Aerodynamic Design And Analysis For A Strut Braced Transport Aircraft Utilizing Slotted Natural Laminar Flow Airfoils

Author : Auriane Bottai
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (142 download)

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Download or read book Development of an Unsteady Aero-elastic Framework for the Study of a Slotted, Natural Laminar Flow Airfoil written by Auriane Bottai and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this research is to develop a framework for the study of the aero-elastic behavior of a truss-braced, Slotted, Natural-Laminar Flow (SNLF) wing. This type of airfoil emerged in the 2010s as a solution to significantly increase the lift coefficient while reducing the overall drag. It is composed of two encapsulated airfoils, separated by a small gap, or slot. Unlike an airfoil equipped with a flap, the aft element of such airfoil remains fixed. The aft element alleviates the pressure recovery requirement at the trailing edge of the fore element, thereby significantly extending the laminar flow region on the fore element. On the other hand, truss braced wings typically have longer span than conventional wings, which drives down the induced drag of the overall aircraft. This is permitted by the truss which adds structural reinforcement and alleviates the larger root bending moment arising from the longer span configuration. Earlier studies have found that combining those technologies for a new wing design has the potential of drastically reducing commercial aircraft fuel consumption. The present work is composed of fours parts: the first part consists of developing of an aero-elastic framework capable of predicting the aero-elastic stability of the wing. This tool is developed in time domain and proceeds by calculating the eigenvalues of the aero-elastic system. The signs of the real part of those eigenvalues determines whether the structure is stable or not. This tool is tested and validated on a classic wing configuration, the Goland wing. The second part is dedicated to the modal analysis and static stability of the \acl{snlf} wing. For this purpose, a \acl{fem} of the wing is developed. Connectors between the two airfoils are added in the geometry to maintain the profile integrity under external loading. Modal analysis with a various number of connectors showed that 13 or more connectors lead to similar mode shapes but the more connectors, the higher the natural frequencies. Fewer connectors result in significant wing deformation and deformation of the airfoil profile. \par The initial aero-elastic tool developed in this work models the two-element wing as two rectangular wings with no inter-element aerodynamic coupling. This weakness is overcome by an extensive steady flow analysis of the baseline Slotted, Natural-Laminar Flow airfoil as well as six deformed configurations in which the aft element is slightly moved upstream, downstream, upwards, downwards and rotated. This steady analysis showed that the contraction or dilatation of the gap can significantly affect the airfoil performance.Those effects are aggravated with increased Mach numbers and/or higher angle-of-attack. Conversely, if the aft element is rotated in a way that preserves the gap width, the aerodynamic coefficients remain nearly unchanged. The results of this sensitivity study are next integrated in the initially aero-elastic framework to study the aerodynamic stability of the \acl{snlf} wing, with various number of connectors. It is found that at least 13 connectors are needed to remain in the linear regime of variations of the aerodynamic coefficients. This is also the minimum number of connectors for the wing to remain stable. Finally, the behavior of the Slotted, Natural-Laminar Flow airfoil under unsteady circumstances is analyzed via a singularity based, Lagrangian method. Linear-varying strength vortex elements are distributed on the airfoil and complemented with other types of discrete singularities. The later enables corrections to the pressure coefficient and thereby the lift and moment coefficients and match the steady state loads predicted by a higher resolution flow solver. Unsteady aerodynamic coefficients up to a reduced frequency of unity of the Slotted, Natural-Laminar Flow wing with respect to vertical, chord-wise and rotational displacements of the fore and aft elements are generated with the linear-varying strength vortex method. The unsteady procedure with corrective singularities is tested on a symmetric thin airfoil and provides encouraging results. The corrective singularities are found to successfully correct the mean values of the lift coefficient but also affect the amplitude of lift and moment oscillations.