unsteady flow

The erratic natural convection and mass transit flow of a viscous incompressible as well as electrically conducting fluid over an impetuously started immeasurable vertical flat plate immersed in the porous medium may occur in many engineering applications. By virtue of these various applications, in the present article, we have considered Soret and Dufour effects on erratic Magnetohydrodynamic natural convection fluid flow. With aid of similarity transformation, the partial differential equations of the flow, which are non - linear, are converted into a group of ordinary differential equations. Later on, those equations are linearized and solved by making use of numerical technique called implicit finite difference method. The derived results of velocity, temperature and concentration profiles are demonstrated through graphs for various values of the physical parameters, which influences the fluid flow. The temperature distribution of the fluid increases with increase in Dufour number, whereas the concentration profiles decreases with the increase in Dufour number or decrease in Soret number.Lastly, the impact of various parameters on local-skin friction, local-Nusselt number, and local-Sherwood number are also presented in the tabular form.

This study presents an innovative and simple way to increase the rate of heat transfer in a spiral plate heat exchanger model. Several circular cross-section rods, as continuous vortex generators, have been inserted within the spiral plate heat exchanger in the cross-stream plane. The vortex generators are located at various azimuth angles of α=30◦, 60◦, 90◦, and 120◦ with non-dimensional diameters of d/H=0.3, 0.4, and 0.5. Computations have been carried out numerically by means of the finite volume approach under different Dean numbers (De) ranging from 500 to 1500 in the laminar regime. The flow physics within the advanced spiral heat exchanger model has been discussed using several velocity and temperature contours. It was found that by inserting the continuous vortex generators in the cross-stream plane of a spiral plate heat exchanger, the unsteady flow develops within the channel in which the rate of unsteadiness is proportional to d/H and De directly and to azimuth angle inversely. The maximum heat transfer enhancement with respect to the conventional spiral plate heat exchanger (without continuous vortex generators) is found to be 341% for α=30◦, d/H=0.5, and De=1500. Additionally, values of pressure drop penalty and thermal-hydraulic performance have been determined accordingly.

The objective of current paper is 3D simulation of turbulent, developing flow and unsteady within a circular duct in presence of the body force vector persuaded by Dielectric barrier discharge (DBD) plasma actuator inside the surface of geometry for the first time. This article aims at investigating of applying plasma actuator to control separation with special arrangement of electrodes. For this reason, the plasma actuator is modeled in OpenFOAM software and the results are validated.Subesequently, to examine the effect of the presence of the plasma actuator a numerical study is carried out on a 3D flow. The physics of the problem is determined by three phenomena of increasing the flow cross-sectional, developing flow and simultaneous flow in both radial and tangential directions, especially the pressure gradients. As a result of the geometry of the problem, the actuators are arranged differently and the electrodes are arranged in radial direction. The results indicate that plasma actuator delay the separation point.

This paper deals with numerical study of semi-finite incompressible flow of air over two blocks with different heights in the presence of a condensing-source, dispensing- contaminant in the flow, in both steady and unsteady states. The numerical solution of governing PDE equations are constructed by a finite-volume method applied on structured grid arrangement. The effects of air flow velocity, contaminant source length and position, and the blocks height ratio on the concentration distribution, the mass transfer level and the time of transportation are studied. The results indicate that by increasing the inflow Reynolds number, the amount of contamination reaching the blocks and also the amount remaining between them decrease, while the mass transfer rate increases. It is shown that the closer the contaminant source to the blocks, the higher the mean concentration accumulating between the two blocks. It is also found that increasing the blocks'' height ratio makes an ascending trend to the time for the arrival of contaminant to the blocks'' walls, though the slopes of time-lines are different for each case.

In this paper, the problem of unsteady mixed convection boundary layer flow of a viscous incompressible fluid near the stagnation-point on a vertical permeable plate with both cases of prescribed wall temperature and prescribed wall heat flux is investigated numerically. Here, both assisting and opposing buoyancy forces are considered and studied. The nonlinear coupled partial differential equations governing the flow, thermal and concentration fields are first transformed into a set of nonlinear coupled ordinary differential equations by a set of suitable similarity transformations. The resulting system of coupled nonlinear ordinary differential equations is solved numerically using the Runge–Kutta scheme coupled with a conventional shooting procedure.Numerical results are obtained for the skin-friction coefficient, Nusselt number and Sherwood number as well as for the velocity, temperature and concentration profiles for some values of the governing parameters, namely, the unsteadiness parameter A, permeability parameter f0 and mixed convection parameter λ. It is found that dual solutions exist for both assisting and opposing flows, and the range of the mixed convection parameter for which the solution exists, increases with suction and unsteadiness parameters.