Search results

The purpose of this paper is to carry out a comprehensive study of compressible flow over double wedge and biconvex airfoils using computational fluid dynamics (CFD) and three analytical models including shock and expansion wave theory, Busemann's second‐order linearized approximation and characteristic method (CHM).

Flow over double‐wedge and biconvex airfoils was investigated by the CFD technique using the Spalart‐Allmaras turbulence model for computation of the Reynolds stresses. Flow was considered compressible, two dimensional and steady. The no slip condition was applied at walls and the Sutherland law was used to calculate molecular viscosity as a function of static temperature. First‐order upwind discretization scheme was used for the convection terms. Finite‐volume method was used for the entire solution domain meshed by quadratic computational cells. Busemann's theory, shock and expansion wave technique and CHM were the analytical methods used in this work.

Static pressure, static temperature and aerodynamic coefficients of the airfoils were calculated at various angles of attack. In addition, aerodynamic coefficients of the double‐wedge airfoil were obtained at various free stream Mach numbers and thickness ratios of the airfoil. Static pressure and aerodynamic coefficients obtained from the analytical and numerical methods were in excellent agreement with average error of 1.62 percent. Variation of the static pressure normal to the walls was negligible in the numerical simulation as well as the analytical solutions. Analytical static temperature far from the walls was consistent with the numerical values with average error of 3.40 percent. However, it was not comparable to the numerical temperature at the solid walls. Therefore, analytical solutions give accurate prediction of the static pressure and the aerodynamic coefficients, however, for the static temperature; they are only reliable far from the solid surfaces. Accuracy of the analytical aerodynamic coefficients is because of accurate prediction of the static pressure which is not considerably influenced by the boundary layer. Discrepancies between analytical and numerical temperatures near the walls are because of dependency of temperature on the boundary layer and viscous heating. Low‐speed flow near walls causes transformation of the kinetic energy of the free stream into enthalpy that leads to high temperature on the solid walls; which is neglected in the analytical solutions.

This paper is useful for researchers in the area of external compressible flows. This work is original.

The purpose of this paper is to obtain close form expressions for the dynamic stability of conical wave riders with flat surfaces which could be equipped with lifting surfaces on its plain flat surface. Numerical simulation would require very large meshes to resolve flows at subscale level and the experimental evaluations would be equally difficult, requiring expensive measurement facilities with challenging procedures to secure such vehicles in confined test sections to obtain satisfactory wind on and wind off oscillations.

The design method uses appropriate pressure fields using small disturbance theory, which, in turn, is perturbed using the unsteady shock expansion theory to recover suitable expressions for the dynamic stability behaviour.

It was observed that the dynamic stability of the standard half-cone-type wave riders with flat upper surfaces deteriorates with the axis position measured from the pointed apex reaching a minimum at around x/co = 0.666. The half-cone wave rider with flat upper surfaces is dynamically less stable than a pure cone.

The method is typically less accurate when the similarity parameter M_∞θ ≤ 1 = 1 or if the angle of attack is not small.

With renewed interest in hypersonic, future hypersonically would be designed as fast lifting bodies whose shapes would be close to the configurations of hypersonic wave riders, especially if they are designed to operate at upper atmosphere altitudes.

The analytic approach outlined in this paper for the evaluation of dynamic and static stability derivatives is original, drawing from the strengths of the small disturbance theory and shock expansion techniques. The method is particularly important, as there are no reported theoretical, numerical or experimental results in the literature.

An aerothermodynamic design code for axisymmetric projectiles has been developed using a viscous‐inviscid interaction scheme. Separate solution procedures for the inviscid and the viscous (boundary layer) fluid dynamic equations are coupled by an iterative solution procedure. Non‐equilibrium, equilibrium and perfect gas boundary layer equations are included. The non‐equilibrium gas boundary layer equations assume a binary mixture (two species; atoms and molecules) of chemically reacting perfect gases. Conservation equations for each species include finite reaction rates applicable to high temperature air. The equilibrium gas boundary layer equations assume infinite rate reactions, while the perfect gas equations assume no chemical reactions. Projectile near‐wall and surface flow profiles (velocity, pressure, density, temperature and heat transfer) representing converged solutions to both the inviscid and viscous equations can be obtained in less than two minutes on minicomputers. A technique for computing local reverse flow regions is included. Computations for yawed projectiles are accomplished using a coordinate system transformation technique that is valid for small angle‐of‐attack. Computed surface pressure, heat transfer rates and aerodynamic forces and moments for 1.25 &le Mach No. &le 10.5 are compared to wind tunnel and free flight measurements on flat plate, blunt‐cone, and projectile geometries such as a cone‐cylinder‐flare.

The term ‘hypersonic flow’ was first used by Tsien in 1946 to denote a (low for which the main stream Mach number was large compared with unity, and he demonstrated that such flows displayed characteristic features which justified the use of a special name. Tsien confined his considerations to a perfect gas with constant specific heats but since 1946 interest has widened to the flow of real fluids at high Mach numbers, this interest being mainly stimulated by the problems of the re‐entry at high speeds into the earth's atmosphere of missiles and satellites. An essential feature of hypersonic flow is that relative to the undisturbed flow direction the inclination of the nose shock of a body immersed in the fluid is of the same order of magnitude as the mean inclination of the surface over the forward part of the body, and the region between shock and body, the so‐called ‘shock layer’, is relatively narrow there. Another characteristic feature is the high temperature that developes in this layer in problems of practical interest and the associated effects on the physical and chemical properties of the medium. Thus, not only must account be taken of the variation of the specific heats with temperature for a real fluid but the consequences of dissociation and ionization of the fluid on crossing the nose shock must be considered. The interaction of the boundary layer with the flow external to it and with the nose shock becomes of increasing importance, as well as increasingly complex, with increase of main stream Mach number. Finally, account must be taken of the molecular nature of the medium in problems where the density is sufficiently low for the mean free path of the molecules to be a significant ratio of a typical dimension of the body or of its boundary layer thickness.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued.

There can be few scientific and engineering subjects which have progressed as rapidly as the theory and practice of high‐speed aerodynamics and jet propulsion during recent years. The number and scope of papers that have poured out from research establishments, universities and the industry are such that it has been impossible for all but the very gifted to keep ahead of developments in more than a few limited aspects of the subjects.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued

To suppress fatigue damage and ensure structural safety, this paper aims to analyze the effect of the damage accumulation on the aeroelastic model of an air-breathing hypersonic flight vehicle (AHFV).

Initially, by constructing the modified longitudinal elastic model of an AHFV, the stress condition of the fuselage is analyzed, and the model differences with the rigid body are studied. Then, a new damage dynamic model is presented to describe the damage dynamic evolution. Finally, combining the damage model and the longitudinal model of the AHFV, the key variables affecting the damage accumulation are determined.

It is demonstrated that the elastic deformation must be considered when analyzing the damage characteristics of the fuselage and to determine the key variables that affect the damage accumulation, which provides a more accurate reference for improving the structural reliability and lifespan of AHFVs.

The novelty of this paper comes from the application of the force and stress models for the damage evolution of the AHFV and the development of a new damage model for the entire body with the elastic dynamics of AHFVs.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued

FOLLOWING the talk given by Mr William C. Hitt of the Douglas Aircraft Company last June, which was reported in Aircraft Engineering for July, the S.L.A.E. organized a meeting at which the subject could be further discussed. Mr R. A. Fry was in the chair, and the first paper, by Mr William C. Hitt, was delivered by his son, Mr Lloyd Hitt.