Scientia Iranica
Volume:23 Issue: 6, 2016

In this study, e ect of di erent slip mechanisms that can produce a slip velocity between nanoparticles and base fluid in a nano fluid flow eld has been investigated numerically. A two-phase Euler-Lagrange approach was applied to simulate heat transfer characteristics of di erent nanoparticles in a straight tube under laminar flow condition. Eff ect of di erent mechanisms such as thermophoresis, Brownian di usion, and Sa man lift force on convective heat transfer was investigated and discussed. It is noticed that only Brownian di usion and thermophoresis are important slip mechanisms in nano fluids. In di erent nano fluids, e ect of Brownian di usion and thermophoresis on convective heat transfer is di erent. While e ect of Brownian di usion is more important in CuO-water nano fluid, thermophoresis is the main slip mechanism in Al2O3-water nano fluid.

In this article, we investigate the double di usive flow of a viscoelastic fluid on a stretching paper with convective boundary condition under the in fluence of thermal-di usion and di usion-thermo e ects, thermal radiation, internal heat generation or absorption, chemical reaction, and thermal radiation. The governing boundary layer equations are analytically solved by using Homotopy Analysis Method (HAM). Variations of the velocity, concentration, and temperature pro les for di erent values of physical parameters are graphically displayed and discussed. Numerical results of the local Sherwood number and the local Nusselt number are also tabulated. It is observed that the local Nusselt number increases on increasing the radiation parameter. The local Sherwood number increases on increasing the chemical reaction parameter.

The aim of this paper is to gure out the flow and heat problem of twodimensional steady axisymmetric laminar mixed-convection boundary-layer flow of Sisko fluid model along a stretching cylinder in a thermally strati ed medium. The similarity transformations are used to reduce coupled partial di erential equations to ordinary di erential equations. To solve these equations, a numerical approach called shooting method has been used for the computation of di erent physical parameters of velocity and temperature eld, respectively. The dependence of skin friction and Nusselt number has been analyzed in details in tables.

In this paper, the in-house code based on the smoothed particle hydrodynamics is proposed to simulate a fluid-solid interaction (FSI) problem. This method is a Lagrangian, mesh-free method and it has a high ability to capture the free surface in two phase flows and also the interface in FSI problems. To compare ofweakly compressible SPH (WCSPH) and incompressible SPH (ISPH) schemes, fluid flow under a hypo-elastic gate is simulated in solid and fluid domains with both methods. At first fluid domain is simulated with ISPH method and solid domain is solved with WCSPH scheme. Another simulation is done with both fluid and solid parts solved with WCSPH method. The results of both methods are in a good agreement with each other and also with other researcher’s results. So it is concluded that it is easier to model the fluid flow with ISPH scheme and the solid part with WCSPH in coupling fluid-solid interaction problems with a good accuracy.

In this paper, the large amplitude free vibration of magnetoelectroelastic curved panels is investigated. The panel is considered to be simply-supported on all edges and the magnetoelectroelastic body is subjected to the electric and magnetic fields along direction. To obtain the governing equations of motion, the Donnell shell theory and the Maxwell equations for electrostatics and magnetostatics are used. The nonlinear partial differential equations of motion are reduced to a single nonlinear ordinary differential equation by introducing trail functions for displacements and rotations and then applying the Galerkin method. The resulting equation is solved by multiple time scales perturbation method. Some numerical examples are presented to validate the study and to investigate the effects of several parameters such as the geometry of the panel and the magnetoelectric boundary conditions on the vibration behavior of these smart panels.

Heat pipes are important cooling devices which are widely used to transfer heat loads. In this paper thermal performance of a novel type of sintered wick heat pipe, namely, partly sintered wick heat pipe has been investigated. The heat pipe was filled with degassed water and acetone, as working fluids, and effects of filling ratio, orientation and heat inputs were tested. Moreover, conditions at which dry-out occurs were presented. Results showed that the best filling ratio for both working fluids is 20%. The heat pipe filled with water has better thermal performance compared with acetone, so that thermal resistances of the 20% water-filled heat pipe are approximately 7%, 27%, and 75% lower than those of the 20% acetone-filled one in the vertical, horizontal, and vertical reverse modes, respectively. This novel type of sintered wick heat pipe has good thermal performance in the horizontal mode and can be used in no-gravity conditions, i.e. space applications.

Emulsi ed fuel is one of the main strategies to substitute the conventional fossil fuel for the purpose of emission control and enhancement of fuel eciency. Accordingly, non-reacting spray characteristics of water-in-Heavy Fuel Oil (HFO) emulsion are numerically investigated in the present study via CFD analysis. Three di erent volumetric percentages of water in HFO are investigated and compared with pure HFO. E ects of four di erent injection pressures on injected fuel spray characteristics are studied. Moreover, in fluences of three di erent ambient back pressures and two ambient temperatures are considered. For these purposes, the characteristics of spray penetration, cone angle, volume, and SMD are evaluated through the analyses of non-dimensional numbers. For modeling the interaction of the fuel discrete phase and the gaseous continuous phase, Eulerian- Lagrangian multiphase formulation in OpenFOAM CFD toolbox is implemented. Fuel droplet tracking in Lagrangian scheme is applied by Lagrangian Particle Tracking method. Also, KH-RT as a hybrid breakup model for liquid fuel core breakup and standard model of k - Ɛ « in RANS for turbulence modeling are utilized. Numerical results are validated against existing experimental data with suitable accordance. Longer spray penetration length, larger cone angle, and greater spray volume are achieved for the emulsi ed fuels.

This study numerically investigates uid ow and heat transfer enhancement of a two-dimensional developing laminar ow in an axisymmetric pipe with partially lled porous material attached to the wall. The eects of porous layer in the range of 0 ≤δ/ R

The purpose of this paper is to investigate the effects of magnetohydrodynamics peristaltic flow of Walter''s B fluid in an inclined asymmetric channel under the influence of slip conditions. The effects of heat and mass transfer are also taken into account. Analytical solutions of nonlinear coupled equations are obtained by regular perturbation method. Graphs for different flow parameters of interest are sketched and analyzed. It is observed that the absolute value of shear stress and heat transfer coefficient decreases by increasing the magnetic parameter whereas with the increase of magnetic parameter, the concentration decreases. Opposite behavior has been noted for temperature and heat transfer coefficient at upper and lower walls against the various values of Prandtl number, Eckert number, slip parameter and material constant of Walter''s B fluid. Oscillatory behavior of heat transfer coefficient is observed which is due to propagation of peristaltic waves along the walls of the channel.

The setting of rolling schedule in tandem cold mill is one of the most crucial content in rolling process, which will have a direct impact on product quality and production efficiency. According to the actual requirements in the rolling process, a multi-objective function based on influence function method was built. The objective function was aimed specially at thin gauge strip and solved by Tabu search algorithm. Meanwhile, in order to avoid the strip slipping by the reduction of friction coefficient, the tension schedule was corrected according to the rolling length of work roll. The proposed optimization method has been applied successfully to a 1450mm 5-stand tandem cold mill. Application results show that the optimized rolling schedules are more close to the actual requirements and the flatness quality is improved greatly.

Wells turbine is a promising self-rectifying device in the eld of ocean wave energy conversion. This study presents an Entropy Generation Analysis (EGA) of isothermal flow through a monoplane Wells turbine. The numerical computation has performed by solving the steady, incompressible, and three-dimensional Reynolds- Averaged Navier-Stokes (RANS) equations with RNG k 􀀀 « turbulence model in a noninertial reference frame rotating with the turbine rotor. Then, local entropy generation rates, related to viscous dissipation around rotor blades, were calculated from the velocity elds. The results indicate that separation and boundary-layer interaction have a direct e ect on the entropy generation. The blade entropy generation decreases from hub to tip and from leading edge to trailing edge in suction surface. Also, the result of comparison shows that the point of minimum entropy generation coincides with the point of maximum rst law eciency of thermodynamics. The results prove that viscous entropy generation distribution provides designers with useful information about the causes of flow irreversibilities. Future monoplane Wells turbine designs should concentrate essentially on optimizing the blade geometry.

The hybrid localization using Angle Of Arrival (AOA) and Di erential Received Strength Signal Indicator (DRSSI) of an RF source with unknown power and Non- Line-Of-Sight (NLOS) condition has been proven to be advantageous compared to using each method separately. In this paper, the initial hybrid method, which was implemented using particle lters due to the multi-modal/non-Gaussian nature of localization in NLOS condition, has been replaced by a multi-step Gaussian ltering approach which provides similar accuracy with better performance. This has been done using DRSSI input in the rst step of the ltering to determine the linearization point, and then using AOA and DRSSI inputs together in the second step of the ltering to improve the localization accuracy. The proposed method has been implemented using Extended Kalman lter and Unscented Kalman lter. The simulation results show that the accuracy of the multi-step Gaussian ltering is comparable to the particle ltering approach with much lower computational load that is important for online localization of several RF sources. Furthermore, the e ects of uncertainty on the propagation parameters have been studied to show that the robustness of the multi-step Gaussian ltering to the uncertainties is comparable to the particle lter approach.

This paper reports on a numerical and experimental investigation of a variable-sweep morphing wing for an unmanned aerial vehicle (UAV) whereby the area and the aspect ratio of the wing can change while its overall configuration is kept nearly unchanged. The numerical results were obtained using computational fluid dynamics (CDF) and the experimental data from a low-speed wind tunnel test at the speeds of 50, 60, and 70 m/s. The extent of change in the sweep angle of the morphing wing relative to the base wing is 12 degrees (i.e. 36%). The results of this study show that lift coefficient, lift curve slope, drag coefficient and the aerodynamic efficiency of the model wing decrease as the sweep angle increases. According to experimental results, the maximum reduction in the drag coefficient of the morphing wing is 6.1% as the sweep angle increases from 33 to 45 deg. Also, the maximum changes in the aerodynamic efficiency of the model with sweep angle changing from 33 to 45 degrees occur at 6 degree angle of attack, which is equal to 11.6%. With changing the wing sweep, the maximum change of flight range and endurance were found to be 8.77 and 7.15%, respectively.