جستجوی مقالات مرتبط با کلیدواژه « plasma » در نشریات گروه « مکانیک »

In the last decade, plasma actuators have been recognized as a subset in the field of active flow control devices. As research on plasma actuators continues to evolve, computational modeling is needed to complement actuators research. In this study, the Suzen-Huang model is chosen because of its ability to simulate the charge density and Lorentz volume force. The use of this model in various fields, including aerodynamics, has led to many applications, but due to the complexity of simulating the effects of plasma, it is mostly focused on the simulation of its force effects. In the field of combustion and the use of plasma in this state, most of the activities and investigations are seen in experimental works. In this work, based on the Susen-Hong model, it is tried to simulate the plasma force effect of the dielectric barrier discharge type in the combustion environment and its role in better mixing of fuel and oxidant. It should be noted that in this study, the mild combustion was not simulated and only the effect of plasma in a mild burner was investigated. The results are promising and indicate the positive effect of plasma in better mixing of fuel and oxidizer before combustion.
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Plasma actuator is an active flow control tool, which has been evaluated by the aerodynamic researchers since last decade due to its simple structure, light weight, low energy consumption, and high time response. In this paper effects of plasma on aerodynamic behavior of a rocket at different flight conditions is numerically investigated. Results of plasma effects or variation of attack angle, Mach number, and flight altitude on the drag and lift coefficients are evaluated. Applying plasma increases the vertical velocity under the rocket canards which leads to higher pressures and therefore higher pressure difference and forces are applied on the rocket canards which improves their functionality. Drag and lift coefficients are both increased due to the plasma, but the aerodynamic efficiency (lift to drag ratio) is increased by increasing potential difference. Results shows that plasma effect is reduced with increasing of angle of attack and increased with the flight altitude and aerodynamic efficiency is changed between %3 and %60 by applying plasma.

In this study, a cold atmospheric He plasma jet is investigated. The jet is of dielectric barrier discharge type, consisting of a dielectric tube with two metal ring electrodes. The continuity, momentum and energy conservation equations as well as the Poisson equation for obtaining the potential and the electric field, accompanied with the ideal gas laws, are used for the simulation. The results show that the electron and ion densities, potential and space charge field, internal energy, temperature and velocity of the electrons increase with time. Moreover, the increment of the plasma length and its forward propagation along the jet axis with time is also observed. Therefore, it is expected that the values of the mentioned quantities increase with time, which results in the increment of the plasma jet length.

In this paper, the method of second harmonic generation of longitudinal and transverse waves in cold, low-density and uniform non-magnetic plasma is invistigated, when a short pulse laser or lidar is propagated in the plasma medium and collision effects are considered. Also, the effect of external uniform magnetic field on the plasma is studied. The propagation of electromagnetic waves in isotropic plasma can produce odd harmonics, but magnetic field varies isotropic state and produce even harmonics. Using perturbation theory companents of electric field of first and second harmonic are calculated and the effects of successive reflections on the electric field amplitude of first and second harmonics and efficiency of reflection power of second harmonic are investigated. Also, with analysis of government equations the resulas are obtained. Finally, field amplitude of harmonics for zero and first perturbatins for different states are studied and variations of them in term o different parameters are plotted. Also, results and optimom conditions are discussed and some suggestions are offered.

The possibility of workpiece deformation after or during machining due to residual stresses is of crucial importance in precise components. These stresses are induced mainly due to plastic deformation or heat generation during the metal cutting process. Therefore, the magnitude of machining residual stresses is affected by mechanical and thermal stresses. Mechanical stresses depend on the cutting forces and thermal stresses originate from the magnitude of heat generation during cutting action. Therefore, it is expected that machining processes with lower cutting forces and cutting temperatures, will induce lower machining residual stresses as well. Plasma assisted machining is a process that uses a heat source to increase workpiece local temperature and thereby decrease the strength of the material which is to be removed; therefore lower values of cutting forces, temperatures, and residual stresses are expected. In this research work, the effects of undeformed chip temperature, cutting speed, and feed have been investigated on the machining induced residual stresses in the plasma-assisted orthogonal turning of AISI 4140. According to the achieved results, undeformed chip temperature is the most effective parameter on machining residual stresses and by increasing this parameter from 75 to 220˚C, machining induced surface residual stresses became more compressive averagely by 85.30%.