نوع مقاله : مقاله پژوهشی
نویسندگان
1 دانشگاه صنعتی مالک اشتر تهران
2 گروه هوافضا، دانشکده فنی مهندسی، دانشگاه آزاد اسلامی، واحد علوم و تحقیقات تهران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
The dynamic response of a natural laminar flow airfoil undergoing harmonic small-amplitude pitching oscillations is investigated using Large-eddy simulations with a chord-based Reynolds number of Re = 750;000. Throughout the pitch cycles, large changes in the transition point are seen as well as trailing-edge separation. This leads to a nonlinear response of the aerodynamic forces. Although the nature of the flow is highly nonlinear, the development of the boundary layer over the airfoil surface can be modeled using a simple phase-lag concept which suggests a quasi-steady evolution of the boundary layer. Based on this phase-lag assumption, a simple new empirical model is developed which agrees very well with the measured experimental data. With the aid of this model, the primary source of non-linearities in the unsteady aerodynamic forces is identified to be the quasi-steady term, which can be evaluated from the static airfoil characteristics. The strength of this remains unchanged with the variation of reduced frequency, but the harmonic term's strength, which models the unsteady effects, increases with increasing frequency.
کلیدواژهها [English]
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