Technical University of Dresden Wind Tunnel

24/05/2017 Industry innovation

A look back at the wind tunnel’s history

The wind tunnel at the TU Dresden can look back on a long and storied history. The wind tunnel was built in conjunction with the construction of the Type 152 Passenger Aircraft, Germany’s first scheduled passenger transportation aeroplane. However, due to a lack of economic efficiency the development of the aircraft was not pursued any further. After the cancellation of aviation projects in Dresden, the wind tunnel was repurposed for alternative uses. Aerodynamics for use in the building and automotive sectors became the new focus of research. With the establishment of the Aviation and Aerospace Technology Institute, the wind tunnel was put back into use for the aviation sector.

An overview of the wind tunnel

TU Dresden’s low-speed wind tunnel uses a closed circuit design. A closed wind tunnel of this nature is also referred to as a Göttingen tunnel.

An open jet test section was added in order to provide better accessibility to the models, and better visualisation of measurements. For teaching purposes in particular, the open jet test section provides better visibility for the observing engineers than closed construction allows.

The technical construction of the wind tunnel is designed to address all relevant scenarios that need to be covered with an impressive degree of effectiveness.

For example, the nozzle antechambers, diffusors, and manifolds are made from steel-reinforced concrete, with the exception of the flow straighteners.

Power in the TU Dresden wind tunnel is provided by two DC current motors, each of which provides a sustainable power output of 150 kW. A maximum output of 190 kW is also possible for short periods. The two wind tunnel turbines feature seven and five blades respectively. The transformer, which is connected to the local 20 kV power network, provides the energy for the power unit. Wind speed is regulated by adjusting the rotation speed of the fans, which can be adjusted seamlessly from virtually zero through to the maximum speed. 

The diameter of the circular nozzle outlet and measurement cross section in the low-speed wind tunnel is three metres. The three-metre diameter nozzle allows a wind speed of 40 km/h, while the maximum speed of 60 m/s involves the three-metre nozzle being replaced by a two-metre nozzle instead.

Sporting uses in the wind tunnel

A wide variety of exciting projects are performed in the wind tunnel of the TU Dresden, ranging from projects for the aviation sector through to sport and environmental aerodynamics. Sporting projects, in particular, benefit from TU Dresden’s extensive experience. National teams from all over Europe use the wind tunnel to improve their high-tech sporting equipment. As such, bobsleds are tested in the wind tunnel, while other winter sports such as skeleton or speed skating benefit from the option of using the stationary wind flow that the tunnel generates. Speed skaters can improve their posture in the TU Dresden’s wind tunnel, while clothing fabrics are tested for their aerodynamics. Racing bikes for track cycling are also tested for their “slipperiness” in the tunnel.

Up-and-coming sports such as indoor skydiving are also tested in the TU Dresden wind tunnel. Flying suits for indoor skydiving must have particular characteristics to allow free flight. These suits are also made from a particularly tough material and are tested for their suitability in the TU Dresden wind tunnel.

Aviation projects in the wind tunnel

Extreme, high-risk scenarios, such as fire outbreaks, place extremely high demands on the materials that are used in aircraft construction. These materials and components must resist an outbreak of fire, as well as dealing with loss of pressure that an on-board fire can cause. In case of pressure drop, the lining panels which are the cargo compartment cladding between the cargo hold and the passenger cabin make sure that the area in which damage occurs is released and that therefore pressure compensation is ensured fast enough. This allows the aircraft to remain controllable and equalise the on-board pressure. This functionality is tested on original structures in the high-speed wind tunnel in Merkers, in Thüringen. Only after these tests have been performed with flawless results are they used in a real-world setting. The wind tunnel in Merkers features a high-speed camera, which records at 10,000 frames per second, and which is used to record the observation zone, after which the results are evaluated. The results of the investigation are used to certify the aircraft.

The high speed wind tunnel in Merkers is located in a former potash mine and is operated by the TU Dresden. The large, airtight tunnels in the salt mine are used as pressure accumulators, which means that the energy required can be drawn from the network over a longer time and then released, at a much greater power level, during measurement. The combination of the two wind tunnels results in a comprehensive and versatile range of measurements for the University.

Efficiency is an important topic for the aviation industry, alongside improving transportation capacity and environmental friendliness. The result is increased focus on improving the efficiency of the next generation of aircraft. In the low-speed wind tunnel, TU Dresden has experimentally tested the influence of lift and drag forces exerted by pneumatic mini trailing-edge devices (TEDs). MiniTEDs are specially arranged exhaust ports that are attached to the trailing edge of the flaps. The MiniTEDs increase lift and allow a steeper climb, thereby reducing aircraft noise in the area around the airport. To that end, TU Dresden has investigated the suction of air volume flowing over the spoiler’s trailing edge. Evaluation by TU Dresden of the initial model showed that, when flow is applied, it is possible to increase lift by sucking air over the spoiler’s edge while retaining control over the amount of lift.

Use of the wind tunnel by students is similarly wide-ranging. Students who belong to the Academic Flying Group, Akaflieg, enjoy the possibility of getting to the bottom of interesting aerodynamic challenges as part of their degree coursework. For example, the preliminary theoretical considerations and experimental confirmation of the validity of an overload warning sensor were explored by TU Dresden’s students, both in the wind tunnel and in free flight.

In addition to work on degrees and diplomas, the Chair also enables students in aviation and space technology to gain practical experience of aerodynamics, as well as delivering lectures and practical exercises in aviation aerodynamics and thermal fluid dynamics.

Future prospects for the wind tunnel

Many exciting projects are currently being delivered via TU Dresden’s wind tunnel. These include examinations of air resistance, dynamic lift or object deformation are significant areas of interest in the operation of the TU Dresden wind tunnel. With the newly build DLR Software Research Institute, there are new possibilities for future collaboration on future wind tunnel projects.

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