Journal of Aerospace Mechanics
Year:2006 | Volume:1 | Issue:3|Papers Count:9

Thermodynamic calculations of the combustion heat release, specific impulse, and volumetric specific impulse show that metal fuels can exceed hydrocarbon fuels in volumetric energy content and in the case of boron exceeds conventional fuels on a mass basis as well. The refractory nature of metal fuels and their combustion products also suggest that they may permit ramjets utilizing subsonic combustion to extend their operation to hypersonic Mach numbers. In this paper, formation of stabilized flame using a pure powdered metal fuel without the use of hydrocarbons is investigated experimentally. The ability to effectively inject powdered, metal into a combustor is demonstrated using a laboratory-scale dispersion apparatus. Dynamic parameters of burning time and flame speed of aluminum dust flame have been measured by dust combustion apparatus. Results imply that the burning time is decreased, while the oxygen concentration is increased.Also, the replacement of nitrogen with argon increases burning time. This is, because of the increase in aluminum dust reaction rate. The flame speed of aluminum dust is near the diffusion flame and its differences with hydrocarbon fuel flame are to stabilize the dust flame in rich mixtures.

Film cooling has many applications such as in the gas turbine blade cooling, where inholes are introduced in the blades from which the cooling fluid are injected to the main stream covers the blade surface. In this research, turbulent three-dimensional film cooling over a flat plate is numericallying investigated. Reynolds-averaged Navier-Stokes approach is applied for the simulations, using the standard k-e and shear stress transport models. Also, the simulations are performed using large eddy simulation approach with the Smagorinsky subgrid scale model The finite volume method and the SIMPLE algorithm are applied in both simulations and the spatial and temporal terms are discretized using the power-law and the Crank-Nicolson schemes, respectively. At 90° injection angle, the results are compared with previous experimental and numerical results showing close agreements. Optimum values of velocity ratio and injection angle are obtained using the film cooling effectiveness Parameter…

In this article, the accuracy of two mixed explicit-implicit schemes for simulating non-relativistic, radiative hydrodynamic phenomenon in the equilibrium diffusion limit is compared. In mixed explicit-implicit schemes, the radiation hydrodynamics equations are solved in two stages. In the first stage (the hydrodynamics stage) a finite-volume Godunov type method is utilized. In the second stage (the radiation stage), two different methods are used. In the first method, a linearized non-iterative implicit technique is used. In the second method, a Jacobian-free Newton-Krylov procedure is used to solve the diffusion (radiation) equation. Several examples are considered to demonstrate the accuracy and convergence properties of the two schemes used. Numerical results indicate that, the second method is more accurate. However this method is much more time consuming.

The suspension system of tracked vehicles, in comparison with riding vehicle..., has special specifications (i.e. continuity of suspension system). In this paper, at first, a planar mathematical model (1/2- model) of a tracked vehicle was introduced along with the dynamical equations and state-space representation. The parameters of spring and damper coefficients are then optimized and the vehicle performance against standard inputs was studied. For preliminary analysis, only standard inputs and impulse of projectile has been discussed. The results showed the stability of the system with satisfactory margins.

In this paper, the effects of two important parameters on characteristic curves and the calibration of hot films and hot wires are studied experimentally. One of them is the free stream temperature and the other is the probe temperature or probe overheat ratio. The results show that increasing the wind tunnel (free stream) temperature decreases the voltage of the Weston's bridge in the Constant Temperature Anemometry (CTA) circuit. It must be noted that, the decreasing rate depends on the physical properties of sensors, the flow velocity, and the overheat ratio. Temperature correction factors can be used for modification of these errors. Also, consideration of probe temperature shows that the calibration curves of a probe, in different overheat ratios, can be matched using a suitable correction factor, i.e. if the calibration curves of a probe were available only for two different overheat ratios, the other calibration curves for any arbitrary one can be obtained.

Vibratory gyroscopes, having small sizes and low prices are commonly used in civil and defense industries. In these type and gyroscopes, which are translation based, the resonators mass is vibrated due to harmonic forceo. The input angular velocity causes Coriolis effect and at the same time the vibration of the resonator. The amplitude of these effects are the same to the input angular velocity. In this article, the governing dynamical equations of vibratory gyroscopes are presented. Then, the response of the system to different inputs is analyzed.

In spite of great deal of experience, cruise missile design is still a complex engineering problem and many decisions are made based upon qualitative choices by the design team. The use of genetic algorithm (GA), as a conceptual design optimization methodology for cruise missiles, can help reduce the need for qualitative decisions. In this article, the results of the design optimization code based on a 6-DOF simulation are discussed, witch shows the ability of GA to perform cruise missile conceptual design. The results of this work have been compared with the world best missile (Harpoon). Using this method, the designer can follow a systematic approach to find the most appropriate configuration and as a result the time and the cost of conceptual design can be considerably reduced.

In this paper four different models which have been presented to analyze the penetration of projectile into semi-infinite targets are compared and contrasted. Tate and Alekseevskii's models are considered as the basic reference models. Vahedi's model is particularly well suited in design situations. Luk's model uses conservation laws and considers the effect of mushrooming while penetrating into target and Walker's model considers the transient phenomena in penetration process. The results related to these models are compared with experimental data and some recommendations are presented.

In this paper, opening mode stress intensity factor (SIF) for edge cracks has been obtained by means of nondestructive optical technique of digital shearography. The resulting fringes were simulated by both analytical relations and finite element method (FEM). Then shearographic relations and linear elastic fracture mechanics relations were incorporated to develop an algorithm to determine K1 To utilize the advantage of "whole field" shearography and to minimize random experimental errors, the least squares method is used to obtain SIF. The comparison of fringes, as well as shearography and empirical K1 values, shows good agreements between simulation and experimental results and proves the credibility of experimental fringes and potentials of this non-destructive method in measurement applications.