Use of the bench-top wind tunnel in the design of aircraft and spacecraft

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Everyone is familiar with wind tunnels and many will have seen films or pictures illustrating their use in airplanes, spacecraft design, and automotive advertisements showing how aerodynamic their cars are. Recently, new uses have been found in the design of bridges to prevent resonance under high winds and in the design of modern super-buildings to see how they interact during natural disasters caused by wind, such as hurricanes and storms. typhoons. However, there is another world of wind tunnels that many are unfamiliar with, with practical uses in everyday engineering, universities, research and development, and product design – the field of benchtop wind tunnels.

Benchtop blowers adhere to the general principles of blower design of controlled airflow, low turbulence, flow accuracy, and repeatability, but use these fundamental properties for more down-to-earth applications. The most basic of these instruments are used in the calibration of air flow measuring devices called anemometers and the more complex are used in small-scale aerodynamic studies. New applications have emerged recently for tabletop wind tunnels in everyday engineering. These new applications include the analysis of the thermal characteristics of heat-emitting elements, such as printed circuit boards and electronic components, as well as the measurement of heat sinks, heat exchangers and other heat transfer devices. cooling.

Wind tunnel elements

Benchtop blowers are open-loop systems that pull air into and out of the room rather than recirculating it through a duct or other closed-path system. Regardless of their size, all wind tunnels have some key things in common. The test section, or inner tube, is usually the smallest component of the device, but it is the most important for the user. These sections usually have a rounded or square cross section where the test conditions exist, and measurements are taken. The other components of the blower are involved in controlling the airflow required for the test chamber and may include the fan / blower section to mobilize air, a series of honeycombs, vanes, filters and other devices to reduce air turbulence and produce laminar air flow, as well as an area of ​​duct cross sections that shape the air flow through the test chamber.

Figure 1. Laboratory grade blower shown with control panel (Omega Engineering, Inc.)

Applications

The simplest application is the calibration of the air flow of the anemometer. Anemometers are devices that measure air speed and are used in many scientific and technical disciplines. There are two common types, both of which use different technologies. These are the finned air speed anemometer and hot wire anemometer, which use small fans in response to the air flow and resistive elements to cool the air, respectively. Throughout the industry, anemometers are used for a multitude of tests and airflow adjustments in general ventilation systems in workspaces, monitoring the speed of airflow in cabins sprayers, hoods, clean rooms and laminar flow workstations. They are also used to measure flow through large filters and cooling or heating coils used in industrial processes. Anemometers are widely used in the scientific community and find use in meteorological measurement and analysis, in environmental studies, and for research. The most common use of these devices is during installation and maintenance of HVAC systems, where they are used for balancing and measuring airflow, and troubleshooting.

In the calibration of anemometers, a wind tunnel is very easy to use and does not require any special knowledge. The test chamber is often configured to accept specific models and the airflow is pre-calibrated against a NIST standard. To operate, all you have to do is mount the unit to be tested, choose the air flow rate and read the flow rate. The unit in figure 2 is controlled by the dashboard shown – A multi-position switch selects the air flow.

Benchtop calibration blower (Omega Engineering, Inc.)

Figure 2. Benchtop calibration blower (Omega Engineering, Inc.)

For more general applications, a model like the one shown in Figure 1 offers greater flexibility. This device can be used in laboratory calibrations, as well as in applications suitable for larger units, including aerodynamic studies using models. Common uses include product design and development, R&D projects, and academic experiments. The test chamber can accommodate custom mounting devices and instruments. It also includes the ability to measure temperature, humidity and barometric pressure. Laboratory grade blowers have much wider flow ranges than calibration blowers – 25 to 9,000 fpm (feet per minute) versus 500 to 3,000 fpm. In addition, the flow rates are continuously variable and are not preset, as they are located in a calibration blower. The lowest flow rates are achieved using specially designed restrictive plates that reduce air while maintaining high uniformity and low turbulence.

The most recent application to the surface of these compact air circulation devices is in everyday engineering design, as well as in thermal evaluation of electrical and electronic components. This includes active devices such as circuit boards and powered components, and passive devices such as heat sinks and heat exchangers.

On the surface, these devices are a far cry from the familiar designs used for studies and calibration of airflow. As you can see from the example on the left, unlike its traditional counterparts, the airflow chamber is the largest part of the unit. The fans can be individually controlled and draw air through the honeycomb filter to suppress turbulence and produce an even flow. The unit under test is suspended in the air chamber on a universal and adjustable mounting bracket that can accept a wide range of test objects. There are several openings in the test chamber that allow other instruments, such as sensors and anemometers. The air flow is continuously variable so that different test conditions can be used and temperature profile measurements made. This device can also be operated using a small control box or via a PC interface.

Benchtop thermal evaluation blower (Omega Engineering, Inc.)

Figure 3. Benchtop thermal evaluation blower (Omega Engineering, Inc.)

Conclusion

Wind tunnels are not a common tool for the average engineer. However, the little-known category of benchtop wind tunnels offer great advantages in terms of test, measurement and design efficiency for the right applications. For those who regularly use anemometers, a benchtop calibration blower is an easy way to increase your in-house calibration capacity. For those working in research and product development, a laboratory unit can be a critical data resource. For those who design circuit boards, heat-generating components, heat sinks or other cooling devices, the thermal evaluation wind tunnel presents a new way to create safer, more reliable and better products. If you fall into one of these categories and you’ve never heard of benchtop blowers, welcome to a new path to productivity.

This information has been obtained, reviewed and adapted from documents provided by OMEGA Engineering Ltd.

For more information on this source, please visit OMEGA Engineering Ltd.


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