SUMMARYThis 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 firstand 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.
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-ε 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.
A characteristic-based approach is developed for thermo-flow with finite volume methodology (FVM) in which multidimensional characteristic (MC) scheme is applied for convective fluxes. Artificial compressibility (AC) is used, and as a result governing equations take the hyperbolic nature. To obtain compatibility equations and pseudo characteristics, energy equation is taken into account in the MC scheme. With MC scheme for convective fluxes, no artificial viscosity is required even at high Reynolds numbers. As benchmarks, forced convection between parallel plates and forced and mixed convection in a cavity are examined for a wide range of Reynolds, Grashof and Prandtl numbers. First-order MC and second-order averaging schemes are used for simulate them. Results show the better performance of MC scheme in force convection as well as mixed convection. Results confirm the robustness of MC scheme in terms of accuracy and convergence, and are in good agreement with the standard benchmark solutions in the literature.
Introduction:
Venous valves are a type of one-way valves which conduct blood flow toward the heart and prevent its backflow. Any malfunction of these organs may cause serious problems in the circulatory system. Numerical simulation can give us detailed information and point to point data such as velocity, wall shear stress, and von Mises stress from veins with small diameters, as obtaining such data is almost impossible using current medical devices. Having detailed information about fluid flow and valves' function can help the treatment of the related diseases. Methods: In the present work, the blood flow through a venous valve considering the flexibility of the vein wall and valve leaflets is investigated numerically. The governing equations of fluid flow and solid domain are discretized and solved by the Galerkin finite element method. Results: The obtained results showed that the blood velocity increases from inlet to the leaflets and then decreases passing behind the valve. A pair of vortices and the trapped region was observed just behind the valves. These regions have low shear stresses and are capable of sediment formation. Conclusion: The von Mises stress which is a criterion for the breakdown of solid materials was obtained. It was also observed that a maximum value occurred at the bottom of the leaflets.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.