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Wind Tunnel Airflow
Researchers have explored hypersonic speed travel that entails attaining speeds over Mach 5, which is five times the speed of light for the purpose of space exploration and aircraft technologies. In order to test components and their capability to withstand airflows at such velocities, the University of Manchester in the United Kingdom combines their hypersonic wind tunnel with a thermal imaging camera from FLIR Systems.
As exploration in space rapidly progresses, it will lead to an increase in demand for re-entry space vessels that are capable of bringing payloads to orbit and re-entering the atmosphere to land safely on the Earth’s surface. The need for faster planes, both for transportation and for military purposes, will also lead to a demand for aircraft designs that are capable of withstanding high speed airflows. The wind tunnel at the University of Manchester is one of the few experimental facilities in Europe that can reach Mach numbers higher than 5.
Travelling at Mach 6, which is almost a speed of over 4000 km/h, massive airflows will rush past the vessel’s surface, causing friction, which in turn causes a rise in temperature, explains Prof. Konstantinos Kontis, head of the Aerospace Research Group at the University of Manchester. According to Kontis the hypersonic flow wind tunnel at the Manchester University is the perfect place for such tests. In this tunnel, he explains, it is possible to subject models and components to airflows similar to what they will be subjected to in the field. This rush of air will cause hot spots on the surface of the test object, which can be mapped with a thermal imaging camera. This information helps make recommendations to the company’s clients for design improvements.
Artist concept of an X-43A hypersonic flight, source: NASA.
The thermal imaging camera used in this setup is the FLIR SC655 thermal imaging camera. Kontis states that they chose this camera model because it is capable of recording thermal maps of the entire surface of the test object. It has an excellent thermal sensitivity, hence enables recording of even minute temperature differences. With the external riggering options and high speed video capturing capabilities it is the perfect tool for this type of test.
The FLIR SC655 thermal imaging camera combines high image quality and thermal sensitivity with external triggering options and high speed thermal video capturing capabilities, making it the perfect tool for hypersonic wind tunnel tests.
The air flows from the pressure chamber (to the right) through the test chamber (middle) and into the vacuum tanks (left), reaching air speeds of over 4000 km/h
From the perspective of the thermal imaging camera the air flows from left to right. The red area indicates the shock impingement area, where air friction causes an increase in heat.
The FLIR SC655 thermal imaging camera includes an uncooled microbolometer detector that produces thermal images at a resolution of 640 × 480 pixels and a thermal sensitivity of 50 mK (0.05 °C). One can capture the complete resolution at a frame rate of 50 fps and also offers high-speed windowing modes enabling the operator to improve the frame rate to 200 fps with a resolution of 640×120 pixels. The SC655 is fully compliant with both GenICam and GigE Vision protocols and is relatively easy to integrate with a variety of third-party analysis software packages.
FLIR Research software was used to capture the thermal footage and perform the initial analysis of the temperature data Kontis and research associate Dr. ErincErdem. According to Erdem, this software package is very easy to use and provides a lot of options for the researcher. It is used for capturing the data, defining special regions of interest and exporting the temperature measurement strings to third party software for an in-depth analysis of the data. The versatile software and the possibility to use embedded macros make it very easy to export data to other software programs.
Wind Tunnel Airflow
The wind tunnel includes three global components. There is a pressure chamber on one end of the wind tunnel capable of pressurizing air up to a pressure of 15 bar, 15 times the regular atmospheric air pressure. At the other end is a vacuum tank which is brought to 1 mbar, one thousandth of regular atmospheric air pressure. The test chamber is present between the two where the test object is placed. At the push of a button the pressurized air travels from the pressure chamber into the vacuum chamber, passing the test object en route with a speed of about 4000 km/h, similar to travelling at Mach 6. The FLIR SC655 thermal imaging camera is located on top of the test chamber, looking in through a Germanium window. This allows the camera to accurately map the thermal hot spots caused by the air friction, without being subjected to the force of high velocity airflows.
The FLIR SC655 thermal imaging camera is positioned above the test chamber, looking in through a Germanium window. This allows the camera to accurately map the thermal hot spots caused by the air friction, without being subjected to the force of high velocity airflows.
Prof. Konstantinos Kontis, head of the Aerospace Research Group at the University of Manchester.
Kontis’ research associate Dr. Erinc Erdem uses FLIR ResearchIR software to analyze the thermal data.
Erdem explains that in the thermal sequence, the red portion is the place where air friction causes the highest temperature rise also known as shock impingement. Beyond that, streaks are seen in the thermal image indicating the transition from laminar to turbulent airflow. He added that especially in the area of the shock impingement it is wise to strengthen the component with an extra band of insulation material of with an extra plastic coating. By taking these measures the regions of high heat flux will be better able to withstand the heat which will help prolong the lifetime of the component. The knowledge gained by these wind tunnel tests will help enhance designs for high speed aircrafts and re-entry space vessels that need to be capable of bringing payloads to orbit and returning to the Earth’s surface more or less intact. Kontis concludes that the thermal imaging camera is a crucial tool for these developments, which will lead to better version of crafts like the Boeing X-5 and the NASA X-43.
FLIR was founded in 1978, originally providing infrared imaging systems that were installed on vehicles for use in conducting energy audits. Later, we expanded our focus to other applications and markets for our technology, in particular, designing and selling stabilized thermal imaging systems for aircraft used by law enforcement. We have since grown substantially due to increasing demand for infrared products across a growing number of markets combined with the execution of a series of acquisitions. Today we are one of the world leaders in the design, manufacture and marketing of thermal imaging and stabilized camera systems for a wide variety of applications in the commercial, industrial and government markets, internationally as well as domestically.
Our Thermography business primarily consists of the design and manufacture of hand-held thermal imaging systems that can detect and measure minute temperature differences, which are useful for a wide variety of industrial and commercial applications. Uses for our Thermography products include high-end predictive and preventative maintenance, research and development, test and measurement, leak detection and scientific analysis. A growing distribution network has enabled us to penetrate existing and emerging markets and applications worldwide.
This information has been sourced, reviewed and adapted from materials provided by FLIR.
For more information on this source, please visit FLIR.