Drag reduction by shock and boundary layer control. Results of the project EUROSHOCK II, supported by the European Union 1996--1999.
This book presents experimental and numerical results of the Euroshock II project for reducing drag on a transonic airfoil in an active way (idea of control). This follows a previous effort, the Euroshock I project, where drag reduction was attempted in a passive way. This former endeavour led to negative results. Passivity meant that a cavity was placed on the upper part of the airfoil. A reduction in wave drag was observed, but it was largely absorbed by increased viscous drag for laminar flows, and the turbulent case was not encouraging either. Such negative results led to the Euroschock II project. The next step was to consider active suction devices on the wing. Four cases were examined: discrete suction on the top of the wing, suction before a bump, suction within a cavity, suction after a cavity. The research was streamlined along four directions: a modelling phase, a computational approach, wind tunnel experiments, control applications. The results are: 1) active single cavity control with part suction leads to wave drag reduction without increase of viscous drag, but the suction rates are too high to be implemented realistically. 2) Suction behind a passive cavity leads to a similar situation but now shock spreading is independent of the suction rates. 3) Discrete suction reduces the boundary layer thickness downstream to any level desired. Wave drag increases with the suction rate, especially if the suction device is placed near the front of the wing. If it is placed near the rear end of the wing, viscous drag increases. So, an optimal solution corresponds to a middle way placement of the suction device. 4) A bump placed near the shock region will reduce wave drag and hopefully will not increase viscous drag. A general conclusion is that adaptive bumps seem the most promising control devices for drag reduction in the context of this study. A second part in the book presents fourteen contributions supporting the above-mentioned results and grouped after the four directions of research mentioned above.
scientific article; zbMATH DE number 2127491