جستجوی مقالات مرتبط با کلیدواژه « Numerical study » در نشریات گروه « مکانیک »

In the present study, the influence of the oxidizer preheating temperature and oxygen mass fraction as the effective parameters on the flameless combustion under oxy-syngas, air-syngas, and oxygen-enriched conditions have been investigated. The simulations have been carried out with applying the counter-flow diffusion flame solver using GRI3.0 chemical kinetics. In order to separate the physical and chemical impacts of substituting CO2 with N2, a virtual species (VCO2) has been used with physical properties similar to CO2 without being present in the reactions chain. According to the obtained results, physical and chemical impacts are dominant for lower preheating temperatures and higher preheating temperatures, respectively. The investigation of ignition delay time shows that under oxy-syngas conditions, increasing the H2/CO ratio from 0.25 to 1 and from 1 to 4 leads to a decrease in the axial distance of ignition from 0.4 cm to 0.39 cm and it changes from 0.39 cm to 0.375 cm, respectively. The comparison between the oxygen mole fraction and the inlet preheating temperature indicates that the preheating temperature has a greater effect on the reactive flow structure parameters such as ignition delay and released heat.
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In this research, the internal flow of open-end pressure-swirl atomizer, which has many applications in gas turbine engines and space propulsion, is investigated numerically. A multi-phase fluid volume model is used to simulate the internal flow of the atomizer. Also, due to the nature of the rotational flow inside the atomizer, the RNG k-ε turbulence model was used. Structured mesh has been used to achieve better results. In this research, spray parameters such as liquid film thickness, spray cone angle, discharge coefficient and velocity and pressure distribution contours have been studied. Simulation of an open-end atomizer with an L⁄D = 5 ratio, as well as the use of a structured mesh and the inclusion of kerosene fuel to create conditions close to the operation of a gas turbine, are among the things that differentiate the present study from other studies. The results also show that at a pressure of 0.5 MPa, the time required to reach the fuel in the atomizer used is less than 1.5 milliseconds and the failure of the to spray cone and turn into larger droplets can be observed. The spray angle and discharge coefficient for the studied atomizer were 74.8 and 0.17, respectively.

The most recent proposed technique for drag reduction in hypersonic flow speeds is using the exothermic coating on the blunt nose. This leads the heat addition into the flow field behind the shock wave, and increases the shock-stand-off distance. The variation of the drag force on the flying body using this technique is numerically investigated in the present study. The compressible turbulent flow is simulated around the body to compute the drag force, and to estimate the drag reduction capabilities of this technique. This quantitative analysis makes better insight to evaluate it in operational applications

In the present study, the effect of different projectiles on the carbon and glass fiber reinforced laminated composites is investigated experimentally and numerically. 8 samples of six-layers composite sheets with dimensions of 25×25 cm reinforced with glass and carbon fibers and epoxy resin3001 are subjected to low velocity impact. Also, spherical and semi-spherical steel projectiles of 680 grs weight and 55 mm diameters are used. Drop weight height of projectiles are supposed to be 1 and 1.5 m which leads to equivalent 6.7 and 10 J of impact energy. ANSYS and LSDYNA packages are used for numerical study. Results show that maximum deflection is occurred at the center of laminates for carbon and glass reinforced samples by the spherical projectiles. In addition, it is seen that deflection of carbon and glass laminated composites due to the impact of semi-spherical projectile reduces 18.7% and 34.3% respectively in comparison with the spherical projectile.

When a flying vehicle approaches a surface of water or land, changes occur in the pattern of the fluid flow field around it. This change in flow field eliminates the direct effect on aerodynamics and control of the vehicle. This is more common when the vehicle is landing and taking off, as well as flying at low altitudes, which is called the surface effect. In this research, the phenomenon of surface effect and its effect on aerodynamic coefficients and flow pattern around NACA0012 airfoil in the static incompressible subsonic regime have been investigated numerically and experimentally. Experimental tests were performed in the incompressible subsonic wind tunnel of the Ghadr National Aerodynamics Research Center of Imam Hossein University with a cross-sectional area of 80 by 100 cm. The simulation of the phenomenon is a fixed ground with the minimum possible thickness of the boundary layer in the wind tunnel. Solve the flow field numerically based on Navier Stokes equations along with the Transition-SST viscous model. The impact of the surface effect phenomenon on the change of aerodynamic coefficients has been investigated by considering different distances from the surface in the static state. The pressure distribution on the airfoil surface is measured by an accurate pressure sensor and is due to the surface effect phenomenon at close distances to the surface. The results of the static analysis show an increase in lift force and a decrease in drag force.

In this paper, mixed convection of Bingham fluid between two coaxial cylinders has been studied numerically without using any regularization method. The temperature of the inner rotating circle is higher than the temperature of the outer stationary circle. The finite volume method and non-iterative PISO algorithm have been employed to solve the problem. One of OpenFOAM solver, icoFoam, has been modified for solving the exact Bingham model. After validating the modified solver, it has been used to solve the problem for the following ranges of conditions: Reynolds number, Re=10, Prandtl number, Pr=10, Grashof number, Gr=500, Bingham number, 0≤Bn≤1000, and aspect ratio (AR) of 0.1. The effects of the Bingham number on flow and heat transfer characteristics such as the shape and size of the unyielded regions, streamline contours, the local and mean Nusselt number, and the torque coefficient have been investigated. The mean Nusselt number and the torque coefficient decreases and increases, respectively, when the Bingham number increases. The variation range of the local Nusselt number and dimensionless tangential stress on the inner wall decrease with Bn.

This research represents the dual blanket structure and liquid metal fluid hydrodynamic characteristic under magnetic field. Numerical study of the flow inside the blanket which is separated by separator structure from the shell side is done. This structure is used for both thermal insulation and pressure drop reducing mechanism. As the fluid has electrical conductivity properties, magnetohydrodynamic analysis is also done. In the current study following analyses are done: magnetic field effect, wall electrical conductivity, baffle thickness and its distance from wall in on pressure drop, as well as explaining the behavior of velocity profile under magnetic field changes. According to the result increasing the magnetic field from 0.4 T to 1 T increasing the pressure drop by 4 times the initial value. Also, reducing the electrical conduction in the separating wall from 500 S/m to 5  S/m reduces the pressure drop by 35%. Studies on the different thicknesses of the separator structure in 16 different cases with constant distance between the separator and the wall does not have a significant effect on the pressure drop but by increasing the distance between the separator and the wall the pressure drop will decrease and consequently decreasing in pumping power.