Wind Tunnel Test For Breakthrough Laminar Aircraft Demonstrator Europe at DNW-LLF

The purpose of the CleanSky Smart Fixed Wing Aircraft Integrated Technology Demonstrator (SFWA ITD) is to bring innovative technologies, concepts and capabilities currently from Technology Readiness Level (TRL) 3 to 6 by demonstrating the potential to contribute to a step change in fuel consumption level. The Smart Fixed Wing Aircraft ITD is addressing the integration of passive and active flow and load control technologies into new Smart Wing concepts, to achieve a significant reduction in aircraft drag (10%) and wing drag (25%) using laminar flow concepts and applying innovative control surfaces for load control. To prove the project objectives, flight tests are planned with the BLADE (Breakthrough Laminar Aircraft Demonstrator Europe) flight test demonstrator. Prior to demonstration of these new technologies in flight, large scale experiments have been conducted at realistic close to flight conditions to support the flight clearance process by identifying critical flight conditions and validating Computational Fluid Dynamics tools. In the framework of the CleanSky project designated with the acronym BLAME (Breakthrough Laminar Aircraft Model wind tunnel testing in Europe) low-speed aerodynamic wind tunnel tests were carried out on a A340-300 aircraft model. The tests were conducted in the 8m x 6m closed test section of the Large Low-Speed Facility (DNW-LLF). The DNW-LLF is well known for its low ‘free-stream’ turbulence level and thus suited for laminar flow investigations. The main aim of this test campaign was to check the installation effect of the outboard wing natural laminar flow (NLF) panel on the A340-300 Airbus flying demonstrator aircraft MSN 001, designated the BLADE aircraft. This paper will focus on the measurement techniques used for this test campaign. To establish the effects of the NLF panel (installation) aerodynamic data was gathered using, among other techniques, a strain gauge internal balance. Measurement uncertainty will be discussed based on an earlier proposed uncertainty definition and on wind tunnel data for this model. For this (well maintained) model a large set of aerodynamic data is available spanning more than 20 years providing the opportunity to gain insight in the application potential of the proposed uncertainty definition. In this campaign two challenges emerged, from a wind tunnel simulation point of view. The first was correct simulation meaning it was vital to obtain the locations of the laminar to turbulence boundary layer transition line on the NLF panel. Despite the large scale of the model and the facility (attaining a relative high Reynolds number) the Reynolds number effects have to be taken into account. The location of the transition line was visualized by means of the Infra-Red Thermography technique. (IRT). The second was the deformation of the wing section at the location of the NLF panel. This information is essential in comparing measured experimental NLF panel flow behaviour with theoretical results. The deformation measurements were done by means of an optical measurement technique using CCD cameras to determine the local wing twist deformation. In the paper the technical solutions to master these challenges during the large scale wind tunnel test will be described.