Current Issue : January - March Volume : 2019 Issue Number : 1 Articles : 5 Articles
We propose an approach for the design of the subsonic part of plane and axisymmetric\nLaval nozzles for real gases. The proposed approach is based on the hodograph method and allows\none to solve the inverse design problem directly. Real gas effects are taken into consideration using\nthe chemical equilibrium model. We present nozzle contours computed with the proposed method\nfor a stoichiometric methane-air mixture. Results confirm that real gas effects have a strong influence\non the nozzle shape. The described method can be used in the design of nozzles for rocket engines\nand for high-enthalpy wind tunnels....
In this study, a time-dependent surrogate approach is presented to generate the training data for identifying the reduced-order\nmodel of an unsteady aerodynamic system with the variation of mean angle of attack and Mach number in a transonic flight\nregime. For such a purpose, a finite set of flight samples are selected to cover the flight range of concern at first. Subsequently,\nthe unsteady aerodynamic outputs of the system under given inputs of filtered white Gaussian noise at these flight samples are\nsimulated via CFD technique which solves Euler equations. The unsteady aerodynamic outputs, which are viewed as a timedependent\nfunction of flight parameters, can be approximated via the Kriging technique at each time step. By this way, the\ntraining data for any combination of flight parameters in the range of concern can be obtained without performing any further\nCFD simulations. To illustrate the accuracy and validity of the training data generated via the proposed approach, the\nconstructed data are used to identify the reduced-order aerodynamic models of a NACA 64A010 airfoil via a robust subspace\nidentification algorithm. The unsteady aerodynamics and aeroelastic responses under various flight conditions in a transonic\nflight regime are computed. The results agree well with those obtained by using the training data of CFD technique....
Free vibration (or eigenvalue analysis) is a prerequisite for aeroelastic analysis.\nFor divergence analysis, slope influence coefficients (rotation at point i due to unit load at point j) are\ncalculated using free vibration mode shapes and corresponding frequencies. The lowest eigenvalue is\nof interest and gives the divergence speed. The present paper considers the maximization problem of\neigenfrequencies for composite panels. The influence of boundary conditions and constant or variable\nstiffnesses on optimization results are investigated herein. A new convenient set of design variables\nis employed in the analysis. The computations are carried out with the use of the Rayleighâ??Ritz\nmethod and Finite Element analysis (2D quadrilateral and 3D solid elements)....
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Controlling and directing the boundary layer on the surfaces of a flight vehicle are two of the most demanding challenges in\nadvanced aerodynamic designs. The design of highly integrated and submerged inlets with a large offset between the entrance\nand compressor face is particularly challenging because of the need for controlling or reducing the adverse effects of the\nboundary layer on propulsive efficiency. S-duct diffusers are used widely in flight vehicles when the compressor face needs to be\nhidden, and their performance is generally sensitive to the quality of ingested boundary layer from the fuselage. Passive or active\nflow control mechanisms are needed to prevent flow separations at the bends. In this paper, a new method is presented for\noptimal inlet/body integration based on a pair of ridges ahead of the inlet and its effects on the performance of a semicircular Sduct\ninlet integrated on a flat surface using CFD. In this design, the ridge changes an inefficient inlet concept to one with\nacceptable performance. The new method of integration is practicable for top-mounted inlet configurations where the use of\ndiverters and other mechanisms results in higher amounts of drag, weight, and complexity....
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