Current Issue : October - December Volume : 2013 Issue Number : 4 Articles : 6 Articles
This paper presents an improved method for inclusion of system rotation and streamline curvature effects into existing twoequation\r\neddy-viscosity turbulence models. A new formulation for calculation of the turbulence viscosity coefficient, which is\r\nimplemented into the traditional K-E model with a two-layer near-wall treatment in a commercial computational fluid dynamics\r\nsolver, is proposed. In contrast to precious model, the modi??ed rotation rate which appears in the formulation for turbulent viscosity\r\ncoefficient is herein expressed exactly and universally. Thus, it provides an effective alternative for turbulence modeling....
This study experimentally investigates the mechanism of the ignition of the supersonic liquid fuel jet by the visualization. NHexadecane\r\nhaving the cetane number of 100 was used as a liquid for the jet in order to enhance the ignition potential of the\r\nliquid fuel jet. Moreover, the heat column and the high intensity CO2 laser were applied to initiate the ignition. The ignition over\r\nthe liquid fuel jet was visualized by a high-speed digital video camera with a shadowgraph system. From the shadowgraph images,\r\nthe autoignition or ignition of the supersonic liquid fuel jet, at the velocity of 1,186 m/s which is a Mach number relative to the air\r\nof 3.41, did not take place.The ignition still did not occur, even though the heat column or the high intensity CO2 laser was alone\r\napplied. The attempt to initiate the ignition over the liquid fuel jet was achieved by applying both the heat column and the high\r\nintensity CO2 laser. Observing the signs of luminous spots or flames in the shadowgraph would readily indicate the presence of\r\nignitions. The mechanism of the ignition and combustion over the liquid fuel jet was clearly clarified. Moreover, it was found that\r\nthe ignition over the supersonic liquid fuel jet in this study was rather the force ignition than being the auto-ignition induced by\r\nshock wave heating....
The effect of magnetic field on double-diffusive natural convection in a square cavity filled with a fluid-saturated porous medium\r\nis studied numerically. The bottom wall is fully heated at a constant temperature, and the top wall is maintained at a constant cold\r\ntemperature.The right wall is fully salted to a high concentration, while the left wall is fully salted at a lower concentration than the\r\nright one. A magnetic force is applied on the cavity along the gravity force direction. The Darcymodel is used for the mathematical\r\nformulation of the fluid flow through porous media. The governing equations for heat and mass transfer are solved using the finite\r\nvolume method. The governing parameters of the present study are Rayleigh number (Ra), Lewis number (Le), buoyancy ratio (N),\r\nand Hartmann number (Ha). The numerical solutions were studied in the range of -10 = ?? = 10, 0 = Ha = 10, 50 = Ra = 500,\r\nand 10-4 = Le = 10.The results were discussed considering the effect of these parameters on the heat and mass transfer processes.\r\nThe results were presented in terms of streamlines, isotherms, isoconcentration, average Nusselt number, and average Sherwood\r\nnumber for different values of the governing parameters. In general, it has been found that the increase of magnetic force has an\r\neffect to retard the strength of the flow inside the cavity and reduce the heat and mass transfer processes. For high Hartmann\r\nnumber, the flow is almost suppressed....
Field bus system has been successfully introduced into industrial automation. Nowadays, most of the motion control bus is based\r\non the Ethernet physical layer, and all of the new standards are based on the Ethernet physical layer. This paper introduces a new\r\noptimized technology based on motion control bus of the Ethernet physical layer, which includes the prediction mechanism in the\r\narrival of the frames, the retransmissionmechanism in advance, and a new mechanism of independent verification of data segment.\r\nTests show that using the mechanisms in this paper can enhance efficiency and reliability in communication process....
Planetary gear trains (PGTs) are introduced to undergraduate mechanical engineering students in the course of Theory of Machines. The complexity of the traditional methods for analyzing PGTs has kept many from becoming familiar with the capability of PGTs in mechanisms and machine design. In this paper a unified general formulation for simultaneously visualizing velocities, torques, and power flow through a train is presented on a single nomograph. Therefore, the increasing complex mechanical systems, such as automotive transmissions, are much easier to understand. Nomographs of Fundamental Gear Entities (FGEs) are constructed based on the nomographs of their fundamental circuits, without specifying the exact gear dimensions. They are then unified in one system nomograph. Nomographs are promising to provide designers with an efficient tool for the design of geared mechanisms....
In order to study the polymer effect on the behavior of nonlinearities in decaying homogeneous isotropic turbulence (DHIT),\r\ndirect numerical simulations were carried out for DHIT with and without polymers.We investigate the nonlinear processes, such\r\nas enstrophy production, strain production, polymer effect, the curvature of vortex line, andmany others. The analysis results show\r\nthat the nonlinear processes like enstrophy production (and many others) are strongly depressed in regions dominated by enstrophy\r\nas compared to those dominated by strain either in the Newtonian fluid case or in polymer solution case. Polymers only decrease\r\nthe values of these parameters in the strongest enstrophy and strain regions. In addition, polymer additive has a negative effect on\r\nenstrophy and strain production, that is, depression of nonlinearity in DHIT with polymers....
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