Aerodynamic and three-degree-of-freedom flight mechanics analysis of a slender body of rectangular cross section

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Havacılık ve Uzay Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2014

Öğrenci: BAHRİ TUĞCAN SELİMHOCAOĞLU

Eş Danışman: YUSUF ÖZYÖRÜK, HÜSEYİN NAFİZ ALEMDAROĞLU

Özet:

A slender body with rectangular cross section is considered as an aircraft countermeasure for self-protection purposes as a decoy. An initial design is necessary, for the detailed aerodynamic design of the decoy. For quick initial design purposes, three-degree-of-freedom (longitudinal, vertical, pitching) dynamic analyses of the decoy are carried out. The aerodynamic coefficients for the decoy are obtained first at different Mach numbers, angles of attack, and tail sizes with two different methodologies which are DatCOM and steady CFD analyses utilizing RANS. The comparison of these two methodologies showed that CFD results are more reliable than the DatCOM results. The aerodynamic coefficients are then input to a code numerically implementing the 3DOF motion of the decoy at different Mach numbers, center of gravity values and tail sizes. The aerodynamic coefficients necessary for this method are obtained assuming quasi-steady conditions exist, that is the angle of attack corresponding to the time of 3DOF simulation is frozen and aerodynamic coefficients are computed accordingly. For the assessment of the initial design methodology, grid independence, selection of time step for both the numerical implementation and the transient CFD analyses are considered. Also, the comparison of transient 3DOF CFD and 6DOF CFD analyses are carried out as an evaluation of 3DOF approach. The matrix of results obtained from the 3DOF numerical implementation are compared with the transient 6DOF CFD analyses. According to the results, provided the decoy has static stability, the 3DOF initial design methodology is able to capture the trend of the parameter variations, the trajectory of the decoy and the pitching angle oscillations in a conservative manner. Hence, this approach is deemed sufficient for initial design purposes of the decoy.