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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.

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

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

At this paper, the thermal behavior of ablative materials as heat shields for reentry vehicles is investigated numerically. A one-dimensional finite difference solver is developed to simulate governing mass and energy equations. Four ablative materials; AVCO 5026-HCG, Carbon-Phenolic, Nylon-Phenolic, and Silica-Phenolic; are considered as a heat shield material for a reentry capsule with the diameter 2.8 meter. A heat flux profile from a simulated trajectory of a reentry capsule is used for investigation the performance and essential thickness of these four ablative materials. The only restriction for this simulation is the ultimate temperature of the backup structure which is beneath the ablative heat shield. At all simulations, the final thickness is defined by reaching the interface temperature, the temperature of the border between the ablative heat shield and solid shell, to 80±0.5 degrees Celsius. In addition, the sensitivity analysis is carried out to investigate the effect of properties variations on Carbon-Phenolic's thickness for this specific heat flux profile. © (2014) Trans Tech Publications, Switzerland.

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.

Tahsini A.M.,Astronautics Research Institute | Tadayon Mousavi S.,Astronautics Research Institute
52nd Aerospace Sciences Meeting | Year: 2014

At This Paper, the accuracy of one equation Spalart-Allmaras turbulence model for prediction of heat transfer and flow characteristic in turbulent confined impinging slot jets upon a flat plate is investigated. A compressible two-dimensional finite volume solver is developed to simulate the flow behavior. Basic form of the Spalart-Allmaras eddy viscosity transport equation in accompanied by the modification that is considered the effect of mean strain rate on turbulent production term are implemented to assess the accuracy of this simple model. Impinging jet flow is simulated at three critical nozzle to plate distances—inside the jet potential core, at the end of jet potential core, and beyond the jet potential core-in order to clarify the model behavior. Results confirm the acceptable prediction of flow characteristics in comparison with simplicity and affordable computational time of this model. In addition, the effect of nozzle to impinging plate distance as a predominant parameter on heat transfer and flow behavior is physically explained. This factor is not obviously illustrated for confined impinging slot jets at literatures. © 2014, American Institute of Aeronautics and Astronautics Inc. All rights reserved.

Marzabadi F.R.,Astronautics Research Institute | Moghaddam R.K.,Astronautics Research Institute
Advanced Materials Research | Year: 2014

Longitudinal dynamic derivatives of an airfoil oscillating in pitching and plunging motions were calculated using variation of pitching moment coefficients with angle of attack in various conditions, based on wind tunnel data. The effect of reduced frequency on variation of longitudinal oscillatory derivatives was investigated, in three different regions of oscillation: before, over and post stall conditions. The results showed that reduced frequency has significant effects on longitudinal oscillatory coefficients in different conditions for both types of oscillations. © (2014) Trans Tech Publications, Switzerland.

Moghadam R.K.,Astronautics Research Institute | Hosseini S.A.,Astronautics Research Institute
Advanced Materials Research | Year: 2014

Two efficient computational procedures based on the boundary layer equations and approximate relations areassessedin prediction of the laminar hypersonic flowfield for both the perfect gas and equilibrium air around the axisymmetric blunt body configurations. For the boundary layer procedure, the boundary layer equationsutilize the integral matrix solution algorithm for the blunt nose and after body region by using a space marching technique. The integral matrix procedure able us to create accurate and smooth results using the minimum grid in the boundary layer and minimize the computational costs. Applying the approximate method creates a robust and efficient code for heating calculations over the blunt bodies which flies in hypersonic regimes. These algorithms are highly appropriate to design of hypersonic reentry vehicles. The effects of real gas on the flowfield characteristics are also studied in two procedures. © (2014) Trans Tech Publications, Switzerland.

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

In the present work, the surface temperature history of a metal shell of the blunt nose of supersonic launch vehicle which is covered by a thermal protection coating is numerically predicted and compared with experimental data. The full Navier-Stokes equations are used to estimate the aerodynamic heat flux during flight, coupled with the governing equations for the thermal protection system to study the erosion rate and temperature variations. The results show the importance of the properties of the coating on accuracy of the numerical predictions. © (2014) Trans Tech Publications, Switzerland.

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.

Entezari M.M.,Astronautics Research Institute | Mohammadi-Amin M.,Astronautics Research Institute
11th World Congress on Computational Mechanics, WCCM 2014, 5th European Conference on Computational Mechanics, ECCM 2014 and 6th European Conference on Computational Fluid Dynamics, ECFD 2014 | Year: 2014

In this paper, the flow between two counter-rotating smooth disks enclosed by a cylinder is investigated numerically for different high Reynolds numbers and different ratios of the rotating speeds of two disks. Numerical predictions are based on standard k-s and RSM model and the results are compared with experimental data i.e. velocity measurements performed at CEA (commissariate al'Energe atomique). The infuences of the rotational Reynolds number and the rotating disk speed ratio are investigated to get knowledge of both the dynamic and the turbulence properties in the Von Karman configuration. It is concluded that turbulence can primarily affect on velocity profile.

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