جستجوی مقالات مرتبط با کلیدواژه « suction » در نشریات گروه « برق »

In recent decades, reverse flow analysis in mixed convection flow has attracted the attention of many researchers owing to its applications in the design of medical and engineering systems. The presence of reverse flow is unfavorable in many respects; therefore, it is crucial to find values of critical parameters affecting the reverse flow to eliminate it. In this paper, the thermal and hydrodynamic behavior of MWCNT-Fe3O4 hybrid nanofluid is explored in a vertical cylindrical annulus and in the adjacency of radial magnetic field by achieving the results of the exact solution. Furthermore, the effective factors on the reverse flow are investigated, considering the effects of wall movement and suction/injection on it. The range of changes of the governing parameters includes constant velocity of cylinders’ walls A=0−10, B=0−10, Mixed convection parameter η=-1500−1500, dimensionless temperature difference ratio ξ=0−1, Hartman number Ha=0−50, Suction/injection S=-6−6, nanocomposite particles concentration φ=0−0.3% and radios ratio λ=2−10. The results reveal that hybrid nanofluid enhances the heat transfer rate. Moreover, by changing the above-mentioned parameters and selecting the appropriate values for them, the flow, heat transfer and occurrence of reverse flow can be optimally controlled. Meanwhile, such parameters as Ha, S and ξ perform better in eliminating reverse flow.

An extension of the slip line theory to unsaturated soils is presented and applied to the problem of stability of slopes in unsaturated soils. The matric suction is then introduced and implemented in governing equations by the well-known Bishop effective stress concept. In this regard, the van Genuchten model is utilized to estimate the effective stress parameter required for the computation of the effective stress. The influence of the soil matric suction on the stability of slopes has been investigated for a variety of soils under steady state evaporation and infiltration, i.e., the distribution of the matric suction was assumed to remain constant with time. In addition, a measure of stability in terms of some factor of stability has been introduced.

Soil deposits may experience different hydraulic states in terms of suction (ψ) and degree of saturation (Sr) while subjected to large strain caused by dynamic loading during earthquakes. This phenomenon is investigated by considering the effects of initial ψ, initial Sr, sample preparation method, drainage condition, and cycle number (N) on dynamic properties. Shear modulus (G) and damping ratio (D) are specifically studied for an unsaturated sand using a modified cyclic simple shear device for all zones of soil water retention curve (SWRC). Results revealed the relative significance of both ψ and Sr in relation to SWRC on observed trends in G and D. Through analyzing some results from the literature, it was shown that most of the data follow a sigmoid function in the plane of normalized stiffness (G/Gsat) versus suction normalized to the air entry value. It was also revealed that minimum damping is not in conjugation with maximum stiffness due to the contribution of other mechanisms in damping like inter-particle water lubrication. Comparison between results of two testing methods indicated a notable influence of initial fabric on G. Furthermore, the overall trends in G and D against N are marginally influenced by initial ψ and Sr.

The effects of viscous dissipation and convective boundary condition on the two-dimensional convective flow of a second grade liquid over a stretchable surface with suction/injection and heat generation are investigated. The governing partial differential equations are reduced into a dimensionless coupled system of nonlinear ordinary differential equations by appropriate similarity transformation. Then, they are solved analyticallyby homotopy analysis method (HAM) and by numerically with fourth order Runge-Kutta method with shooting technique. The HAM and numerical results of the local skin friction and local Nusselt number are compared for various emerging parameters. It is found that the momentum boundary layer thickness grows with rising the values of the viscoelastic parameter.

Shock Control Bump (SCB) reduces the wave drag in transonic flight. In high Mach transonic flows, the boundary layer separation downstream the bump, induced by the shock wave, results in the poor performance of the SCB. To control the boundary layer separation and to reduce the wave drag for two transonic airfoils, RAE-2822 and NACA-64A010, we investigate the application of two conventional flow control methods, i.e. suction and blowing, to be added to the SCB. An adjoint gradient based optimization algorithm is used to find the optimum shape and location of SCB. The performance of both hybrid suction/SCB (HSS) and hybrid blowing/SCB (HBS) is a function of the sucked or injected mass flow rate, and their position. A parametric study is performed to find the near optimum values of the aerodynamic coefficients and efficiency. A RANS solver is validated and used for this flow analysis. This study shows that both HSS and HBS methods considerably improve the aerodynamic efficiency (L/D), while the HBS method is more effective in control of the shock wave/boundary layer interaction. Using HSS method, the aerodynamic efficiencies of these two airfoils are increased by, respectively, 8.6% and 3.9%, respect to the airfoils with optimized bumps. For HBS configuration, improvements are respectively 13.5% and 9.0%. The best non-dimensional mass flow rate for suction is found to be around 0.003 for both airfoils, and for blowing this is about 0.0025 for RAE-2822 airfoil and about 0.002 for NACA-64A010. The best location for suction and blowing are found to be, respectively, right before and after the SCB.

Based on the concept of independent stress state variables to consider the impact of unsaturated conditions, an elasto-plastic critical state constitutive model for saturated and unsaturated interfaces is introduced in this paper. The proposed model is capable of predicting many characteristics of unsaturated interface behavior, such as the dependence of initial tangent modulus, peak shear stress, dilatancy, and ultimate strength on matric suction, net normal stress, and the interface state measured with respect to the critical state line. To this aim, two distinct yield mechanisms are employed in the model. While change in stress ratio generates plastic deformation in the first mechanism, plastic deformations are due to an increase in net normal stress, decrease in matric suction, or both, in the second mechanism. The presence of appropriate state dependent ingredients enables the model to provide realistic predictions over a wide range of variations of density, net normal stress, and matric suction. By direct comparison of the model predictions with experimental data, the predictive capacity of the proposed model is evaluated.