Research On Aerodynamic Design And Optimization Platform For Low Speed Aircraft In Near Space

Transition occurs on aircraft surface when air flows around and laminar flow becomes turbulence, while wall friction in laminar boundary layer is far more less than that in turbulent one. Natural Laminar Flow (NLF) optimization means to lower the flight drag and promote flight performance by modifying the body shape curve and realizing preferred pressure distribution, through which transition delayed and the laminar flow area extended. Flight tests illustrate that modern technology of manufacture and production has fulfilled the requirements to realize extended laminar flow on practical aircraft surface. Low speed aircrafts in Near Space that fly above the altitude of 20 km are easier to realize NLF on surfaces, as they work in low Reynolds number regime and low turbulence level atmosphere. Meanwhile, it makes the work of optimization more practical and meaningful considering their characteristics of the simple flight condition and the pursuit of high lift to drag performance.As a probe research of NLF optimization, the thesis incorporatedγ-Re_θtransition model to predict the onset of transition, constructed an integrated software platform based on Computer Aided Design (CAD) technology, Computational Fluid Dynamics (CFD) technology and modern optimization method. In application of the platform, geometry modify, mesh generation, fluid computation and results processing could be performed automatically on PC or high performance cluster, and optimal NLF shape would present according to different requirements for different aircrafts when modern optimization work flow are finished.The results of the transition model calculation showed that,γ-Re_θtransition model reflected clearly the transition phenomenon in the flow regime we care, and its prediction ability satisfied basically the requirement of initial NLF optimization. The application of the platform to Stratospheric Airship and High Altitude UAV showed that, different objectives considerably influenced the optimization results, so it was important to bring forward reasonable objectives and constrains according to design requirements and aircraft characteristics. With proper design and optimization rules, the results with transition model incorporated were superior to those turbulence results when focused on the lift to ratio performance, and the feature of flow in Near Space flight were utilized consequently.It will require much more practical considerations to realize stable laminar flow and bring in to play the advantages in Near Space flight. However, it lacks theory and practice knowledge when more factors are taken into account, including turbulence attribute at high altitude, surface roughness and vibration effect, etc. The design rules and results in the thesis still need experimental and practical tests. Luckily, the platform constructed here is more meaningful as it is easy to assembly state of the art analysis methods, take into account deep apprehension of correlative problems and give out more reliable and practical results, to promote the design level of low speed aircraft in near space.