An analytical investigation was conducted to determine the aeroelastic flutter and divergence behavior of a cantilevered, composite, forward swept rectangular wing. The influence due to the variation in the bendingtorsion stiffness coupling of the tailored wing on the flutter and divergence critical dynamic pressure is analyzed. The analytical approach utilizes the incompressible two-dimensional unsteady aerodynamic strip theory. Flutter and divergence velocities were obtained by using an optimization procedure that solves exactly the coupled bending-torsion equations for a cantilevered swept wing. The results indicate that the flutter and divergent of a fixed-root wing involve a compromise, since the bending-torsion stiffness that maximizes the flutter velocity tends to minimize the divergent speed and vice versa.

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Here we review experimental and computational studies of the pulsed detonation engine concept (PDEC) and present results of our recent numerical study of this concept. The PDEC was proposed in the early 1940s for small engine applications; however, its potential was never realized due to a complicated, unsteady operation regime. In this study, we demonstrate the use of current advances in numerical simulation for the analysis of the PDEC. The high-thrust/engine volume ratio obtained in our simulations demonstrates promising potential of the pulsed detonation engine concept. IntroductionE ARLY developments of engine technology leading to practical propulsion engines were almost completely associated with steady-state engine concepts. Unsteady concepts, which initially appeared promising, never evolved from the conceptual state and have remained for the most part unexplored. The early work in unsteady propulsion suffered from a lack of appropriate analytical and design tools, a condition which seriously impeded the advancement of the unsteady concepts to a practical stage.In this paper, we review the historical development of unsteady propulsion by concentrating on the particular concept of the intermittent detonation engine, and discuss current research activities in this area. A review of the literature 1 ' 24 reveals that a significant body of experimental and theoretical research exists in the area of unsteady propulsion. However, this research has not been extended to the point where a conclusive quantitative comparison can be made between impulsive engine concepts and steady-state concepts. For example, the analysis given in Refs. 8-11 of the performance of a detonation engine concept includes neither frequency dependence nor analysis of losses due to multicycle operation. A new generation of analytical and computational tools exists today and allows us to revisit and analyze such issues with a high degree of confidence. Numerical simulation has developed to the state where it can now provide time-dependent two-and three-dimensional modeling of complex internal flow processes 20 ' 24 ' 25 and will eventually result in tools for systematically analyzing and optimizing engineering design. In addition to a review of applications of the pulsed detonation engine concept (PDEC), we will report results of a numerical study of an air-breathing detonation engine. This study was performed using new unsteady computational fluid dynamics (CFD) tools that we will also describe.Our paper is structured as follows: 1) historical review of the pulsed detonation development efforts; 2) description of the basic phenomenology of the air-breathing pulsed detonation engine concept; 3) description of the mathematical formulation and new numerical scheme used to simulate the problem; 4) discussion of the simulation results; and 5) conclusions. Constant-Volume CombustionFrom the very early development of jet-propulsion engines, it was known that an engine based on a constant-volume combustion process achieves higher thermodynamics ef...

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