Abstract
Fluid flow and heat transfer processes are ubiquitous in nature and engineering. They exist in many aspects of industrial operations and daily life. Numerical simulations of these processes have been important methods for fundamental and applicable researches. This special issue focuses on the latest achievements in the two aspects. We received 63 active submissions from the United States of America, Canada, Mexico, France, Italy, Norway, Saudi Arabia, Turkey, China, Japan, Pakistan, Republic of Korea, and so forth and finally accepted 35 research articles to publish them in the special issue after peer reviews. The topics cover the researches having solid theoretical fundaments including turbulent fluid flow and heat/mass transfer and the researches having strong backgrounds of applications.
In the field of turbulent fluid flow, 10 articles have been published. The following articles make efforts on direct numerical simulation (DNS), the Reynolds averaged Navier-Stokes (RANS) model, and large eddy simulation (LES) of turbulence. The article “DNS study of the turbulent Taylor-vortex flow on a ribbed inner cylinder” by T. Tsukahara et al. shows the investigation of turbulent Taylor-vortex flows over regularly spaced square ribs mounted on a rotating inner cylinder surface. The authors find that Taylor vortices remaining over roughened cylinder surfaces can lead to less pressure drag and an enhanced backflow in the recirculation zone. The article “Turbulence modulation by small bubbles in the vertical upward channel flow” by M. Pang et al. presents the mechanisms of the liquid turbulence modulation induced by the addition of small bubbles. Intensified turbulence near the wall and slightly weakened turbulence in the channel region are discovered. In the article entitled “A modifiedk-∊model for computation of flows with large streamline curvature” by J.-L. Yin et al., the authors propose an improved RANS model for system rotation and streamline curvature effects and provide an effective way for turbulence modeling. In the article entitled “Large eddy simulation of inertial particle preferential dispersion in a turbulent flow over a backward-facing step” by B. Wang et al., LES of a turbulent flow with inertial particle dispersion over a backward-facing step is performed. The research conclusions are useful for further understanding the two-phase turbulence physics and establishing accurate engineering prediction models of particle dispersion. In the article “Comparisons of LES and RANS computations with PIV experiments on a cylindrical cavity flow” by W.-T. Su et al., RANS and LES methods are compared. The results show that LES is more suitable for predicting the complex flow characteristics inside complicated three-dimensional (3D) geometries. In the article “Experimental validation of volume of fluid method for a sluice gate flow” by A. A. Oner et al., two-dimensional (2D) open channel flow under a vertical sluice gate can be successfully analyzed by the volume of fluid (VOF) method-based modeling after the experimental validation. The following four articles focus on aerodynamics or drag reduction. “Aerodynamic performance prediction of straight-bladed vertical axis wind turbine based on CFD” by L. X. Zhang et al. demonstrates that the leading edge separation vortex and its movement on the airfoil surface have a significant impact on the aerodynamic performance because blades experience mild and deep stalls at low tip speed ratio. The article “Vortex-induced vibrations of a square cylinder with damped free-end conditions” by S. Manzoor et al. summarizes the vortex-induced vibrations of a square cylinder in a wind tunnel and suggests proper revision of the wake model used for analytical lift force predictions. In the article “The polymer effect on nonlinear processes in decaying homogeneous isotropic turbulence” by W. H. Cai et al., the authors study the behaviors of nonlinearities affected by polymer additives in decaying homogenous isotropic turbulence. They find that polymer has a negative effect on enstrophy and strain production, that is, depression of nonlinearity. In the article “Wavelet analysis on turbulent structure in drag-reducing channel flow based on direct numerical simulation” by X. Wu et al., wavelet transformation is applied to decompose velocity fluctuation time series into ten different frequency components including approximate components and detailed components. Features of turbulent multiscale structures are shown intuitively by continuous wavelet transform, verifying that turbulent structures become much more regular in drag-reducing flow.
In the field of heat/mass transfer, 9 articles have been published. The articles “Numerical analysis of flow around a moving object by an immersed boundary method with the level set method” by A. Iijima et al. and “Comparison study on linear interpolation and cubic B-spline interpolation proper orthogonal decomposition methods” by X. Wang et al. are investigations of numerical methods for fluid flow and heat transfer. The former develops a new immersed boundary method with advantages of accuracy, flexibility, and rapidness combined with the level set method. The latter concludes that the proper orthogonal decomposition method with cubic B-spline interpolation is more accurate than that with linear interpolation. In the article entitled “Numerical model on frost height of round plate fin used for outdoor heat exchanger of mobile electric heat pumps” by M.-Y. Lee, the numerical model for prediction of the frost growth of the round plate fin is established. The prediction on the frost height with time is improved by using the frost thermal conductivity reflecting the void fraction and density of ice crystal with frost growth. In the article entitled “Understanding of thermal conductance of thin gas layers” by X. Shan and M. Wang, the authors study heat conductions in a thin gas layer at micro- and nanoscales between two straight walls by atomistic modeling. They indicate that two dominating factors to the thermal conductivity reduction of thin gas layers are the temperature jump on wall surfaces and the properties changing significantly by the confined space. In the article “Modeling and numerical simulation of the grinding temperature field with nanoparticle jet of MQL” by C. H. Li et al., the heat transfer model of surface grinding temperature field with nanoparticle jet flow of MQL and the proportionality coefficient model of energy input workpiece is established. It is found that MQL grinding conditions with additive nanoparticles demonstrate great impact on the weakening of temperature effect on the grinding zone. In the article “An analytical approximation for continuous flow microwave heating of liquids” by G. Cuccurullo et al., a numerical and analytical model is developed to simulate temperature profiles in continuous laminar pipe flow during microwave heating. The simplified analytical model can lead to an easy way to predict the heat transfer through the pipe. In the article “On full-tensor permeabilities of porous media from numerical solutions of the Navier-Stokes equation” by Y. Wang et al., a new method combining Navier-Stokes equation and Darcy's law is proposed to compute full-tensor permeability of porous media instead of simplified tensor in tradition. It is found that anisotropy becomes pronounced especially when convection is dominant. The followed two articles contribute on numerical studies of mixed convection heat transfer. The article “Numerical study on the mixed convection heat transfer between a sphere particle and high pressure water in pseudocritical zone” by L. Wei et al. makes efforts on mixed convection heat transfer between supercritical water and particles in supercritical water fluidized bed reactor, which is a new but rare focused topic recently. The results show that buoyancy force has a remarkable effect on flow and heat transfer processes, and variation of specific heat and conductivity plays a main role in determination of heat transfer coefficient. Article “Numerical simulation of mixed convection in a rotating cylindrical cavity: influence of Prandtl number” by G. Urquiza et al. describes the influence of the Prandtl number on flow in critical state on a cavity containing a cooling fluid, and the heat transfer in the inferior wall increases as the Prandtl number increases and aspect ratio decreases.
Additional 16 articles with strong backgrounds of applications in industry or daily life are also published. Five articles devote efforts to petroleum industry. In the article “Numerical study on the effect of wax deposition on the restart process of a waxy crude oil pipeline” by Q. Miao, the restart process of a wax crude oil pipeline is investigated numerically by a new model for wax deposition. The temperature drop during the shutdown process and the transient inlet pressure are presented, and the effect of the wax deposition on the safety of the restart process is clarified. In the article “Analyses on heating energy saving of two hot waxy-crude oil pipelines laid parallel in one ditch” by C. Sun and B. Yu, a new technology laying two oil pipelines in one ditch employed by the petroleum companies of China is numerically presented. It is found that two hot crude oil pipelines laid parallel in one ditch can dramatically save heating energy when compared with two pipelines laid, respectively, in two separate ditches. In the article “Numerical simulation of gas-liquid-solid three-phase flow in deep wells” by J. Xie et al., a new model for gas-liquid-solid annulus flow in the deep wells is established considering the effect of the cuttings on the pressure drop. It is found that temperature and pressure are greatly affected by well depth, drilling mud density, and gas kick while the effect of the cuttings on the total pressure drop is small. In the article “Pressure change in tee branch pipe in oscillatory flow” by D. Sakamoto et al., the authors propose a simulation method to predict the pressure changes in a pneumatic branch pipe under oscillatory flow. The results contribute to the understanding of unsteady flow of branch pipes in pneumatic systems. In the article “Optimal model of operation parameters of gathering pipeline network with triple-line process” by Y. Liang et al., a mathematic model for the optimal operation of the gathering pipeline network is proposed and applied to the optimal operation analysis in North China Oilfield. Operation cost can be reduced by 2076 RMB/d, which demonstrates that this method contributes to the production cost reduction of old oilfields in their high water-cut stage. The article “Effective resistance of gas flow in microchannels” by X.-D. Shan and M.R. Wang studies fluid flow in microscale instead of macroscale for the previous five articles. They turn a complicated micromechanical problem into simple available formulae for designs and optimization of microengineering. Four articles discuss fluid flow in affiliations such as pump, tank, engine, and sprinkler. In the article “Numerical simulation of the transient process of power failure in a mixed pump” by X. Ma et al., the authors use a hydraulic-force coupling method to simulate the transient process of power failure condition. They conclude that the rotational speed decreases much faster than the flow rate in power failure accidents. In the article “Analysis on shift of nature modes of liquid sloshing in a 3D tank subjected to oblique horizontal ground motions with damping devices” by C.-H. Wu et al., the study of sloshing fluid in tanks with internal structures is extended from 2D to 3D. In the article “Numerical simulation of PAHs formation and effect of operating conditions in di-diesel engines based on a comprehensive chemical mechanism” by B.-J. Zhong and J. Xi, numerical simulations of polycyclic aromatic hydrocarbon (PAH) formation in a Chaochai 6102 bzl direct injection diesel engine are performed. PAHs first increase and then decrease with the increase in diesel crank angle. The diesel engine operating conditions have a significant effect on PAH formation. In the article “Study on the fluidic component of the complete fluidic sprinkler” by H. Li et al., the offset jet with control stream is analyzed in the simplified model. The yaw angle and the attachment angle of the offset jet flow increase with the pressure increase and vary little when the pressure is more than 0.5 MPa. Six articles are applicable researches relating artificial fish, solar energy, wood preservation, food package, champagne glasses and light. The article “Evaluation of artificial caudal fin for fish robot with two joints by using three-dimensional fluid-structure simulation” by Y. Takada et al. confirms that a good caudal fin for fish robot with two active joints is a rigid fin with a flexible material on the root by using the 3D fluid-structure interaction analysis. The article “Performance analysis and application of three different computational methods for solar heating system with seasonal water tank heat storage” by D. Sun et al. compares three different computational methods for a solar heating system with seasonal water tank heat storage. In the article “Mathematical modeling of the high temperature treatment of birch in a prototype furnace” by D. Kocaefe et al., a reliable and predictive model is developed to simulate numerically the high-temperature heat treatment process of wood preservation. In the article “Numerical simulation on the food package temperature in refrigerated display cabinet influenced by indoor environment” by Z. Chang et al., the food package temperature is investigated by numerical simulation under different conditions to study the relation between the food package temperature and ambient environment. A numerical modeling of bubble-driven flow patterns in a glass of champagne has been carried out by F. Beaumont et al. in the article “Temperature dependence of ascending bubble-driven flow patterns found in champagne glasses as determined through numerical modeling.” The velocities of the liquid phase significantly vary with the champagne temperature. In the article “Numerical study of thermal behavior in alternating current light-emitting diodes” by F.S. Hwu and H.-L. Hsieh, thermal characteristics of an alternating current light-emitting diode chip based on a 3D unsteady numerical simulation are discussed. Results show that the AC LED has a better performance under a higher frequency than under a lower frequency.