Table of Content

01 March 2021, Volume 42 Issue 3

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Articles

Distribution of non-spherical nanoparticles in turbulent flow of ventilation chamber considering fluctuating particle number density

Ruifang SHI, Jianzhong LIN, Hailin YANG, Mingzhou YU

2021, 42(3):  317-330.  doi:10.1007/s10483-021-2707-8

Abstract ( 605 )   HTML ( 10)   PDF (2208KB) ( 147 )  

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The Reynolds-averaged general dynamic equation (RAGDE) for the nanoparticle size distribution function is derived, including the contribution to particle coagulation resulting from the fluctuating concentration. The equation together with that of a turbulent gas flow is solved numerically in the turbulent flow of a ventilation chamber with a jet on the wall based on the proposed model relating the fluctuating coagulation to the gradient of mean concentration. Some results are compared with the experimental data. The results show that the proposed model relating the fluctuating coagulation to the gradient of mean concentration is reasonable, and it is necessary to consider the contribution to coagulation resulting from the fluctuating concentration in such a flow. The changes of the particle number concentration M₀ and the geometric mean diameter d_g are more obvious in the core area of the jet, but less obvious in other areas. With the increase in the initial particle number concentration m00, the values of M₀ and the standard deviation of the particle size σ decrease, but the value of d_g increases. The decrease in the initial particle diameter leads to the reduction of M₀ and σ and the increase in d_g. With the increase in the Reynolds number, particles have few chances of collision, and hence the coagulation rate is reduced, leading to the increase in M₀ and σ and the decrease in d_g.

Nanoparticle aggregation effects on radiative heat transport of nanoliquid over a vertical cylinder with sensitivity analysis

B. MAHANTHESH, K. THRIVENI

2021, 42(3):  331-346.  doi:10.1007/s10483-021-2687-7

Abstract ( 436 )   HTML ( 2)   PDF (23868KB) ( 165 )  

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A sensitivity analysis is performed to analyze the effects of the nanoparticle (NP) aggregation and thermal radiation on heat transport of the nanoliquids (titania based on ethylene glycol) over a vertical cylinder. The optimization of heat transfer rate and friction factor is performed for NP volume fraction (1%≤φ≤ 3%), radiation parameter (1≤R_t≤3), and mixed convection parameter (1.5≤λ≤2.5) via the facecentered central composite design (CCD) and the response surface methodology (RSM). The modified Krieger and Dougherty model (MKDM) for dynamic viscosity and the Bruggeman model (BM) for thermal conductivity are utilized to simulate nanoliquids with the NP aggregation aspect. The complicated nonlinear problem is treated numerically. It is found that the temperature of nanoliquid is enhanced due to the aggregation of NPs. The friction factor is more sensitive to the volume fraction of NPs than the thermal radiation and the mixed convection parameter. Furthermore, the heat transport rate is more sensitive to the effect of radiative heat compared with the NP volume fraction and mixed convection parameter.

Numerically simulated behavior of radiative Fe₃O₄ and multi-walled carbon nanotube hybrid nanoparticle flow in presence of Lorentz force

S. A. SHEHZAD, M. SHEIKHOLESLAMI, T. AMBREEN, A. SALEEM, A. SHAFEE

2021, 42(3):  347-356.  doi:10.1007/s10483-021-2693-9

Abstract ( 384 )   HTML ( 2)   PDF (10882KB) ( 75 )  

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Free convection in hybrid nanomaterial-saturated permeable media is crucial in various engineering applications. The present study aims to investigate the free convection of an aqueous-based hybrid nanomaterial through a zone under the combined effect of the Lorentz force and radiation. The natural convection of the hybrid nanomaterial is modeled by implementing a control volume finite element method (CVFEM)-based code, whereas Darcy assumptions are used to model the porosity terms in the momentum buoyancy equation involving the average Nusselt number Nu_ave, flow streamlines, and isotherm profiles. A formula for estimating Nu_ave is proposed. The results show that the magnetic force retards the flow, and the fluid tends to attract the magnetic field source. Nu_ave is directly correlated with the Rayleigh number and radiation; however, it is indirectly dependent on the Hartmann number. Conduction is the dominant mode at larger Darcy and Hartmann numbers.

Stability analysis and modeling for the three-dimensional Darcy-Forchheimer stagnation point nanofluid flow towards a moving surface

Yuming CHU, M. I. KHAN, M. I. U. REHMAN, S. KADRY, S. QAYYUM, M. WAQAS

2021, 42(3):  357-370.  doi:10.1007/s10483-021-2700-7

Abstract ( 452 )   HTML ( 2)   PDF (1411KB) ( 133 )  

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In this research, the three-dimensional (3D) steady and incompressible laminar Homann stagnation point nanofluid flow over a porous moving surface is addressed. The disturbance in the porous medium has been characterized by the Darcy-Forchheimer relation. The slip for viscous fluid is considered. The energy equation is organized in view of radiative heat flux which plays an important role in the heat transfer rate. The governing flow expressions are first altered into first-order ordinary ones and then solved numerically by the shooting method. Dual solutions are obtained for the velocity, skin friction coefficient, temperature, and Nusselt number subject to sundry flow parameters, magnetic parameter, Darcy-Forchheimer number, thermal radiation parameter, suction parameter, and dimensionless slip parameter. In this research, the main consideration is given to the engineering interest like skin friction coefficient (velocity gradient or surface drag force) and Nusselt number (temperature gradient or heat transfer rate) and discussed numerically through tables. In conclusion, it is noticed from the stability results that the upper branch solution (UBS) is more reliable and physically stable than the lower branch solution (LBS).

Combining field-modulating electroosmotic vortex and insulating post to manipulate particles based on dielectrophoresis

Bing YAN, Bo CHEN, Fanyun LIU, Jiankang WU, Yongliang XIONG

2021, 42(3):  371-386.  doi:10.1007/s10483-021-2706-5

Abstract ( 397 )   HTML ( 3)   PDF (4092KB) ( 62 )  

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The dielectrophoretic technology has been one of the most frequently applied microfluidic technologies to manipulate particles. The way of a combination of controlled electroosmotic micro-vortices and dielectrophoresis to manipulate particles of different sizes was proposed in our previous work. However, the thickness of the modulating electrode is neglected. In practice, when the thickness of the modulating electrode increases, the channel flux increases, while the ability of the vortex to capture the particles reduces. In this study, a new method combining the field-modulating electroosmotic vortex and the insulating post is proposed to improve the manipulating capability of the field-modulated electroosmotic vortex to particles. The results indicate that there are three great advantages as the insulating post is placed on the channel wall on the same side of the modulating electrode. First, the capturing ability of the vortex to particles is greater due to the reduction of channel flux and the squeezing effect. Second, the range of regulating channel flux to achieve the optimal separation is extended. Third, the separation efficiency improves since the perfect separation can be achieved at a higher flow rate. Furthermore, the effects of the location and the size of the insulating post on particle separation are analyzed in detail. The present work could provide the reference for the application of the DEP technology.

Kinematic and mixing characteristics of vortex interaction induced by a vortex generator model: a numerical study

Ziang WANG, Bin YU, Bin ZHANG, Miaosheng HE, Hong LIU

2021, 42(3):  387-404.  doi:10.1007/s10483-021-2711-5

Abstract ( 404 )   HTML ( 2)   PDF (16436KB) ( 129 )  

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The underlying effect of vortex interaction characterized by the merging and non-merging on mixing enhancement is of fundamental significance to understand the flow dynamics of strut injectors in scramjets. Starting from a simplified configuration of a vortex generator, this study focuses on the influence of geometric parameters on vortex structures and fluid mixing through compressible Navier-Stokes (NS) simulations. By adjusting the induction of outer vortices, the inner co-rotating vortex pair exhibits two modes of interaction (merging/separation regime) reflected by closer/farther vortex centers. Defined by the zero variation rate of the inner vortex spacing, the critical state of equilibrium is determined. The critical condition is well predicted by a theoretical model based on the Biot-Savart law. Through the introduction of mixedness and mixing time, the intrinsic impact of interaction modes on fluid mixing is revealed. Compared with the vortex dynamics in the merging regime, the one in the separation regime is more effective for passive scalar mixing augmentation. With efficient material stretching characterized by the higher interface stretching factor and averaging finite-time Lyapunov exponent (FTLE), the mixing time is shortened by as much as 2.5 times in the separation regime. The implication of the present two interaction regimes in mixing enhancement physically reflected by the averaging FTLE has the potential to improve the combustion performance and shorten the combustor chamber.

New optimized flux difference schemes for improving high-order weighted compact nonlinear scheme with applications

Shichao ZHENG, Xiaogang DENG, Dongfang WANG

2021, 42(3):  405-424.  doi:10.1007/s10483-021-2712-8

Abstract ( 414 )   HTML ( 4)   PDF (5409KB) ( 123 )  

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To improve the spectral characteristics of the high-order weighted compact nonlinear scheme (WCNS), optimized flux difference schemes are proposed. The disadvantages in previous optimization routines, i.e., reducing formal orders, or extending stencil widths, are avoided in the new optimized schemes by utilizing fluxes from both cell-edges and cell-nodes. Optimizations are implemented with Fourier analysis for linear schemes and the approximate dispersion relation (ADR) for nonlinear schemes. Classical difference schemes are restored near discontinuities to suppress numerical oscillations with use of a shock sensor based on smoothness indicators. The results of several benchmark numerical tests indicate that the new optimized difference schemes outperform the classical schemes, in terms of accuracy and resolution for smooth wave and vortex, especially for long-time simulations. Using optimized schemes increases the total CPU time by less than 4%.

Torsional static and vibration analysis of functionally graded nanotube with bi-Helmholtz kernel based stress-driven nonlocal integral model

Peiliang BIAN, Hai QING

2021, 42(3):  425-440.  doi:10.1007/s10483-021-2708-9

Abstract ( 475 )   HTML ( 2)   PDF (1037KB) ( 101 )  

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A torsional static and free vibration analysis of the functionally graded nanotube (FGNT) composed of two materials varying continuously according to the power-law along the radial direction is performed using the bi-Helmholtz kernel based stress-driven nonlocal integral model. The differential governing equation and boundary conditions are deduced on the basis of Hamilton’s principle, and the constitutive relationship is expressed as an integral equation with the bi-Helmholtz kernel. Several nominal variables are introduced to simplify the differential governing equation, integral constitutive equation, and boundary conditions. Rather than transforming the constitutive equation from integral to differential forms, the Laplace transformation is used directly to solve the integro-differential equations. The explicit expression for nominal torsional rotation and torque contains four unknown constants, which can be determined with the help of two boundary conditions and two extra constraints from the integral constitutive relation. A few benchmarked examples are solved to illustrate the nonlocal influence on the static torsion of a clamped-clamped (CC) FGNT under torsional constraints and a clamped-free (CF) FGNT under concentrated and uniformly distributed torques as well as the torsional free vibration of an FGNT under different boundary conditions.

Dynamics of a multiplex neural network with delayed couplings

Xiaochen MAO, Xingyong LI, Weijie DING, Song WANG, Xiangyu ZHOU, Lei QIAO

2021, 42(3):  441-456.  doi:10.1007/s10483-021-2709-6

Abstract ( 444 )   HTML ( 2)   PDF (6336KB) ( 97 )  

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Multiplex networks have drawn much attention since they have been observed in many systems, e.g., brain, transport, and social relationships. In this paper, the nonlinear dynamics of a multiplex network with three neural groups and delayed interactions is studied. The stability and bifurcation of the network equilibrium are discussed, and interesting neural activities of the network are explored. Based on the neuron circuit, transfer function circuit, and time delay circuit, a circuit platform of the network is constructed. It is shown that delayed couplings play crucial roles in the network dynamics, e.g., the enhancement and suppression of the stability, the patterns of the synchronization between networks, and the generation of complicated attractors and multi-stability coexistence.

Static output feedback stabilization for second-order singular systems using model reduction methods

Zheng WANG, Yuhao CONG, Xiulin HU

2021, 42(3):  457-466.  doi:10.1007/s10483-021-2710-7

Abstract ( 413 )   HTML ( 3)   PDF (623KB) ( 83 )  

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In this paper, the static output feedback stabilization for large-scale unstable second-order singular systems is investigated. First, the upper bound of all unstable eigenvalues of second-order singular systems is derived. Then, by using the argument principle, a computable stability criterion is proposed to check the stability of secondorder singular systems. Furthermore, by applying model reduction methods to original systems, a static output feedback design algorithm for stabilizing second-order singular systems is presented. A simulation example is provided to illustrate the effectiveness of the design algorithm.