Table of Content

01 December 2014, Volume 35 Issue 12

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Articles

Lattice Boltzmann simulations of turbulent shear flow between parallel porous walls

Zheng TANG;Nan-sheng LIU;Yu-hong DONG

2014, 35(12):  1479-1494.  doi:10.1007/s10483-014-1885-6

Abstract ( 422 )   HTML   PDF (2061KB) ( 133 )  

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The effects of two parallel porous walls are investigated, consisting of the Darcy number and the porosity of a porous medium, on the behavior of turbulent shear flows as well as skin-friction drag. The turbulent channel flow with a porous surface is directly simulated by the lattice Boltzmann method (LBM). The Darcy-Brinkman-Forcheimer (DBF) acting force term is added in the lattice Boltzmann equation to simulate the turbulent flow bounded by porous walls. It is found that there are two opposite trends (enhancement or reduction) for the porous medium to modify the intensities of the velocity fluctuations and the Reynolds stresses in the near wall region. The parametric study shows that flow modification depends on the Darcy number and the porosity of the porous medium. The results show that, with respect to the conventional impermeable wall, the degree of turbulence modification does not depend on any simple set of parameters obviously. Moreover, the drag in porous wall-bounded turbulent flow decreases if the Darcy number is smaller than the order of O(10^-4) and the porosity of porous walls is up to 0.4.

Predictive model for stage-discharge curve in compound channels with vegetated floodplains

Chao LIU;Xing-nian LIU;Ke-jun YANG

2014, 35(12):  1495-1508.  doi:10.1007/s10483-014-1884-6

Abstract ( 435 )   HTML   PDF (512KB) ( 139 )  

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The governing equation of the discharge per unit width, derived from the flow continuity equation and the momentum equation in the vegetated compound channel, is established. The analytical solution to the discharge per unit width is presented, including the effects of bed friction, lateral momentum transfer, drag force, and secondary flows. A simple but available numerical integral method, i.e., the compound trapezoidal formula, is used to calculate the approximate solutions of the sub-area discharge and the total discharge. A comparison with the published experimental data from the U.K. Flood Channel Facility (UK-FCF) demonstrates that this model is capable of predicting not only the stage-discharge curve but also the sub-area discharge in the vegetated compound channel. The effects of the two crucial parameters, i.e., the divided number of the integral interval and the secondary flow coefficient, on the total discharge are discussed and analyzed.

Hall and ion slip effects on peristaltic flow and heat transfer analysis with Ohmic heating

S. ASGHAR;Q. HUSSAIN;T. HAYAT;F. ALSAADI

2014, 35(12):  1509-1524.  doi:10.1007/s10483-014-1881-6

Abstract ( 553 )   HTML   PDF (1706KB) ( 112 )  

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The peristaltic transport of a magnetohydrodynamic (MHD) fluid is examined for both symmetric and asymmetric channels. Hall and ion slip effects are taken into account. The heat transfer is analyzed by considering the effects of viscous and Ohmic dissipations. The relevant flow problems are first modeled, and then the closed form solutions are constructed under the assumptions of long wavelength and low Reynolds number. The solutions are analyzed through graphical illustration. It is noted that the velocity increases but the temperature decreases with the increases in the Hall and ion slip parameters. The axial pressure gradient is less in magnitude in the presence of Hall and ion slip currents. The Hall and ion slip effects are to decrease the maximum pressure against which peristalsis works as a pump. The free pumping flux decreases with the increases in the Hall and ion slip parameters. The increases in the Hall and ion slip parameters result in an increase in the size of the trapped bolus.

MHD effect of mixed convection boundary-layer flow of Powell-Eyring fluid past nonlinear stretching surface

S. PANIGRAHI;M. REZA;A. K. MISHRA

2014, 35(12):  1525-1540.  doi:10.1007/s10483-014-1888-6

Abstract ( 568 )   HTML   PDF (1130KB) ( 118 )  

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Sufficient conditions are found for the existence of similar solutions of the mixed convection flow of a Powell-Eyring fluid over a nonlinear stretching permeable surface in the presence of magnetic field. To achieve this, one parameter linear group transformation is applied. The governing momentum and energy equations are transformed to nonlinear ordinary differential equations by use of a similarity transformation. These equations are solved by the homotopy analysis method (HAM) to obtain the approximate solutions. The effects of magnetic field, suction, and buoyancy on the Powell-Eyring fluid flow with heat transfer inside the boundary layer are analyzed. The effects of the nonNewtonian fluid (Powell-Eyring model) parameters ε and δ on the skin friction and local heat transfer coefficients for the cases of aiding and opposite flows are investigated and discussed. It is observed that the momentum boundary layer thickness increases and the thermal boundary layer thickness decreases with the increase in ε whereas the momentum boundary layer thickness decreases and thermal boundary layer thickness increases with the increase in δ for both the aiding and opposing mixed convection flows.

On flow characteristics of liquid-solid mixed-phase nanofluid inside nanochannels

H. AMINFAR;N. RAZMARA;M. MOHAMMADPOURFARD

2014, 35(12):  1541-1554.  doi:10.1007/s10483-014-1889-6

Abstract ( 533 )   HTML   PDF (2603KB) ( 85 )  

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The atomic behavior of liquid-solid mixed-phase nanofluid flows inside nanochannels is investigated by a molecular dynamics simulation (MDS). The results of visual observation and statistic analysis show that when the nanoparticles reach near each other, the strong interatomic force will make them attach together. This aggregation continues until all nanoparticles make a continuous cluster. The effect of altering the external force magnitude causes changes in the agglomeration rate and system enthalpy. The density and velocity profiles are shown for two systems, i.e., argon (Ar)-copper (Cu) nanofluid and simple Ar fluid between two Cu walls. The results show that using nanoparticles changes the base fluid particles ordering along the nanochannel and increases the velocity. Moreover, using nanoparticles in simple fluids can increase the slip length and push the near-wall fluid particles into the main flow in the middle of the nanochannel.

MHD flow of power-law fluid on moving surface with power-law velocity and special injection/blowing

Xue-hui CHEN;Lian-cun ZHENG;Xin-xin ZHANG

2014, 35(12):  1555-1564.  doi:10.1007/s10483-014-1887-6

Abstract ( 481 )   HTML   PDF (228KB) ( 89 )  

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The problem of magnetohydrodynamic (MHD) flow on a moving surface with the power-law velocity and special injection/blowing is investigated. A scaling group transformation is used to reduce the governing equations to a system of ordinary differential equations. The skin friction coefficients of the MHD boundary layer flow are derived, and the approximate solutions of the flow characteristics are obtained with the homotopy analysis method (HAM). The approximate solutions are easily computed by use of a high order iterative procedure, and the effects of the power-law index, the magnetic parameter, and the special suction/blowing parameter on the dynamics are analyzed. The obtained results are compared with the numerical results published in the literature, verifying the reliability of the approximate solutions.

Packing induced bistable phenomenon in granular flow: analysis from complex network perspective

Mao-bin HU;Qi-yi LIU;Wang-ping SUN;Rui JIANG;Qing-song WU

2014, 35(12):  1565-1572.  doi:10.1007/s10483-014-1886-6

Abstract ( 324 )   HTML   PDF (2345KB) ( 84 )  

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The effects of packing configurations on the phase transition of straight granular chute flow with two bottlenecks are studied. The granular flow shows a diluteto-dense flow transition when the channel width is varied, accompanied with a peculiar bistable phenomenon. The bistable phenomenon is induced by the initial packing configuration of particles. When the packing is dense, the initial flux is small and will induce a dense flow. When the packing is loose, the initial flux is large and will induce a dilute flow. The fabric network of granular packing is analyzed from a complex network perspective. The degree distribution shows quantitatively different characteristics for the configurations. A two-dimensional (2D) packing clustering coefficient is defined to better quantify the fabric network.

Effects of size-dependent elasticity on stability of nanotweezers

A. FARROKHABADI;A. KOOCHI;A. KAZEMI;M. ABADYAN

2014, 35(12):  1573-1590.  doi:10.1007/s10483-014-1880-6

Abstract ( 392 )   HTML   PDF (445KB) ( 123 )  

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It is well-recognized that the electromechanical response of a nanostructure is affected by its element size. In the present article, the size dependent stability behavior and nanotweezers fabricated from nanowires are investigated by modified couple stress elasticity (MCSE). The governing equation of the nanotweezers is obtained by taking into account the presence of Coulomb and intermolecular attractions. To solve the equation, four techniques, i.e., the modified variational iteration method (MVIM), the monotonic iteration method (MIM), the MAPLE numerical solver, and a lumped model, are used. The variations of the arm displacement of the tweezers versus direct current (DC) voltage are obtained. The instability parameters, i.e., pull-in voltage and deflection of the system, are computed. The results show that size-dependency will affect the stability of the nanotweezers significantly if the diameter of the nanowire is of the order of the length scale. The impact of intermolecular attraction on the size-dependent stability of the system is discussed.

Dynamic stress concentrations in thick plates with two holes based on refined theory

Chuan-ping ZHOU;Chao HU;F. MA;Dian-kui LIU

2014, 35(12):  1591-1606.  doi:10.1007/s10483-014-1883-6

Abstract ( 510 )   HTML   PDF (369KB) ( 71 )  

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Based on complex variables and conformal mapping, the elastic wave scattering and dynamic stress concentrations in the plates with two holes are studied by the refined dynamic equation of plate bending. The problem to be solved is changed to a set of infinite algebraic equations by an orthogonal function expansion method. As examples, under free boundary conditions, the numerical results of the dynamic moment concentration factors in the plates with two circular holes are computed. The results indicate that the parameters such as the incident wave number, the thickness of plates, and the spacing between holes have great effects on the dynamic stress distributions. The results are accurate because the refined equation is derived without any engineering hypothese.

Aerodynamic mechanism of forces generated by twisting model-wing in bat flapping flight

Zi-wu GUAN;Yong-liang YU

2014, 35(12):  1607-1618.  doi:10.1007/s10483-014-1882-6

Abstract ( 426 )   HTML   PDF (544KB) ( 127 )  

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The aerodynamic mechanism of the bat wing membrane along the lateral border of its body is studied. The twist-morphing that alters the angle of attack (AOA) along the span-wise direction is observed widely during bat flapping flight. An assumption is made that the linearly distributed AOA is along the span-wise direction. The plate with the aspect ratio of 3 is used to model a bat wing. A three-dimensional (3D) unsteady panel method is used to predict the aerodynamic forces generated by the flapping plate with leading edge separation. It is found that, relative to the rigid wing flapping, twisting motion can increase the averaged lift by as much as 25% and produce thrust instead of drag. Furthermore, the aerodynamic forces (lift/drag) generated by a twisting plate-wing are similar to those of a pitching rigid-wing, meaning that the twisting in bat flight has the same function as the supination/pronation motion in insect flight.