A note on the Kutta condition in Glauert's solution of the thin aerofoil problem

Glauert's classical solution of the thin aerofoil problem (a coordinate transformation, and splitting the solution into a sum of a singular part and an assumed regular part written as a Fourier sine series) is usually presented in textbooks on aerodynamics without a great deal of attention being paid to the rôle of the Kutta condition. Sometimes the solution is merely stated, apparently satisfying the Kutta condition automatically. Quite often, however, it is misleadingly suggested that it is by the choice of a sine series that the Kutta condition is satisfied. It is shown here that if Glauert's approach is interpreted in the context of generalised functions, (1) the whole solution, i.e. both the singular part and any non-Kutta condition solution, can be written as a sine-series, and (2) it is really the coordinate transformation which compels the Kutta condition to be satisfied, as it enhances the edge singularities from integrable to non-integrable, and so sifts out solutions not normally representable by a Fourier series. Furthermore, the present method provides a very direct way to construct other, more singular solutions. A practical consequence is that (at least, in principle) in numerical solutions based on Glauert's method, more is needed for the Kutta condition than a sine series expansion

Structures and Materials in the 90s - Concept and Prospects.

Worldwide, the impact of technical and economic developments has always been strongly affected by the exploitation of new materials. It appears that advanced materials and structural design technology presently form the basis of an new thrust of technical innovation in which decreasing specific weight is the common denominator in all components. Structures and materials in aeronautical constructions in the 50s and 60s were isotropic, homogeneous and metallic. In the 70s and 80s more and more non-isotropic, inhomogeneous and non-metallic structures and materials came into use. Today, the airframe of a modern military aircraft already consists of 50 % fibre reinforced composites. This led to a drastic decrease in weight together with increased flight performance. Advanced ceramics and composites appear to play a fundamental role in the development of a new generation of hypersonic flight vehicles

Unsteady Aerodynamic Forces on an Oscillating Wing at High Incidences and Flow Separation.

Based on wind tunnel measurements on a low-aspect-ratio trapezoidal half-wing model in incompressible flow, some characteristic features of motion-induced unsteady airloads at high incidences and flow separation are presented and discussed. Special emphasis is placed on the effect of the motion of the wing on the flow separation processes and on the investigation of the interactions between the separated flow phenomena on the stationary wing and the motion-induced unsteady airloads on the oscillating wing. It is shown that these airloads are strongly affected by the flow separations and that their prediction from inviscid potential-flow theory may lead to rather unrealistic results in buffeting response calculations

Challenges and Perspectives in Computational Aeroelasticity.

The impetus of Computational Unsteady Aerodynamics (CUA) in the development of advanced aeroelastic prediction capabilities is highlighted. First, current challenging problem areas in aero- elasticity are pointed out, and recent progress in CUA is surveyed with the focus on transonic and separated flows. Future trends in CUA are then outlined and, finally, challenges and perspectives in the computational simulation of the aeroelastic and flight dynamic behaviour of complete aircraft and spacecraft are discussed

New Ultra High Capacity Aircraft (UHCA) - Challenges and Problems from an Aeroelastic Point of View.

To meet future air transport requirements, technical studies of a new class of Ultra High Capacity Aircraft (UHCA) with passenger capacities of 600 and possibly more are presently being conducted in many aircraft companies. Thereby, the aircraft designers are faced with a variety of new and challenging technical problems. Among those, aeroelastic problems are generally accepted to be of primary concern. It appears that with increasing size and hence structural flexibility of such super transport aircraft limits of technical feasibility are being approached. In the present paper the impact of aeroelasticity on the design of UHCA is highlighted. First, the adverse effects of static aeroelastic deformations on the controllability, aerodynamic performance and static flight stability of such highly flexible aircraft with swept-back wings are discussed,and the design concept of an aeroelastic adaptive wing is outlined. Then, as a dynamic aeroelastic key problem, the wing-with-engine nacelle flutter stability problem is analyzed, and corresponding flutter stability boundaries are presented. Finally, some other important dynamic aeroelastic problems relevant to UHCA are pointed out, namely the gust load design problem, the influence of structural flexibility on the dynamic flight performance and stability, and aeroservoelastic problems arising with the application of automatic flight control systems using active control technology

A Parametric Study of the Flutter Stability Characteristics of Turbomachine Cascades.

A parametric study of the unstalled flutter stability character- istics of compressor and turbine cascades in subsonic and super- sonic flow is carried out. Based on typical section two- dimensional cascade models, stability boundaries and dominant trends in flutter behaviour are outlined with emphasis on the effects of a) single mode structural coupling in bending and torsion, b) coupling among multiple blade degrees of freedom, c) mass ratio and structural damping, d) compressibility, e) cascade solidity and stagger, f) steady aerodynamic blade loading. Practical design aspects are in the foreground of all of these investigations

Parametric Studies of the Flutter Stability Characteristics of Turbomachine Bladings

Parametric studies on the unstalled flutter stability characteristics of compressor and turbine cascades are carried out based on typical section two-dimensional aeroelstic models. Flutter stability boundaries and dominant trends in flutter behaviour are presented with emphasis on the effects of (a) single mode structural coupling in bending and torsion, (b) coupling among multiple blade degrees of freedom, (c) mass ratio and structural damping, (d) compressibility, (e) cascade solidity and stagger, and (f) steady aerodynamic blade loading