A wind tunnel is a device which lets researchers observe the flow over objects, forces that act on them, as well as how they interact with the flow, which now plays a more important role because of noise pollution. From the very beginning, experts have been using wind tunnels to validate aerodynamic theories as well as assist in the design of aircraft. For a considerable time, this has continued to be their main application.
At present, the aerodynamic research has extended other areas including architecture, automatic industry, education and environment, among others, which make low speed wind tunnel tests more valuable. Even if the use of CFD methods has improved over the years, numerous hours of such tests are still necessary to develop a new aircraft, wind turbine or other design that entails complicated interactions with the flow.
Because of the increase in interest of more branches of science and industry in low speed aerodynamics and the constant incapacity to come up with accurate solutions using number codes, low speed wind tunnels are necessary and impossible to replace during research and design.
One important feature of wind tunnels is the quality of flow inside the test chamber and performances in general. These structures are defined by three main criteria: maximum obtainable speed, turbulence level and flow consistency. As a result, the goal of a wind tunnel in terms of design is to have a controlled flow inside the test chamber in order to achieve the required flow efficiency and quality parameters.
When it comes to aeronautical low speed wind tunnels, those parameter requirements are exceptionally strict, which considerably increases the cost of facilities. However, low turbulence as well as high uniformity in the flow are just needed if laminar boundary layers need to be examined.
One more example of where they are used is in testing aircraft engines combustion, which requires a high-priced system that would purify air inside the tunnel to keep up the same quality of air. Another critical component of aircraft design is the noise footprint and oftentimes, this phenomenon can only be tested in a wind tunnel.
Regarding applications in the automotive industry, the car’s aerodynamic drag is obviously extremely important. However, due to the present high control level of this parameter as well as imposed speed limits, most efforts are aimed at reducing the aerodynamic noise.
Ground effect simulation is very important as well, which leads to highly sophisticated facilities so testing of noise production and ground effect simulation is allowed in the test section.
When it comes to architecture, because buildings are positioned on the ground plus they often have a considerably low height, these structures are found within the atmospheric boundary layer. So, it can be challenging to simulate the equivalent boundary layer with respect to average speed as well as turbulence level.
For majority of applications that are mostly medium and large wind tunnels, the closed test chamber and closed circuit are the typical configuration. Because of the conservation of the airflow’s kinetic energy, these structures obtain the maximum economic operation efficiency though they could be more difficult to design because of their general complexity. Therefore, these will be given more attention in this chapter.