Wind Tunnel Testing
The need for an artificial wind was early stated in Smeaton (1759), in a trial to test windmill sails. Wind tunnels appeared during the late 1800s to plan and execute the testing required to aid in man's quest to fly. One of the early documented wind tunnels is the one built by the Wright brothers at the end of 1901 for flight tests of their 1900 and 1901 gliders. The wind tunnel was a simple open-loop design with a fan pushing a flow of air through an enclosed square box (NASA, 2013).
Schematic of an open-loop wind tunnel: a fan is usually located at the exit of the test section, not to generate undesired turbulence in the flow
Schematic of a closed-loop wind tunnel: closed-loop wind tunnels usually have at least two sections
The concept of wind tunnel testing is to blow air on a test model at various wind direction angles. The test model is usually placed on a turntable to allow for wind direction change. When the objective is to reproduce the lower part of the atmospheric boundary layer (up to several hundred meters from the earth's surface), the wind tunnel is called a Boundary Layer Wind Tunnel (BLWT). BLWTs are classified as open-loop or closed-loop systems. An open-loop wind tunnel has the inflow and the outflow disconnected, which is not economical from an energy perspective. Contrarily, closed-loop wind tunnels save energy by recirculating the airflow. Special vanes turn the airflow around the corners while minimizing turbulence and power losses to reduce running costs. Straight-line winds are modeled in BLWTs. Atmospheric boundary layer (ABL) profiles are reproduced by passive/active management techniques.
Significant savings in the construction cost of infrastructure can be achieved by doing a wind tunnel study in the preliminary design stages, especially when the infrastructure is located in a hurricane-active area or will be subject to moderate to high winds during its expected lifespan. The location of a construction project in an unusual terrain or surrounding structures makes wind tunnel testing crucial to optimize cost efficiencies, generate accurate results to enhance safety, and allow for maximum design freedom. Wind tunnels are vital for wind impact studies: structures (buildings, bridges, towers, energy infrastructure, solar panels, wind turbines, power transmission lines, and towers, etc.), wind comfort near buildings, effects of wind on the ventilation system in a building, wind climate for wind energy, air pollution dispersion, internal pressure studies, crosswind effects on vehicles, wind effects on sailing yachts, cables aerodynamics, etc.
- Aly, A.M. (2014), "Atmospheric boundary-layer simulation for the built environment: past, present and future," Building and Environment, 75, 206-221.
- NASA, (2013), https://www.grc.nasa.gov, webage visited in October.
- Smeaton, J. (1759). On the Construction and Effects of Windmill Sails. The Philosophical Transactions of the Royal Society, 51.