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The application of nanofluids has exploded in recent decades to improve the local number, mean Nusselt number, and rate of heat transfer. However, boundary layer equations of nanofluid across a flat plate with radiation have not been studied, and therefore this paper studies them mathematically for the first time. For water-based copper and aluminum oxide nanofluids, a similarity solution is presented in this study, and the subsequent system of the ordinary differential equation (ODE) is numerically solved by the Runge–Kutta method in MATLAB. Two different hydraulic boundary conditions are used in the simulations. In the first, the flow across a moving plate and the direction of the flow are analyzed, while in the second, the flow over a nonlinearly moving plate in a still fluid is investigated. The nanoparticle's boundary layer thickness is found less than the thermal and hydraulics boundary layers. The local Nusselt number and friction factor of both the nanofluids are calculated and compared with the base fluid. The results demonstrate that the friction coefficient is high and the Nusselt number is low for nanoparticles with a high volume fraction. It also revealed that the friction factor for water–aluminum oxide is 16% greater than that for the water–CuO whereas the local Nusselt number for water–aluminum oxide is only 5% more than that for the water–CuO. [ABSTRACT FROM AUTHOR]

AbstractIn the present investigation, a numerical investigation of the flow and heat transfer characteristics inside an L-shaped enclosure with a flexible fin and an elastic wall has been carried out using the finite element method. The Fluid-Structure Interaction model is used to capture the interaction between the fluid and the solid structure. The free end of the flexible fin is exposed to sinusoidal vertical force and the upper wall of the enclosure is considered to be elastic and a sinusoidal force is applied on this elastic wall. The obtained results showed that the fluid flow through the enclosure is entirely influenced by the periodic oscillation of the flexible fin and elastic wall. Besides, the Nusselt number over the horizontal and vertical hot walls of the L-shaped enclosure is strongly affected by the amplitude and frequency of the applied sinusoidal forces on the flexible fin and elastic wall. The heat transfer over the vertical hot wall is enhanced considerably with an increase in the amplitude and frequency of the applied sinusoidal forces. Moreover, the Nusselt number over the hot vertical wall is increased with the decrease of the elastic modulus value of the elastic wall. The results also show that the combination of the flexible fin and elastic wall has contributed to the extra enhancement of the Nusselt number over the hot vertical wall of the L-shaped enclosure. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The numerical solution of compressible flows has become more prevalent than that of incompressible flows. With the help of the artificial compressibility approach, incompressible flows can be solved numerically using the same methods as compressible ones. The artificial compressibility scheme is thus widely used to numerically solve incompressible Navier-Stokes equations. Any numerical method highly depends on its accuracy and speed of convergence. Although the artificial compressibility approach is utilized in several numerical simulations, the effect of the compressibility factor on the accuracy of results and convergence speed has not been investigated for nanofluid flows in previous studies. Therefore, this paper assesses the effect of this factor on the convergence speed and accuracy of results for various types of thermo-flow. To improve the stability and convergence speed of time discretizations, the fifth-order Runge-Kutta method is applied. A computer program has been written in FORTRAN to solve the discretized equations in different Reynolds and Grash of numbers for various grids. The results demonstrate that the artificial compressibility factor has a noticeable effect on the accuracy and convergence rate of the simulation. The optimum artificial compressibility is found to be between 1 and 5. These findings can be utilized to enhance the performance of commercial numerical simulation tools, including ANSYS and COMSOL. [ABSTRACT FROM AUTHOR]

In this paper, flow characteristics, heat transfer and entropy generation in a rotating curved duct are studied numerically. The continuity, Navier-Stokes and energy equations are solved using control volume method. The effects of Dean number, non-dimensional wall heat flux, and force ratio (the ratio of Coriolis tocentrifugal forces) on the entropy generation due to friction and heat transfer irreversibility and also overall entropy generation are presented. Optimal thermaloperating conditions (based on dimensionless parameters) are determined fromthe viewpoint of thermodynamics second law. The comparison of numerical results at different force ratios indicates that for any fixed Dean number or non-dimensional heat flux, the minimal frictional entropy generation occurs when theCoriolis and centrifugal forces have the same value but in the opposite direction.For a specific non-dimensional heat flux, there is a force ratio with maximumheat transfer irreversibility which depends on Dean number. Based on optimal analysis, the optimal force ratio with minimal total entropy generation depends on heat flux and Dean number. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Introduction: Atherosclerosis is a focal disease that susceptibly forms near bifurcations, anastomotic joints, side branches, and curved vessels along the arterial tree. In this study, pulsatile blood flow in a bifurcation model with a non-planar branch is investigated. Methods: Wall shear stress (WSS) distributions along generating lines on vessels for different bifurcation angles are calculated during the pulse cycle. Results: The WSS at the outer side of the bifurcation plane vanishes especially for higher bifurcation angles but by increasing the bifurcation angle low WSS region squeezes. At the systolic phase there is a high possibility of formation of a separation region at the outer side of bifurcation plane for all the cases. WSS peaks exist on the inner side of bifurcation plane near the entry section of daughter vessels and these peaks drop as bifurcation angle is increased. Conclusion: It was found that non-planarity of the daughter vessel lowers the minimum WSS at the outer side of the bifurcation and increases the maximum WSS at the inner side. So it seems that the formation of atherosclerotic plaques at bifurcation region in direction of non-planar daughter vessel is more risky. [ABSTRACT FROM AUTHOR]

Introduction: Arterial bifurcations are susceptible locations for formation of atherosclerotic plaques. In the present study, steady blood flow is investigated in a bifurcation model with a non-planar branch., Methods: The influence of different bifurcation angles and non-planar branch is demonstrated on wall shear stress (WSS) distribution using three-dimensional Navier-Stokes equations., Results: The WSS values are low in two locations at the top and bottom walls of the mother vessels just before the bifurcation, especially for higher bifurcation angles. These regions approach the apex of bifurcation with decreasing the bifurcation angle. The WSS magnitudes approach near to zero at the outer side of bifurcation plane and these locations are separation-prone. By increasing the bifurcation angle, the minimum WSS decreases at the outer side of bifurcation plane but low WSS region squeezes. WSS peaks exist on the inner side of bifurcation plane near the entry section of daughter vessels and these initial peaks drop as bifurcation angle is increased., Conclusion: It is concluded that the non-planarity of the daughter vessel lowers the minimum WSS at the outer side of bifurcation and increases the maximum WSS at the inner side. So it seems that the formation of atherosclerotic plaques at bifurcation region in direction of non-planar daughter vessel is more risky.

Introduction: In this research the behavior of coronary arteries has been studied with symmetric and asymmetric consecutive stenosis, and grafted vessels., Methods: The incompressible Navier-Stokes and energy equations were discretized with second-order upwind method. Assumptions such as Newtonian fluid, wall rigidity and steady-flow were used., Results: All the calculations showed the same results with Newtonians and non- Newtonian fluids. It was found that the possibility of stenosis be reduced by increasing the graft angle. However, there exists further stenosis possibility. Among the three graft angles 20, 30 ˚ and 40, the 30 ˚ was found to be the reliable ones., Conclusion: Based on these findings, it can be deduced that there would be a high risk of further atherosclerosis when the first stenose has the maximum percentage.