Aircraft design is time-consuming and expensive. One of the major costs is wind tunnel testing. This involves holding a model aircraft stationary and directing air over it, to simulate and assess aerodynamic performance. Yet, since the models are stationary, such testing rarely includes the effects of engine or propeller airflow. Furthermore, test models are generally immovable, so simulations omit the action of control surfaces. Test engineers need models where such surfaces can be remotely moved during testing like a real aircraft.
The EU-funded POLITE project developed the capacity to produce such a model. Building on the work of two previous EU-funded projects, ESICAPIA and LOSITA, POLITE developed a modular model having many communal parts to be used in different tunnels. The main goals were to improve the cost-efficiency of wind tunnel model development by maximising the use of such components, and to improve testing productivity by developing new technologies for more automated testing. POLITE designed and tested a new remotely-controlled motorised flap. POLITE was part of the EU’s Clean Sky 2 programme. “A wind tunnel test, to be fully representative, must be performed in flow conditions as close as possible to what a flying aircraft would face,” explains Nicola Paletta, research & technology manager and project coordinator at IBK. “To make this possible with a scale model, you need to test it in cryogenic or pressurised environments.” Such special facilities are very expensive, so this testing is limited to a few flow conditions and model configurations. Furthermore, although models are sometimes tested in different wind tunnels, this is seldom possible for models with powered engines.
Several kinds of testing
Truly comprehensive testing requires checking under more flow conditions. Normally, that would require multiple models. “Our main improvement,” adds Paletta, “is the possibility to use the same wind tunnel model for two very different campaigns, one at low Reynolds number and another at high.” The Reynolds number (Re) is a parameter used in fluid dynamics to measure the importance of inertial effects over viscous effects. The POLITE model allows one model to be used for low-Re tests in one large non-pressurised wind tunnel and for high-Re tests in a different, pressurised wind tunnel. The modularity of the POLITE model means that more than 70 % of parts can be used for both types of testing, saving costs. This paves the way for a new design methodology that will be cheaper and more efficient than current methods. Furthermore, POLITE delivered innovative technologies aimed at improving the productivity of wind tunnel testing i.e. remotely controlled high-lift devices, up to different technological readiness levels. The team produced various prototypes of remotely controlled flaps in different configurations (single- and double-slot) tested in the laboratory with an ‘increasing complexity’ approach, including the final demonstrator of the single-slot flap installed in the actual wind tunnel model. POLITE consortium members are already exploiting the skills and techniques acquired and improved during the project for the development of new wind tunnel models. Individual partners are benefiting commercially from the increased visibility and improved capability that the project helped develop and share. The project’s work will ultimately support the development of methods to increase aerodynamic performance and efficiency. The outcome will be more efficient and less polluting aircraft.
POLITE, model, wind tunnel, aircraft, wind tunnel testing, modularity, Reynolds number, airflow