip vortices create a form of pressure drag called vortex drag. Vortices reduce the air pressure along the entire rear edge of the wing, which increases the pressure drag on the airplane. Despite the technicality of the name, lock vortex flow is an everyday phenomenon where its formation and the way it flows is very easy to understand. In fact, in some cases, this type of vortex is actually an advantage rather than a problem.

It's easier to explain lock vortex flow when it's used in a situational example. So, take the pickup truck's tailgate for instance.

Some people think it's more fuel efficient to drive with the tailgate down and others believe that it's ideal to drive with the tailgate up. Which one is correct then? Well, first of all, lock vortex flow provides a precise scientific answer to this.

When a pickup truck is driven with the tailgate down, a straight stream of air builds up inside the open perimeter of the pickup. This increases the wind drag on the vehicle and slows it down which means that more work or energy is required to keep the pickup at speed. However, if you drive with the tailgate up, because the open perimeter is now an enclosed space, rotating air bubbles lock vortex flow are formed from the oncoming wind flow.

The consecutive wind flow, once the lock vortex flow is formed, are deflected off the vehicle and passes through creating only minimal drag. So, driving a pickup truck with the tailgate up is the ideal scenario. This type of vortex typically causes structural problems as the intensity of the build up of the wind around structures results into failure.

When a speeding wind gets into contact with a building's exterior surface, a build up of wind pressure accumulates. Since wind force is a dynamic action, the pressure created at a building's surface also produces vibrations.

To make the vortices visible, I created a horizontal cut plane through the center of the box, on which the so-called Q-criterion , an established method for vortex identification, is visualized. In addition, the pressure distribution on the cylinder is visualized by means of color representation.

The pressure clearly oscillates with the frequency of vortex shedding, which is visible in the animation. The Q-criterion for identification of vortices is visualized on a horizontal cut plane in the 3D model of turbulent flow around a cylinder.

The flow patterns are on a much smaller scale due to the higher Reynolds number and associated increased turbulence level. I hope you enjoyed our short excursion into the world of vortex streets.

For a computationally inexpensive way to start, I recommend the Flow Past a Cylinder tutorial model from the Application Gallery. This consent may be withdrawn. Really cool.

How does one go about plotting the Q-Criterion for an unsteady turbulent flow past a rotating geometry for example a wind turbine and such. Thanks Victor.

You can apply it to any other turbulent 3D-model, e. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' or the latest version listed if standards is not an option. Log Out Log In Contact. The Beauty of Vortex Streets. Set the bottles down and watch the vortex form.

You can make the vortex more visible by adding a little food color to the water or some glitter or little foam beads. See how big you can make the vortex by spinning the water faster. Experiment with washers that have different size holes. See what happens when you tilt the bottle after a vortex has formed.

Vortex and Ice Cubes Another experiment that you can do with vortices is quite simple and yet demonstrates an important principle of meteorology. What you need: A large mug or a small pot A spoon Some ice Try This: Pour some very hot water into the cup or pot and stir it slowly in one direction so the water is rotating slowly you may want to put some food color in so you can see the water better.

Next place a small ice cube at the center of the rotating water.