Austrian handcyclists Thomas Frühwirth and Walter Ablinger won silver medals at the 2016 Paralympics in Rio de Janeiro. Earlier, they were guests of the Institute of Fluid Mechanics and Heat Transfer at TU Graz for aerodynamic tests of their bikes and themselves. “Athletes come to us the whole year round – especially those involved in alpine winter sports, like the Austrian bobsleigh and toboggan teams. Even ski-jumpers have been tested intensively,” explains Walter Meile, who is responsible for aerodynamic research at the Institute.
A low-speed wind tunnel powered by three fans for wind speeds of up to 145 km/h is available for aerodynamic experiments at TU Graz. The special design ensures a steady and spatially very uniform stream in the test section.
Walter Meile measures how drag and lift change when the athletes take up their usual body postures and vary them slightly. Also, how the aerodynamic properties change when the materials of the sports equipment are modified. The researchers at TU Graz’s Institute of Fluid Mechanics and Heat Transfer headed by Günter Brenn can give the athletes clear feedback after wind tunnel tests so that they can immediately habituate themselves to the optimised position and posture.
Test section of the low-speed wind tunnel at the Institute of Fluid Mechanics and Heat Transfer, TU Graz.
Schematic representation of the Göttingen-type, low-speed wind tunnel with closed circuit: The air is guided from the fans via corners with turning vanes to the nozzle and into the test section, from where it enters the collector and is returned to the fans.
The low-speed wind tunnel is not just reserved for sports aerodynamics tests. Measurements in the wind tunnel are also important for vehicle engineering. “Aerodynamics influence many aspects of a vehicle – from design, efficiency and driving dynamics to driving stability during side winds and overtaking manoeuvres,” explains Walter Meile. To understand the underlying flow phenomena of real vehicles, the Aerodynamics Working Group at TU Graz’s Institute of Fluid Mechanics and Heat Transfer also works with generic models, such as the Ahmed body.
The Ahmed body is a simplified model of a vehicle well-suited for investigating an important aerodynamic property of a vehicle: the influence of the slanted rear on vehicle drag.
A recent paper of the Institute on this subject has been published in the International Journal of Heat and Fluid Flow. Further results were presented at the 26th AIAA Applied Aerodynamics Conference sowie der Conference on Modelling Fluid Flow (CMFF‘12). Results of sports science experiments on ski jumping were published in Experiments in Fluids.
The second wind tunnel at TU Graz’s Institute of Fluid Mechanics and Heat Transfer – the so-called boundary-layer wind tunnel – was especially developed for building aerodynamics to optimally reproduce the wind profile in the atmospheric boundary layer. Here, Walter Meile and his group investigate models of buildings, such as high-rise blocks. “Our aim is to assess whether the building is fit for high wind speeds in its original size”, elucidates Walter Meile. In order to simulate the wind flow properly, the whole surrounding area has to be modelled. Using a turntable, the model can be exposed to wind from various directions.
The boundary-layer wind tunnel with closed test section was specially developed for experiments on buildings where the reproduction of the atmospheric boundary layer is necessary. Using a turntable, the model can be rotated and exposed to wind from various directions.
The boundary-layer tunnel is of the Göttingen-type, similar to the low-speed wind tunnel. The important difference is that the test section is closed and the upstream run-up area reproduces the atmospheric wind profile corresponding to the natural landscape categories by means of various specific facilities.
The run-up area in the boundary-layer wind tunnel: At the nozzle outlet, the wind profile is roughly initiated by means of a grid of cylindrical rods and a saw-tooth edge. The floor of the test section can be fitted out with roughness elements of different sizes and arrangements. In this way, exponential wind-speed profiles can be reproduced over most of the test section height.
Also, research is carried out on natural ventilation concepts for residential buildings by means of experiments in the boundary-layer wind tunnel. The Institute of Fluid Mechanics and Heat Transfer is currently cooperating with the Institute of Architectural Technology at TU Graz in a research project in which a facade-opening system is being developed. The system is intended to filter contaminated air and, at the same time, fulfil requirements for well-functioning, natural ventilation in residential buildings. The experimental investigations in the wind tunnel are supported by numerical flow simulations.
Results of a research project on the subject of natural ventilation of residential buildings were published in the journal Energy and Buildings