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Ovesy H.R.,Amirkabir University of Technology | Fazilati J.,Astronautics Research Institute
Composite Structures | Year: 2014

The parametric instability regions of laminated composite plate and cylindrical shells subjected to non-uniform in-plane axial end-loadings are studied. The static as well as varying parts of the end-loading assumed to vary according to parabolic distribution in the width of the panel. The dynamic instability of panels has been investigated by using a developed finite strip method (FSM). The problem has been formulated on the basis of principle of virtual work. The effects of loading distribution as well as boundary conditions and static loading on the instability regions of load frequency are studied by applying Bolotin's first order approximation. In order to demonstrate the capabilities of the developed formulations and methods in predicting the structural parametric dynamic behavior, some representative results are obtained and compared with those in the literature wherever available. © 2013 Elsevier Ltd. Source


Tahsini A.M.,Astronautics Research Institute
Applied Mechanics and Materials | Year: 2014

The performance of the magnetoplasmadynamic thruster is predicted using numerical simulation. The thruster mode is self induced magnetic field with cylindrical electrodes. The dependence of the thrust level, specific impulse, and the mass flow rate in different total electric currents is investigated. The AUSM+ scheme is utilized to develop a numerical procedure and the accurate method is used to simulate the propellant injection rate. Besides the performance curves prediction, the results show the importance of the effect of inlet modeling on the thruster's actual specific impulse. © (2014) Trans Tech Publications, Switzerland. Source


Kiani F.,Astronautics Research Institute | Javadi K.,Sharif University of Technology
Journal of Turbulence | Year: 2016

This study was conducted to investigate the flow structures of turbulent flow passing over a short finite cylinder in which a rigid flag is attached to the rear of the cylinder, in wake region. The length-to-diameter ratio of the cylinder was chosen to be L/D = 2, whereas the rigid flag had a width-to-diameter ratio of W/D = 1.5. Wall-adapted large-eddy simulation (LES-WALE) was used to resolve unsteady turbulent flow structures. The far field Reynolds number based on cylinder diameter was chosen to be 20,000. The results were compared with the regular case wherein no flag was attached to the cylinder. Results revealed that the flow pattern behind the cylinder with flag was totally different in comparison with the regular case one. However, top free end of the cylinder was not influenced by the flag in contrast with the wake region. At far downstream from the cylinder, most of the flow structures in both cases appeared the same. The horseshoe vortices in both cases appeared to be an unsteady phenomenon, with slightly different patterns. Moreover, in the case of flag attachment, the pressure coefficient was smaller than that of with no flag. Finally, it was shown that the main and secondary Strouhal numbers locations were different in both cases. © 2016 Taylor & Francis Source


Kamali Moghadam R.,Astronautics Research Institute | Javadi K.,Sharif University of Technology | Kiani F.,Astronautics Research Institute
Journal of Applied Fluid Mechanics | Year: 2016

Three-dimensional unsteady flow field around a finite circular cylinder standing in a flat-plate boundary layer is studied. For this purpose, two different numerical turbulence approaches as wall adapted local eddyviscosity LES (LES-WALE) and the zonal hybrid RANS-LES approach of Detached-Eddy Simulation (Zonal-DES) are used. Analysis is carried out for a finite circular cylinder with diameter of D = 3 mm and length-to-diameter ratio of L/D=6 which leads to the Reynolds number 2×104. Numerical simulation has been performed based on the LES-WALE and Zonal-DES turbulence models using coarse and fine grids. Ability and accuracy of two models in capturing the complex physics of present phenomenon are investigated by comparing their results with each other and validated experimental results. Also, effect of several important parameters such as time-averaged pressure coefficient, velocity, vortex shedding frequency and performance of the LES-WALE and Zonal-DES turbulence models are studied. Source


Tahsini A.M.,Astronautics Research Institute | Tadayon Mousavi S.,Astronautics Research Institute
International Journal of Hydrogen Energy | Year: 2015

The purpose of this paper is to investigate the effect of impinging oblique shock on combustion efficiency of hydrogen injection into the supersonic cross-flow. The two-dimensional finite volume solver is developed to simulate the reacting flow, and the one-equation Spalart-Allmaras turbulence model is implemented to capture the turbulent flow characteristics. The impinging oblique shock is produced by a wedge that is located in the upper boundary of the flow field. Finding the best effective parameters on the combustion efficiency may lead to optimize the supersonic combustion chambers, from technological viewpoints. The variation of combustion efficiency versus various induced shock's collision positions with bottom wall in related to the fuel injection location is presented. In addition, the effect of induced shock strength on combustion process is investigated by changing the wedge's angle. Augmentation an additive, H2O2, to the fuel is the other parameter whose effect on combustion characteristics is studied in the disturbed field by impinging oblique shock. Finally, the effects of fuel injection angle as a predominant factor in flow and combustion features is illustrated in this paper. The results show that the shock impinging upstream of the injection slot, tilting the fuel jet to the upstream, increasing the oblique shock strength, and using hydrogen peroxide in fuel stream can effectively increase the combustion efficiency. © 2015 Hydrogen Energy Publications, LLC. Source

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