Structural conception of an engine nacelle with hybrid laminar flow control (Masterarbeit)

Kurzfassung

For application of Hybrid Laminar Flow Control (HLFC) on an engine nacelle of modern business and Commercial aircraft a structural concept was developed in this thesis. It was a major goal to get a practicable solution with a simple design and an application oriented concept. The aerodynamic calculations and the HLFC optimized geometric shape were taken from Vermeersch and Bouteiller [1]. A simplified axis-symmetrical nacelle CAD model was build from this geometric data, with the suction area on the outer surface lasting from 100mm to 350mm of cord length. To protect the boundary layer from transition caused by structural defaults and 3D obstacles, comprehensive aerodynamic surface requirements were listed. These surface criteria were oriented on the investigations of Nenni and Gluyas [2] and of Carmichael [3]. It turned out that surface contamination protection and especially insect pollution protection could be a key issue when applying the HLFC technology. With the use of a TKS fluid porous leading edge, the requirements for ice and contamination protections means can be combined in one system. This promising approach was investigated by conducting basic flight tests with a general aviation aircraft. Very good protections abilities, but only limited cleaning properties of the TKS fluid were investigated during the flight tests. The necessary amount of TKS fluid for contamination protection is approximately one Liter per engine nacelle on each flight. A design concept was developed, therefor geometrical dimensions, material suggestions and manufacturing issues were discussed and described. Carbon fiber reinforced Plastics (CFRP) and sandwich structures were implemented as far as useful. The DLR developed Tailored Skin Single Duct (TSSD) concept is used for sucking air through a micro perforated surface into one single low-pressure duct. A simple sealing concept for the suction chamber was developed regarding the issues of manufacturing and periodical maintenance. In order to fulfill the aerodynamic surface requirements, welded stud screws on the inner side were used for joining the elements. A numerical deflection and stress analysis showed that the TSSD panel deflects more than the defined surface criteria allow. Therefor a concept for stiffening the TSSD panel was developed and analyzed. Level and distribution of stress and strain are in very satisfying magnitude, so that fatigue is not endangering the HLFC nacelle. Maintenance considerations showed that a special tool needs to be used for the assembly process, because the TSSD panel must be installed from inside the nacelle. But fortunately the expected maintenance tasks are not complex and the time between periodic maintenance is comparatively long. The HLFC nacelle does not need to be disassembled for working on the engine.