This project validated a cleaning device capable of clearing out small debris from the leading edges of business jets or airliners, to keep the flow as laminar as possible on the leading edge of the wing. The cleaning concept was compatible with the surface treatment of the leading edge of commercial aircrafts. Typically this concerns the contamination of leading edges by insect impact. At first, the system was designed and a prototype manufactured. In parallel, aerodynamic and stress models were studied. Then ground experiments including tests in a wind tunnel were performed, in view of prototype validation. The prototype was subsequently modified and validated. Conclusions helped the industrialisation of the cleaning system.
The consortium was led by EPFL, who co-ordinated a preliminary project on the design of such cleaning devices in the Clean Sky call 3 CLEANLE, with several partners for manufacturing, consulting, experiment running and analysis, including a design office SME, and university wind tunnel experts. The project led to a test prototype.
The project pushed the concepts, that have attained a Research Technology Readiness Level, TRL near to TRL3 (research to prove feasibility), to evolve on the system/subsystem model and prototype demonstrator of a technology demonstration of TRL 6.
The system had been designed in WP2 with extensive use of numerical engineering methods: computational fluid dynamics (CFD) software for estimating the aerodynamic forces encountered in flight, computational magnetostatic to size the magnets holding the cleaning devices on the wing and computational solid mechanics to size the components and estimate the loads on the structural parts. The design phase of WP2 had been extended to M8 in order to integrate all conclusions from WP3.
In WP3 (Pre-tests) a method for contaminating wing surfaces with flies had been devised and built. It consisted on a modified leaf-blower which « shoots » fruit flies (Drosophilae) at a speed of 130 Km/h and can thus contaminate surfaces in a representative way. Additionally, a laser based sensor had been chosen to measure contaminants height before and after the tests. Cleaning tests had been performed on aluminium sheets contaminated with the aforementioned procedure. Various cleaning tools (brushes, sponges, cloths) had been used for cleaning in both dry and wet conditions using 3 different liquids. For the best combination of sponge and liquid it was possible to clean sufficiently the wing after 4 passes. Using a more abrasive sponge leads to scratches on the aluminium sheet. However, it was assumed that a painted wing will be more resistant to scratches, allowing the use of more abrasive sponges and/or more pressure applied on the sponges). This was tested in WP6. An important result of WP3 was that dry cleaning proves ineffective, so that a cleaning liquid is necessary.
Scraping the wing leading edge with a nylon string has been tested on an aluminium cylinder and proved successful. This method was used to clean the high curvature part of the leading edge.
For the ground tests it had been decided to « shrink » the reference wing leading edge. 3 test zones had been selected (which correspond to wing root, mid wing and wing tip) which are connected with transition zones. The wing was built from scratch and mounted on a structure which allows rotation of the wing to ease the contamination process and the application of weights that simulate the aerodynamic loads. Transition zones were built with wood and covered with aluminium sheets to limit the cost. The CleanLE prototype had been updated to take into account comments of the experimental test team (ZHAW), to increase the mechanical stability of the prototype (various CSM simulation have been performed), to ease manufacturing of the parts and to limit cost by choosing as many off-the-shelf parts as possible. CleanLE prototype manufacturing was completed, manufacturing of the wing was ongoing.
The setup for the wind tunnel test bench consisted in two endplates 4.7m long, 2.6m height, placed 1.0m apart and installed in the main test section. The wing, equipped with the prototype cleaning device, was held by the rotating guiding devices integrated in the endplates in order to vary precisely the angle of attack. PPMA plane disks attached to and rotating with the guiding devices allowed the fixation of the wing. The wing geometry was constructed by taking a representative section of the reference wing (at 1/3 of the span) and extruding it for 1m with a 10° sweep. The devices were then placed on both sides of the wing in the central section. An adaptation was necessary along the span of the model to be able to test the three angles of sideslip and keep the device in the middle of the test section. Flat plates mounted on the wing near the endplates were used to « trap » the boundary layer developing on the endplates. To gather information about the flow 64 pressure sensors were used whose positioning had been decided after extensive CFD simulations. Additionally, oil flow visualisation were performed. The wing had been manufactured and the mounting of the experimental setup was ongoing.
WP 5 was delayed until M17 instead of M14 due to longer than expected test bench design phase in WP4; timeline had been compressed to fit into the time line of the project (24 months). Testing (WP's 6 and 8) and Optimisation (WP7) were being now run in parallel with cross-iterations to achieve completion of the project within 24 months.