Aerodynamics for engineering students - part 9

thiết bị. Theo đó, trong những gì sau tối đa hóa nâng aerofoils một yếu tố được xem xét tại mục , tiếp theo là mục aerofoils nhiều yếu tố và các loại khác nhau của nắp, và mục về các phương pháp kiểm soát boundarylayer khác. Cuối cùng, các phương pháp khác nhau được sử dụng để giảm kéo được mô tả trong mục 8,5 8,8. | 486 Aerodynamics for Engineering Students devices. Accordingly in what follows the maximization of lift for single-element aerofoils is considered in Section followed by Section on multi-element aerofoils and various types of flap and Section on other methods of boundarylayer control. Finally the various methods used for drag reduction are described in Sections to . Maximizing lift for single-element aerofoils This section addresses the question of how to choose the pressure distribution particularly that on the upper wing surface to maximize the lift. Even when a completely satisfactory answer is found to this rather difficult question it still remains to determine the appropriate shape the aerofoil should assume in order to produce the specified pressure distribution. This second step in the process is the so called inverse problem of aerofoil design. It is very much more demanding than the direct problem discussed in Chapter 4 of determining the pressure distribution for a given shape of aerofoil. Nevertheless satisfactory inverse design methods are available. They will not however be discussed any further here. Only the more fundamental question of choosing the pressure distribution will be considered. In broad terms the maximum lift achievable is limited by two factors namely i Boundary-layer separation and ii The onset of supersonic flow. In both cases it is usually the upper wing surface that is the more critical. Boundarylayer separation is the more fundamental of the two factors since supercritical wings are routinely used even for subsonic aircraft despite the substantial drag penalty in the form of wave drag that will result if there are regions of supersonic flow over the wing. However no conventional wing can operate at peak efficiency with significant boundary-layer separation. In two-dimensional flow boundary-layer separation is governed by a The severity and quality of the adverse pressure gradient and b The kinetic-energy .

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