Wild Winds: Turbulent Flow Around Structures

Introduction

Have you ever seen a wind turbine? Wind turbines are large towers with blades on top that are spun by the wind. They are a great source of clean, renewable energy. Environmental engineers have to figure out where to put wind turbines so they get the best exposure to steady, consistent winds. In this project, you will play the role of an environmental engineer and figure out whether it is a good idea to put wind turbines near tall buildings.

Background

Have you ever watched water flow through a stream or river? If there are no obstructions in the way, the water probably flows in a smooth, straight line. This is called laminar flow. However, if there is something in the water, like a rock or a branch, this causes the water to swirl and tumble as it flows by. This is called turbulent flow. The individual "swirls" are called vortices (the plural of vortex).

The same thing happens in air, when wind blows around a tall structure like a building or a tree. This is an important factor to consider when placing wind turbines, because they will generate the most power from steady winds that blow in the same direction. Inconsistent, turbulent flow can decrease power output or even damage the turbines. In this project, you will use cardboard boxes to represent "buildings" and see how they affect the flow of "wind" blowing from a fan.

Of course, turbulent flow in air is much harder for us to see! Sometimes scientists do controlled experiments using colored smoke to observe airflow. In this project you will use a streamer tied to the end of a stick to visualize the airflow.

Materials

Procedure

Observations and Results

When you held the streamer "upwind" of the box, you should have seen it blow consistently in one direction, away from the fan. This is because the flow upwind of the structure is laminar (or straight). However, when you held the streamer just "downwind" of the box, it might have fluttered around in all directions or even blown backwards. This is because the structure interrupts the smooth, laminar flow and causes turbulence. As you gradually moved the streamer away on the downwind side, its motion should have again become consistent, blowing away from the fan. This is because the flow gradually "recovers" and becomes laminar again after the turbulence is introduced.

This is important when placing wind turbines because they should not be too close to large buildings on the "downwind" side. The buildings will create turbulent flow, which will decrease the performance of the wind turbines.

More to Explore

• Science Activities for All Ages!, from Science Buddies
• Wild Winds: Detecting Turbulence Around Structures, a science project idea from Science Buddies

If you like this activity, you might enjoy exploring these related careers:

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