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Kỹ thuật máy bay chiến đấu Episode 2 Part 4

Tham khảo tài liệu 'kỹ thuật máy bay chiến đấu episode 2 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 312 AIRCRAFT DESIGN within each cell using various convergence schemes to equate the flow properties along the boundaries connecting the cells. While gridding the space around a simple cylinder or a lone wing can be easily automated the gridding of the flowfield around a full aircraft must currently be done manually and can literally take months. Figure 12.40 reprinted with permission from Ref. 82 illustrates the complexity of the flowfield gridding. Note for example where the canopy meets the fuselage and where the cells must fan out in the empty region between wing and canard. Gridding is especially important because the CFD results are highly sensitive to the shaping of the cells. You can actually get different answers for the same aircraft using two different gridding schemes. According to the author of Ref. 82 this sensitivity is more pronounced than that due to the type of mathematical model being used e.g. NS vs Euler equations. To address the gridding problem researchers are investigating artificial intelligence Al approaches to gridding. Another approach is the computa-tionally-adaptive gridding in which the gridding scheme is automatically adjusted based upon the CFD results. Skyrocket Aerospace Plane Concept 13 PROPULSION 13.1 INTRODUCTION All forms of aircraft propulsion develop thrust by pushing air or hot gases backward. In a simplified case the force obtained can be determined using Newton s equation F ma by summing all the accelerations imparted to the air. This is shown for fluid flow in Eq. 13.1 where s is the cross-sectional area of the fluid acted upon by the propulsion system V is the fluid velocity and the zero subscript indicates the freestream condition. The propeller or jet engine is assumed to magically accelerate the air from velocity Fo to V. The rate of useful work done by the propulsion system called the thrust power P equals the product of the thrust force and the aircraft velocity Eq 13.2 . The kinetic energy imparted to the fluid by