Table of Content

01 June 2014, Volume 35 Issue 6

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Articles

Mode decomposition of nonlinear eigenvalue problems and application in flow stability

Jun GAO;Ji-sheng LUO

2014, 35(6):  667-674.  doi:10.1007/s10483-014-1820-6

Abstract ( 583 )   HTML   PDF (193KB) ( 433 )  

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Direct numerical simulations are carried out with different disturbance forms introduced into the inlet of a flat plate boundary layer with the Mach number 4.5. According to the biorthogonal eigenfunction system of the linearized Navier-Stokes equations and the adjoint equations, the decomposition of the direct numerical simulation results into the discrete normal mode is easily realized. The decomposition coefficients can be solved by doing the inner product between the numerical results and the eigenfunctions of the adjoint equations. For the quadratic polynomial eigenvalue problem, the inner product operator is given in a simple form, and it is extended to an Nth-degree polynomial eigenvalue problem. The examples illustrate that the simplified mode decomposition is available to analyze direct numerical simulation results.

Flow patterns and boundary conditions for inlet and outlet conduits of large pump system with low head

Lei XU;Wei-gang LU;Lin-guang LU;Lei DONG;Zhao-fei WANG

2014, 35(6):  675-688.  doi:10.1007/s10483-014-1821-6

Abstract ( 384 )   HTML   PDF (4027KB) ( 220 )  

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The flow patterns in the inlet and outlet conduits have a decisive effect on the safe, stable, and highly efficient operation of the pump in a large pumping station with low head. The numerical simulation of three-dimensional (3D) turbulence flow in conduits is an important method to study the hydraulic performance and conduct an optimum hydraulic design for the conduits. With the analyses of the flow patterns in the inlet and outlet conduits, the boundary conditions of the numerical simulation for them can be determined. The main obtained conclusions are as follows: (i) Under normal operation conditions, there is essentially no pre-swirl flow at the impeller chamber inlet of an axial-flow pump system, based on which the boundary condition at the inlet conduit may be defined. (ii) The circulation at the guide vane outlet of an axial-flow pump system has a great effect on the hydraulic performance of the outlet conduit, and there is optimum circulation for the performance. Therefore, it is strongly suggested to design the guide vane according to the optimum circulation. (iii) The residual circulation at the guide vane outlet needs to be considered for the inlet boundary condition of the outlet conduit, and the value of the circulation may be measured in a specially designed test model.

Electroosmotic flow of Eyring fluid in slit microchannel with slip boundary condition

Zhen TAN;Hai-tao QI;Xiao-yun JIANG

2014, 35(6):  689-696.  doi:10.1007/s10483-014-1822-6

Abstract ( 674 )   HTML   PDF (264KB) ( 593 )  

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In consideration of the electroosmotic flow in a slit microchannel, the con-stitutive relationship of the Eyring fluid model is utilized. Navier's slip condition is used as the boundary condition. The governing equations are solved analytically, yielding the velocity distribution. The approximate expressions of the velocity distribution are also given and discussed. Furthermore, the effects of the dimensionless parameters, the electrokinetic parameter, and the slip length on the flow are studied numerically, and appropriate conclusions are drawn.

Peristaltic flow of Johnson-Segalman fluid in asymmetric channel with convective boundary condition

H. YASMIN;T. HAYAT;A. ALSAEDI;H. H. ALSULAMI

2014, 35(6):  697-716.  doi:10.1007/s10483-014-1823-6

Abstract ( 586 )   HTML   PDF (969KB) ( 402 )  

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This work is concerned with the peristaltic transport of the Johnson-Segalman fluid in an asymmetric channel with convective boundary conditions. The mathematical modeling is based upon the conservation laws of mass, linear momentum, and energy. The resulting equations are solved after long wavelength and low Reynolds number are used. The results for the axial pressure gradient, velocity, and temperature profiles are obtained for small Weissenberg number. The expressions of the pressure gra-dient, velocity, and temperature are analyzed for various embedded parameters. Pumping and trapping phenomena are also explored.

 

Flow of variable thermal conductivity fluid due to inclined stretching cylinder with viscous dissipation and thermal radiation

T. HAYAT;S. ASAD;A. ALSAEDI

2014, 35(6):  717-728.  doi:10.1007/s10483-014-1824-6

Abstract ( 760 )   HTML   PDF (341KB) ( 834 )  

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The aim of the present study is to investigate the flow of the Casson fluid by an inclined stretching cylinder. A heat transfer analysis is carried out in the presence of thermal radiation and viscous dissipation effects. The temperature dependent thermal conductivity of the Casson fluid is considered. The relevant equations are first simplified under usual boundary layer assumptions, and then transformed into ordinary differential equations by suitable transformations. The transformed ordinary differential equations are computed for the series solutions of velocity and temperature. A convergence analysis is shown explicitly. Velocity and temperature fields are discussed for different physical parameters by graphs and numerical values. It is found that the velocity decreases with the increase in the angle of inclination while increases with the increase in the mixed convection parameter. The enhancement in the thermal conductivity and radiation effects corresponds to a higher fluid temperature. It is also found that heat transfer is more pronounced in a cylinder when it is compared with a flat plate. The thermal boundary layer thickness increases with the increase in the Eckert number. The radiation and variable thermal conductivity decreases the heat transfer rate at the surface.

Numerical well test for well with finite conductivity vertical fracture in coalbed

Yue-wu LIU;Wei-ping OU-YANG;Pei-hua ZHAO;Qian LU;Hui-jun FANG

2014, 35(6):  729-740.  doi:10.1007/s10483-014-1825-6

Abstract ( 578 )   HTML   PDF (2625KB) ( 310 )  

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A new well test model is developed for the hydraulic fractured well in coalbed by considering the following aspects: methane desorption phenomena, finite conductivity vertical fractures, and asymmetry of the fracture about the well. A new parameter is introduced to describe the storage of the fracture, which is named as a combined fracture storage. Another new concept called the fracture asymmetry coefficient is used to define the asymmetry of the fracture about the well. Finite element method (FEM) is used to solve the new mathematical model. The well test type curves and pressure fields are obtained and analyzed. The effects of the combined fracture storage, desorption factor, fracture conductivity, and fracture asymmetry coefficient on the well test type curves are discussed in detail. In order to verify the new model, a set of field well test data is analyzed.

Analysis of realistic rough surface for its globally dominant parameters using continuous wavelets

Yan-hua WU;Hui-ying REN

2014, 35(6):  741-748.  doi:10.1007/s10483-014-1826-6

Abstract ( 435 )   HTML   PDF (1324KB) ( 334 )  

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Continuous Morlet and Mexican hat wavelets are used to analyze a highly irregular rough surface replicated from real turbine blades which are roughened by deposi-tion of foreign materials. The globally dominant aspect ratio, length scale, and orientation of the roughness elements are determined. These parameters extracted from this highly irregular rough surface are important for the future studies of their effects on turbulent flows over this kind of rough surfaces encountered in Washington aerospace and power generating industries.

Electroosmotic oscillatory flow of micropolar fluid in microchannels：application to dynamics of blood flow in microfluidic devices

J. C. MISR;S. CHANDRA;G. C. SHIT;P. K. KUNDU

2014, 35(6):  749-766.  doi:10.1007/s10483-014-1827-6

Abstract ( 497 )   HTML   PDF (511KB) ( 515 )  

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The electroosmotic flow of a micropolar fluid in a microchannel bounded by two parallel porous plates undergoing periodic vibration is studied. The equations for conservation of linear and angular momentums and Gauss's law of charge distribution are solved within the framework of the Debye-Hückel approximation. The fluid velocity and microrotation are assumed to depend linearly on the Reynolds number. The study shows that the amplitude of microrotation is highly sensitive to the changes in the magnitude of the suction velocity and the width of the microchannel. An increase in the micropolar parameter gives rise to a decrease in the amplitude of microrotation. Numerical estimates reveal that the microrotation of the suspended microelements in blood also plays an important role in controlling the electro-osmotically actuated flow dynamics in microbio-fluidic devices.

Oscillations of elastically mounted cylinders in regular waves

Wei SU;Jie-min ZHAN;Yok-sheung LI

2014, 35(6):  767-782.  doi:10.1007/s10483-014-1850-6

Abstract ( 422 )   HTML   PDF (566KB) ( 233 )  

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Under the assumption of potential flow and linear wave theory, a semi-analytic method based on eigenfunciton expansion is proposed to predict the hydrody-namic forces on an array of three bottom-mounted, surface-piercing circular cylinders. The responses of the cylinders induced by wave excitation are determined by the equa-tions of motion coupled with the solutions of the wave radiation and diffraction problems. Experiments for three-cylinder cases are then designed and performed in a wave flume to determine the accuracy of this method for regular waves.

Structure-preserving properties of three differential schemes for oscillator system

Yu-yue QIN;Zi-chen DENG;Wei-peng HU

2014, 35(6):  783-790.  doi:10.1007/s10483-014-1828-6

Abstract ( 490 )   HTML   PDF (270KB) ( 239 )  

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A numerical method for the Hamiltonian system is required to preserve some structure-preserving properties. The current structure-preserving method satisfies the requirements that a symplectic method can preserve the symplectic structure of a finite dimension Hamiltonian system, and a multi-symplectic method can preserve the multi-symplectic structure of an infinite dimension Hamiltonian system. In this paper, the structure-preserving properties of three differential schemes for an oscillator system are investigated in detail. Both the theoretical results and the numerical results show that the results obtained by the standard forward Euler scheme lost all the three geometric properties of the oscillator system, i.e., periodicity, boundedness, and total energy, the symplectic scheme can preserve the first two geometric properties of the oscillator system, and the Störmer-Verlet scheme can preserve the three geometric properties of the oscillator system well. In addition, the relative errors for the Hamiltonian function of the symplectic scheme increase with the increase in the step length, suggesting that the symplectic scheme possesses good structure-preserving properties only if the step length is small enough.

Investigation of temperature effect on stress of flexspline

Qing XIANG;Zheng-nan YIN

2014, 35(6):  791-798.  doi:10.1007/s10483-014-1829-6

Abstract ( 589 )   HTML   PDF (227KB) ( 344 )  

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The effect of temperature loading on the stress of a flexspline is investigated. Based on the geometric and mechanical characteristics of the harmonic gear flexspline, a circular thin shell model is presented in this paper. The theoretical solution for the flexspline under different displacement loads and different temperature fields is derived. Meanwhile, an impact factor formula, which reflects the effect of the temperatures of the inner and outer surfaces of the flexspline on the stress of the flexspline, is presented. Finally, numerical calculations by the finite element method (FEM) are adopted to verify the corresponding conclusions.