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In this research, a combination of passive and active heat transfer enhancements are used synergistically to assist in the increase of absorbed heat from a channel by roughened and fluctuating walls. To this end, the upper wall is artificially roughened and a fluctuating segment is added to the lower wall. Flow regime is considered to be laminar and Reynolds number is 1000 at the entrance of the channel. Combinations of various roughness geometries and fluctuations are studied. It was found that due the increase of the fluid kinetic energy and its interaction with roughened surface and elastic segment, heat transfer rate is amplified. To investigate the overall efficiency of the system, Nusselt number and friction factor are calculated and a maximum value of 37.5% increase in average Nusselt number of the midsection where elastic wall is placed has been reached by flexible plate displacement. A maximum Nusselt number increase of 167% has been observed when the elastic plate reaches its peak value.

In this study, the flagellar motility of a swimmer microorganism as a model of a human sperm cell, inside a two-dimensional channel as a model of the female reproductive tract containing a viscous fluid, is numerically investigated. The Navier–Stokes equations governing the fluid are coupled with the equations governing the models flagellum via applying a fluid–solid interaction approach and then solved using the finite element method. To stimulate the flagellum to move, a prescribed sinusoidal waveform is applied to it. The strain induced by this waveform along the flagellum initiates a continuous interaction between the flagellum and the fluid. The simulations are validated using data available in the literature. A very good agreement is seen between them. The results show that by decreasing the Young modulus of the flagellum as well as increasing the fluid viscosity, the swimming velocity of the model significantly decreases. It is found that for lower Young modulus of the flagellum, the effect of the fluid viscosity on the flagellar deformation is stronger. It is also found that for higher amplitude of the waveform applied to stimulate the flagellum, both the swimming velocity of the model and the average work rate are greater. Moreover, it is found that in a channel with a smaller height, the model swims at a higher speed and with a higher average work rate.

Natural gas must be preheated to prevent phase change and gas hydrate in pressure reduction stations. This paper aims to investigate the effect of the fins of gas tubes and their configuration, arrangement, and shape on the heat transfer and thermal efficiency of gas. To conduct a parametric study, two tube cases with fins and without fins, and in the finned case for the fin’s configuration, two longitudinal and circular arrangements, and the formation of the fins, two solid and interrupted forms were analyzed. Also, three types of cross-sections, including rectangular, convergent parabolic, and divergent parabolic, for the shape of the fins have been studied. For this simulation, the three-dimensional, incompressible, and steady flow was considered, and for analysis and discretization of convective heat equations, the characteristic-based method was applied. FORTRAN software was also used to implement and solve the equations. The results show that in solid and interrupted fins and increasing the number of fins in parallel, the dimensionless heat transfer coefficient increases. Also, the dimensional heat transfer coefficient decreases with increasing the ratio of fin height to the tube’s diameter. Also, the most significant heat transfer improvement was related to the divergent parabolic cross-section.

In the present work, the laminar flow through a circular cylinder with two crossed splitter plates is analyzed. The characteristic-based method has been used along with the unstructured grid. The current research has been done to detect the proper conditions according to the geometrical parameters in which the optimal heat transfer is taking place. Geometric control parameters are the angle of splitter plates (\theta) and the ratio of length of the splitter plate to cylinder radius (n=L/D). It was found that the use of a two-branched splitter plate is not wise in Reynolds number less than 100 due to its insignificant effect in flow properties. In angle 30° between two plates, the least drag force is witnessed with respect to other angles. Application of double branched splitter with angles more than 60° is not recommended, which will increase the total drag significantly. Since the splitter plate increases, the overall heat transfer from the cylinder and splitter set is enhanced. Minimum drag over the cylinder, and maximum convection drop from it is taken place when the dimension length is 0.75. Between dimensionless lengths 1.25 and 1.5, the Nusselt number oscillates with least amplitude and such behavior is also observed when two splitters are 60°apart.

In the internal combustion engines geometry of the injector orifice has significant effect on the improving of the fuel spray characteristics. In the present paper, effect of a conical annulus injector with three different aspect ratios and three different divergence angles of the annulus orifice on the hydrodynamic behavior of a fuel spray have been investigated numerically. The conical annulus injector aspect ratio is the ratio of the height of the annulus cone to the diameter of its circular base. The geometry of the annulus conical injectors inspires this idea that this type of injectors could inject possible large amount of liquid fuel into a combustion chamber symmetrically and homogeneously. The CFD software AVL Fire has been employed for numerical simulation of diesel fuel spray evolution. Numerical results show that the annulus conical injectors inject liquid fuel with an approximately homogenous distribution of droplets in the combustion chamber in comparison with the conventional injectors. In this kind of injector, fuel has been uniformly distributed in the cylinder. Numerical results also show that the annulus injectors significantly increase the cone angle of the liquid fuel spray and decrease its penetration length.

Introduction: The middle cerebral artery (MCA) is one of the three major paired arteries that supply the blood to the cerebrum. In the present study, the three-dimensional (3D) blood flow in the left MCA was numerically simulated by using the medical imaging. Methods: The arterial geometry was obtained by applying the CT angiography of the MCA of a 75-year-old man. The blood flow was assumed to be laminar and unsteady. Numerical simulations were done by commercial software package COMSOL Multiphysics 5.2. In this software, the Galerkin’s finite element method was applied to solve the governing equations. Results: It was found that the results obtained for the Newtonian and non-Newtonian models of blood do not differ from each other significantly. Thus, the Newtonian model for blood flow in the MCA is acceptable. Also, the most susceptible region of the MCA for Atherosclerosis was detected. Conclusion: It can be concluded that the application of the Newtonian model for the blood flowing in the MCA is acceptable. Also, atherosclerosis has the potential to occur at the middle of a branch of the MCA which has the highest geometrical curvature.

The drag suppression for a high-amplitude oscillating cylinder is simulated using various configurations of detached-splitter plates. Governing parameters are the length of splitters (L), the cylinder–splitter gap (G), the amplitude (A), and the frequency of oscillation (f0). The control-volume technique along with the ACMI (arbitrary coupled mesh interface) boundary treatment and dynamic mesh technique are used to capture the high-amplitude boundary movement. It is found that in comparison to the dynamic mesh technique, the ACMI boundary condition is more efficient for highly deforming boundaries between two adjacent domains. Furthermore, it is found that the case with double upstream splitter has the most drag reduction. The lock-on and unlocked regions for a cylinder with diameter of D are identified for dimensionless amplitudes of A / D = 0.25 and A / D = 0.5 , and the minimum values of drag coefficient for various magnitudes of dimensionless gap ( G / D ) are found. Also, the locked and unlocked configurations play an important role in the drag reduction mechanism. It is concluded that the maximum drop in the drag force occurs for the lock-on condition at dimensionless oscillation frequency of F=1.1. It is concluded that the gap size and the plate length are the least and the most effective quantities, respectively.

In this paper, incompressible thermo-flow is simulated for a channel and with and without baffles. A baffle is connected to the channel from different angles. The effect of perforated inclined baffles on the flow pattern and heat transfer in a channel investigated. The computations are based on the finite element method, Galerkin scheme, and Newton–Raphson iterative method have been implemented. The flow regime was assumed to be laminar. Results show that the use of perforated baffles leads to an increase in the Nusselt number and minimized friction factor in comparison to the plain ones. The numerical results are compared with the available solutions in the literature. The defined efficiency of the baffle is obtained for various baffle types, baffle’s angle, Reynolds number, and baffle’s ratios. The optimum angle of the baffle inclinations was obtained. It was found that perforated baffles demonstrate show superior performance when compared with plain counterparts. Also, there is local heat transfer enhancement at the downstream of the stepped baffle caused by the impinging effect of flow, which is even more significant when baffle height becomes higher or the Reynolds number elevates. Obtained results show that a 135° perforated baffle is a better choice as it enhances the heat transfer with a minimal friction factor.

Two common abnormalities in ureters include primary refluxing megaureter (PRM) and primary obstructed megaureter (POM). The aim of this study was to represent the numerical simulation of the urine flow at the end of the ureter with vesicoureteral reflux (VUR) and POM during peristalsis. Methodologically, the peristalsis in the ureter wall was created using Gaussian distribution. Fluid-structure interaction (FSI) was applied to simulate urine-elastic wall interactions; and governing equations were solved using the arbitrary Lagrangian-Eulerian method. Theories such as wall elasticity, Newtonian fluid, and incompressible Navier-Stokes equations were used. Velocity fields, viscous stresses and volumetric outflow rate profiles were obtained through the simulation of the ureter with VUR and POM during peristalsis. In addition, the effect of urine viscosity on flow rate was investigated. When the bladder pressure increased, VUR occurred because of the ureterovesical junction (UVJ) dysfunction, leading to high stresses on the wall. In the POM, the outflow rate was ultimately zero, and stresses on the wall were severe in the obstructed section. Comparing the results demonstrated that the peristalsis leads to even further dilation of the prestenosis portion. It was also observed that the reflux occurs in the ureter with VUR when the bladder pressure is high. Additionally, the urine velocity during the peristalsis was higher than the non-peristaltic ureter.

A novel multidimensional characteristics approach for inflow and outflow boundaries of compressible twodimensional flows is presented. The modified Riemann variables have been extracted from the Euler equations by considering the directions of waves reaching the inflow and outflow boundaries. By applying this model in a shortened computational domain, the boundaries can be located close to the nonlinear zone. The results of reduced and extended domains are in good agreement with each other. Using this model yields in a reduction of computational domain while keeping the solution accuracy and lowering the computation time.

This paper presents a Splitter Plate Pin-Fin Heat Sink (SPPFHS) as a new kind of heat sink to enhance hydro-thermal performance of heat sinks. To reach this purpose, a thin plate known as a splitter is located behind the pin-fin. According to the numerical results, placing the splitter behind the pin-fin, reduces the thermal resistance and pressure drop on the heat sink. Splitter streamlines the flow around the cylinder and decreases the pressure drop around the pin-fins. Besides the pressure drop, increase of heat-transfer area dominates the heat transfer coefficient reduction and results to thermal resistance decrement. Furthermore, for considering the both thermal resistance and pressure drop effects; non-dimensional parameter of profit factor ( J ) is computed. Comparison between present SPPFHS and Plate Pin Fin Heat Sink (PPFHS) confirms the ability of splitter in modification of hydro-thermal behavior of heat sinks by simultaneous reducing the pressure drop and thermal resistance.

Introduction: Employing of gaseous plugs inside a vein for preventing of blood flow to the damaged or cancerous tissues has been known as a gas embolism in the medicine. In this research, a numerical investigation has been carried out on the delivery of the liquid drug DDFP, encapsulated in the microlipid-coated spheres (MLCSs), to target the human vein for construction of the gaseous plug inside the veins. Methods: The encapsulated liquid drug DDFP were delivered to the vein by injection of an emulsion. Releasing of the liquid drug DDFP results in an explosive growth of a gaseous plug inside the vein. The targeted vein was served as a rigid cylinder with a compliant coating. The boundary integral equation method has been employed for the numerical simulation of the hydrodynamic behavior of the gaseous plug inside the vein. Results: Numerical results showed that in the case of a rigid cylinder vein with an internal compliant coating, the maximum volume of the gaseous plug was smaller than the case of just a rigid cylinder vein. Furthermore, its elapsed time from the instant of bubble generation to the instant when the bubble reaches its maximum volume was shorter. Numerical results also showed that the compliant coating on the internal wall of the rigid cylindrical vein had a tendency of reducing the impact of the explosive growth of the gaseous plug. Conclusion: This numerical research showed that the compliant coating on the internal wall of the rigid cylindrical vein had the tendency of reducing the impact of the impulsive growth of the gaseous plug. Therefore, in the case of having severed arteriosclerosis, treatment of the cancerous or damaged tissues by use of the gaseous embolism must be done very carefully in order to prevent the hazardous effects of the gaseous plug’s impulsive growth.

SUMMARY In the current study, numerical investigation of incompressible turbulent flow is presented. By the artificial compressibility method, momentum and continuity equations are coupled. Considering Reynolds averaged Navier–Stokes equations, the Spalart–Allmaras turbulence model, which has accurate results in two-dimensional problems, is used to calculate Reynolds stresses. For convective fluxes a Roe-like scheme is proposed for the steady Reynolds averaged Navier–Stokes equations. Also, Jameson averaging method was implemented. In comparison, the proposed characteristics-based upwind incompressible turbulent Roe-like scheme, demonstrated very accurate results, high stability, and fast convergence. The fifth-order Runge–Kutta scheme is used for time discretization. The local time stepping and implicit residual smoothing were applied as the convergence acceleration techniques. Suitable boundary conditions have been implemented considering flow behavior. The problem has been studied at high Reynolds numbers for cross flow around the horizontal circular cylinder and NACA0012 hydrofoil. Results were compared with those of others and a good agreement has been observed. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, Thermal Finite-Volume Lattice Boltzmann Method is developed. To demonstrate the temperature field, the Double Distribution Function (DDF) of thermal lattice Boltzmann equation is used. The upwind biasing factors based on pressure and temperature are defined and applied as flux corrector in the thermo-hydrodynamic lattice Boltzmann equations. A consistent open and solid boundary treatment of flow is also addressed. The unknown energy distribution at the boundary cells are decomposed into its equilibrium and non-equilibrium parts. Then the non-equilibrium part is approximated with extrapolation of the non-equilibrium part of the populations at the neighboring nodes. This treatment enlarges the domain stability and led up to faster convergence. Two test cases namely, thermo-hydrodynamic in a backward-facing step and around a circular cylinder inserted within a backward-facing step are carried out. The results are compared with the available solutions in the technical literature.

In this article, a novel approach for flux treatment is presented in conjunction with cell-centred Finite-Volume Lattice Boltzmann Method (FVLBM). The distribution functions are determined by using a pressure-based flux weighting factor on a D2Q9 lattice. A consistent open and solid boundary treatment is also addressed, which resulted in a wider domain of stability and faster convergence. For time discretisation, a fifth-order Runge-Kutta algorithm was applied. An in-house FORTRAN code has been written by the authors which uses the time-marching along with FVLBM. Two test cases, namely, flow over a backward-facing step and around a circular cylinder are carried out. The results are compared with the available solutions in which favourable agreement was observed.

This paper presents a novel multidimensional characteristic-based (MCB) upwind method for the solution of incompressible Navier–Stokes equations. As opposed to the conventional characteristic-based (CB) schemes, it is genuinely multidimensional in that the local characteristic paths, along which information is propagated, are used. For the first time, the multidimensional characteristic structure of incompressible flows modified by artificial compressibility is extracted and used to construct an inherent multidimensional upwind scheme. The new proposed MCB scheme in conjunction with the finite-volume discretization is employed to model the convective fluxes. Using this formulation, the steady two-dimensional incompressible flow in a lid-driven cavity is solved for a wide range of Reynolds numbers. It was found that the new proposed scheme presents more accurate results than the conventional CB scheme in both their first- and second-order counterparts in the case of cavity flow. Also, results obtained with second-order MCB scheme in some cases are more accurate than the central scheme that in turn provides exact second-order discretization in this grid. With this inherent upwinding technique for evaluating convective fluxes at cell interfaces, no artificial viscosity is required even at high Reynolds numbers. Another remarkable advantage of MCB scheme lies in its faster convergence rate with respect to the CB scheme that is found to exhibit substantial delays in convergence reported in the literature. The results obtained using new proposed scheme are in good agreement with the standard benchmark solutions in the literature. Copyright © 2007 John Wiley & Sons, Ltd.

Introduction: Among cardiovascular diseases, arterials stenosis is recognized more commonly than the others. Hemodynamic characteristics of blood play a key role in the incidence of stenosis. This paper numerically investigates the pulsatile blood flow in a coronary bifurcation with a non-planar branch. To create a more realistic analysis, the wall is assumed to be compliant. Furthermore, the flow is considered to be threedimensional, incompressible, and laminar. Methods: The effects of non-Newtonian blood, compliant walls and different angles of bifurcation on hemodynamic characteristics of flow were evaluated. Shear thinning of blood was simulated with the Carreau-Yasuda model. The current research was mainly focused on the flow characteristics in bifurcations since atherosclerosis occurs mostly in bifurcations. Moreover, as the areas with low shear stresses are prone to stenosis, these areas were identified. Results: Our findings indicated that the compliant model of the wall, bifurcation’s angle, and other physical properties of flow have an impact on hemodynamics of blood flow. Lower wall shear stress was observed in the compliant wall than that in the rigid wall. The outer wall of bifurcation in all models had lower wall shear stress. In bifurcations with larger angles, wall shear stress was higher in outer walls, and lower in inner walls. Conclusion: The non-Newtonian blood vessels and different angles of bifurcation on hemodynamic characteristics of flow evaluation confirmed a lower wall shear stress in the compliant wall than that in the rigid wall, while the wall shear stress was higher in outer walls but lower in inner walls in the bifurcation regions with larger angles.

The enhancement of heat transfer by the turbulator ribs in cooling channels causes increases of pressure drop. To achieve high thermal performance, a variety of techniques are employed. This study numerically investigates the heat transfer, fluid flow and thermal performance factor in the rib-roughened straight rectangular channel. The ribs have a circular shape and are mounted on the two opposite walls in a staggered arrangement. Four different rib attack angles of 90°, 60°, 45° and 30° to the main flow direction are treated. The results are obtained at entrance Reynolds number of range 25 000–50 000. Air is considered as convective fluid in steady state distribution. The three-dimensional flow is simulated with a two-layer k -e turbulence model. The governing equations are solved by a control-volume based procedure using second-order upwind scheme. The computational results are compared with the experimental data under the same conditions. It is found that regarding heat transfer enhancement, circular ribs are in preference to block ones. In addition, the angled ribs could enhance the heat transfer significantly when compared to the ribs in 90° due to the generation of secondary flows. Concerning thermal performance factor, the optimum rib angle is also proposed for different Reynolds numbers.