مجله مکانیک سیالات و آیرودینامیک
سال سوم شماره 2 (تابستان 1393)

In this research ideal Magnetohydrodynamics Equations (MHD) has been solved in a channel of quasi one dimensional plasma flow. Magnetohydrodynamics Equations, including continuity, momentum, Energy and induced magnetic field equations are with the respect of the Gauss magnetic condition. The implemented numerical solution is based on Harten, Lax, Vanleer (HLLD) discontinuities solution methods. Hall effects, ionization process, heat transfer, and viscosity have been neglected in the simulation. Electrical conductivity and permeability of free space has been assumed uniform and constant. Magnetic shock tube has been investigated for verification of applied numerical simulation in MHD flow. Next, a quasi-one dimensional magnetic accelerator has investigated which could be used for the development of magnetoplasmadynamic thruster. The represented non-dimensional results include velocity, magnetic field, density, pressure, and Mach number graph in one dimensional magnetic accelerator have been compared with other references which shows appropriate accuracy of the applied numerical method.

In this study a nonlinear asymmetric instability analysis carried out to study primary atomization of annular liquid sheets emanating from the prefilming airblast atomizer using a perturbation method and potential flow assumption. In this direction، firstly governing equations derived according to potential flow assumption and conservation equations while dynamic and static boundary condition at the interface are considered. The first and second order equation is solved using Mathematica. In order to evaluate the results، model results in 2D geometry compared with results of Jazayeri 2D sheet instability analysis. Then the variation of deduced instability growth rate against wave number، compared with the results of other researchers. At next step an experimental test performed to measure of primary breakup length of an airblast atomizer and the result compared with the primary breakup length which deduced from nonlinear and linear instability analysis. Finally the primary breakup length of nonlinear study compared with a curve، which fitted on experimental results at various we number.

The formation of Ice on a cold surface and its shape، play an important role in some of the various problems. The position of solid surface of ice accretion، its growth shape and the effect of liquid phase on it، are important parameters in the various applications. Difficulty of analytic techniques and expensive of experimental methods encourage the numerical modeling procedures in the investigation of this transient evidence. The enthalpy-porosity technique has been used for material with similar properties in solid and liquid phase usually. This method is improved، introducing functional fluid properties، for a substance with a variable property in this research. This developed model is utilized to modeling of the water freezing in a cavity while it is in the condition of natural convection. Formation of two vortexes and the solid surface perpendicularity on lower wall as observed in experimental tests، is verified the quantity evaluation. Moreover the results show the more accurate data in improved model in compare with experimental data. Average data in shape growth results in 4% improvement in compare with some of utilized recent models.

The manner of spray the fuel has an important effect on stability and convenient mixture of fuel and oxidizer. Swirl injectors because of formation of uniform spray cone and proper distribution of the fuel have been used in many rocket engines at aerospace industries. Formation and development of air core in the interior stream of swirl injectors and simulation of them is complicated. Double base-swirl injectors have better atomization and have more effective and uniform mixture and combustion. Inner stream has an important effect on spray characteristics. In this article we want to simulate liquid film، air core and spray angle in double base swirl injector. Inner stream of swirl injector simulate with two-phase method and we use air for gas-phase and water for liquid-phase and validate our results with experimental results. Because this way is very cheaper and faster rather than experimental studies.

Exergy analysis of a system is a method for recognizing the value and type of system availability against surrounding environment. It also helps to find how macroscopic properties of the system change during a process. This analysis is based on first and second laws of thermodynamics. By exergy analysis proportion of each process in the internal availability transmission and the places of useful energy losses in the system can be determined. In this research exergy analysis of radial flow compressor in the various working conditions is considered. So، the approach for compressor modeling by assumption of one dimensional ideal gas flow is considered. In this method the secondary flow effects and the other real flow losses are added to the model by the appropriate loss coefficients that almost are attained by experimental results. In the one dimensional analysis، compressor components are studied separately and with regard to inlet stagnation properties، passing flow duct geometry and present losses. Thus، the performance characteristics of compressor are estimated with average relative errors of 7 and 10 percent for pressure ratio and efficiency respectively. From the presented results it can be concluded that maximum efficiency location is coincide with location of minimum incidence loss at inducer and this point is transferred to further flow rates by increasing impeller speed.