Subrat Das

Transient fluid–structure coupling for simulation of a trileaflet heart valve using weak coupling

In this article, a three-dimensional transient numerical approach coupled with fluid–structure interaction for the modeling of an aortic trileaflet heart valve at the initial opening stage is presented. An arbitrary Lagrangian–Eulerian kinematical description together with an appropriate fluid grid was used for the coupling strategy with the structural domain. The fluid dynamics and the structure aspects of the problem were analyzed for various Reynolds numbers and times. The fluid flow predictions indicated that at the initial leaflet opening stage a circulation zone was formed immediately downstream of the leaflet tip and propagated outward as time increased. Moreover, the maximum wall shear stress in the vertical direction of the leaflet was found to be located near the bottom of the leaflet, and its value decreased sharply toward the tip. In the horizontal cross section of the leaflet, the maximum wall shear stresses were found to be located near the sides of the leaflet.

Effect of Darcy, fluid rayleigh and heat generation parameters on natural convection in a porous square enclosure: A Brinkman-extended Darcy model

Abstract A Pressure-velocity solution for natural convection for fluid saturated heat generating porous medium in a square enclosure is analysed by finite element method. The numerical solutions obtained for wide range of fluid Rayleigh number, Raf, Darcy number, Da, and heat generating number, Qd. The justification for taking these non-dimensional parameters independently is to establish the effect of individual parameters on flow patterns. It has been observed that peak temperature occurs at the top central part and weaker velocity prevails near the vertical walls of the enclosure due to the heat generation parameter alone. On comparison, the modified Rayleigh number used by the earlier investigators[4,6], can not explain explicitly the effect of heat generation parameter on natural convection within an enclosure having differentially heated vertical walls. At higher Darcy number, the peak temperature and peak velocity are comparatively more, resulting in better enhancement of heat transfer rate.

Numerical analysis and experimental validation of high pressure gas quenching

Aided by the computational fluid dynamics package CFX-4 a transient flow model has been used to simulate the process of high pressure gas quenching of a large H13 die. The predicted temperature distributions, obtained under steady and transient flow conditions, together with experimental data have been compared, and a good agreement was obtained. This suggests that a steady state simulation can be effectively used in this type of study to achieve accurate simulated data with reduced computational time. This series of studies is seen as the precursor to the development of an overall simulation procedure for simultaneous distortion and heat transfer characterisation of the die leading to optimum heat treatment control.

A non-Darcian numerical modeling in domed enclosures filled with heat-generating porous media

ABSTRACT Numerical study of the natural-convection flow and heat transfer in a dome-shaped, heat-generating, porous enclosure is considered. The general conic equation for the top dome is used to consider various conical top sections such as circular, elliptical, parabolic, and hyperbolic. The individual effect of fluid Rayleigh, Darcy, and heat-generating parameters on flow patterns and heat transfer rates are analyzed and presented. The predicted results show that the heat-generating parameter has the most significant contribution toward the growth of bicellular core flow. Moreover, there is significant change in temperature distribution in comparison to rectangular enclosures, due to the existence of the domed-shape top adiabatic cover. The results also show that, regardless of Darcy and Rayleigh values, a flat adiabatic top cover tends to yield the highest value of Nusselt number, followed by circular, elliptical, parabolic, and hyperbolic top covers, respectively.

Natural convection inside dome shaped enclosures

In the present paper the analysis of heat transfer and free convective motion have been carried out numerically for dome shaped enclosures. The solution method is based on the finite element technique with the frontal solver and is used to examine the flow parameters and the heat transfer characteristics inside dome shaped enclosures of various offsets. In formulating the solution a general conic equation is considered to represent the dome of circular, elliptical, parabolic and hyperbolic shapes. The numerical results indicate that the circular and elliptical shapes of dome give higher heat transfer rate and offset of the dome effects convective heat transfer quite significantly. However, beyond 0.3 top dome offset, the change in overall heat transfer rate is not significant. In addition, the convective phenomenon influenced by a dome shaped cover results in establishing a secondary core region even at a moderate Rayleigh number when compared with an equivalent rectangular enclosure. A good comparison between the present numerical predictions and the previous published data is achieved.

Analysis of droplet mixing and splitting operations by a low actuation voltage electrowetting-on-dielectric device

This paper presents an electrowetting-on-dielectric (EWOD)-based droplet mixing and splitting device. In the proposed method, the droplet is sandwiched between the bottom and top substrate plates of the EWOD device. A dielectric layer of Parylene C and a thin coating of a hydrophobic Teflon layer are used to create the EWOD device. The device actuates the droplets by applying an electric potential and thus increases the wettability of the droplet on the EWOD surface. The Finite Element Method (FEM) based Coventorware software is used to accomplish the simulations. The simulated result shows that a significant change in contact angle (120° to 80°) of the droplet is occurred during the operations of both mixing and splitting. The EWOD device with Parylene C layer of 2 μm thickness and Teflon layer of 50 nm thickness started both droplet mixing and splitting operations at a low actuation voltage of 30 V.

Convection in Fluid Overlying Porous Layer: An Application to Hall–Héroult Cell

Finite-element method is used to predict the buoyancy-driven convection in a horizontal layer of fluid (aluminum melt) overlying a porous layer (cathode) saturated with the same fluid. This work aims to compare the Hall–Heroult process in electrolytic cell, where a layer of molten aluminum is reduced over the porous cathode surface. In this study, the physical system of the aluminum melt (fluid) and cathode (porous) together is considered as a composite system of fluid overlying porous layer. The main objective of this study to analyse the velocity components in thin fluid layer and its impact on a porous cathode surface if there is any. In addition, an externally imposed time-independent uniform magnetic field is used to analyse its influence on natural convective forces. The physical system of fluid overlying porous layer is analysed at different Hartmann, Darcy, and fluid-Rayleigh numbers for a fixed Prandtl number (Pr = 0.014). The predicted data show that the convective forces, caused by buoyancy-driven flow, are significant. It is shown that the velocity peaks moves toward the solid wall because of the presence of a magnetic field creating a stronger boundary-layer growth over the permeable cathode surface. The predicted results are plotted in terms of average Nusselt number and Darcy number to indicate the influence of pores and permeability on overall convective heat-transfer characteristics.

Pressure-velocity formulation to study the effect of protuberance on thermal convection by finite element method

The analyses of heat transfer and free convective motion have been carried out numerically for a semi-cylindrically shaped protuberance in a square enclosure. The solution method is based on the finite element technique with the frontal solver. The numerical results are for a Prandtl number 0.71 and for Rayleigh number up to 10 5 . The change in the direction of the returning fluid near the cold wall, due to the presence of protuberance at the bottom, results higher convective current. Increase in protuberance results the maximum velocities in the domain and creates dead zones near the bottom corners of the enclosures

Analysis of Flow Field in a T-Bifurcation Model

The flow and wall shear stress in a 90° T-bifurcation model is analyzed numerically. The nonlinear Navier-Stokes equations for incompressible Newtonian fluid flow are approximated using finite volume method approximation. The wall shear stress is calculated from the velocity field. The investigation shows viscous flow phenomena such as flow separation and stagnation and the distribution of high and low wall shear stress during flow through the tube. Furthermore, the effect of a sharp corner at the bifurcation edge on the wall shear stress is analyzed.