Journal Of Applied Fluid Mechanics
Volume:4 Issue: 1, Jan-Feb 2011

Now-a-days, the stratified and direct injection spark ignition engines are becoming very popular because of their low fuel consumption and exhaust emissions. But, the challenges to them are the formation and control of the charge which is mainly dependent on the in-cylinder fluid flows. Today, an optical tool like particle image velocimetry (PIV) is extensively used for the in-cylinder fluid flow measurements. This paper deals with the experimental investigations of the in-cylinder fluid tumble flows in a motored internal combustion engine with a flat piston at different engine speeds during intake and compression strokes using PIV. The two-dimensional in-cylinder flow measurements and analysis of tumble flows have been carried out in the combustion space on a vertical plane at the cylinder axis. To analyze the fluid flows, ensemble average velocity vectors have been used. To characterize the tumble flow, tumble ratio has been estimated. From the results, it is found that the tumble ratio mainly varies with crank angle positions. At the end of compression stroke, maximum turbulent kinetic energy is more at higher engine speeds. Present study will be very useful in understanding the effect of engine speeds on the in-cylinder fluid tumble flows under real engine conditions.

Thermal radiation effects on MHD flow past an impulsively started vertical plate in the presence of heat source/sink is investigated, by taking into account the heat due to viscous dissipation. The governing boundary layer equations of the flow field are solved by an implicit finite difference method of Crank-Nicholson type. A parametric study is performed to illustrate the influence of radiation parameter, magnetic parameter, Grashof number, Prandtl number, Eckert number on the velocity, temperature and concentration profiles. Also, the local and average skin-friction, Nusselt number and Sherwood number are presented graphically. The numerical results reveal that the radiation induces a rise in both the velocity and temperature, and a decrease in the concentration. Also with an increase in the heat absorption/generation parameter the velocity increases whereas the temperature decreases. The model finds applications in solar energy collection systems, geophysics and astrophysics, aero space and also in the design of high temperature chemical process systems.

When the high DC electric fields are applied to distilled water through needle electrodes, the jet flow with velocities up to 0.3 ms-1 is generated in bulk from the negative to positive electrodes. The flow direction and velocity can be modified by the design of electrodes and their arrangements. By controlling the flow patterns, new types of inkjet devices and liquid motor are developed. In inkjet devices, a set of electrodes consisting of short tube and needle is vertically placed in plastic tube and the distilled water so filled in the reservoir that the electrodes are completely immersed. The application of high voltages causes the vertical flow to produce a water column with free surface. The motor consists of vane wheel, cup, two sets of electrodes, and working fluid. For aqueous solutions of ethanol and glycerin, the angular velocity of motor is measured as a function of viscosity and conductivity. The high performance of motor is achieved by the solutions with viscosity of 0.85 ~ 1.7 m Pa•s and conductivity of 20 ~ 30 Sm-1. The EHD water jets have great potential in application to new fluid devices.

The most widely used desalination processes are based on membrane separation via reverse osmosis (RO) which has become an important process for desalting seawater and cleaning brackish water. The use of these processes requires an efficient control system. Consequently, it is necessary to establish a dynamic model of the system with experimental validation. This paper deals with a new modelling approach of a small photovoltaic reverse osmosis (PV-RO) desalination unit. The proposed model considers the unit as a Multi Input Multi Output (MIMO) process. The relations between the output variables and the input variables are given by the use of empirical transfer matrix. A state model of the unit is also given. Some experimental results are presented to validate the proposed model. As result, the obtained unit model can be easily used for a process control loop implementation in order to assure an optimum operating condition and to reduce the water product cost.

The aim of this study is to analyze the efficiency of a Volatile Organic Compounds (VOCs) containment system using an air curtain (push-pull type) on a manual workstation. This work combines CFD numerical simulations of the air curtain system and experimental studies on a real scale test bench. The point is to evaluate whether the actual worker protection can be replaced by an air curtain system, without weakening human safety. The new system could considerably reduce energetic consumption (ventilation, heating) and VOCs emissions into the atmosphere. Experimental studies of the flow using a Particle Image Velocimetry anemometer (PIV) have been carried out to validate the numerical model kinematics. The containment quality obtained by the model has been validated with experimental concentration fields given by a gaseous analyzer using flame ionization (FID). Numerical simulation provides an overview of the containment efficiency in the global area of the system. Thus, it is possible to evaluate numerically, but accurately, the quality of the containment of the system. Moreover, an energetic study proves the economic benefit of the push-pull system.

This article is concerned with the study of a coupling between the stationary Maxwell equations, the transient state Navier Stokes and thermal equations. The model developed computes the magnetic field using the finite element method and calculates the velocity and the temperature using the finite volume method. The paper focuses on the analysis of the flux density, the electromagnetic thrust, the electric power density, the velocity, the pressure and the temperature in the channel of the MHD pump. Effect of the frequency is also presented.

A numerical solution of the unsteady radiative free convection flow of an incompressible viscous fluid past an impulsively started vertical plate with variable heat and mass flux is presented here. This type of problem finds application in many technological and engineering fields such as rocket propulsion systems, spacecraft re-entry aerothermodynamics, cosmical flight aerodynamics, plasma physics, glass production and furnace engineering. The fluid is gray, absorbing-emitting but non-scattering medium and the Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing non-linear, coupled equations are solved using an implicit finite difference scheme. Numerical results for the velocity, temperature, concentration, the local and average skin-friction, the Nusselt and Sherwood number are shown graphically, for different values of Prandtl number, Schmidt number, thermal Grashof number, mass Grashof number, radiation parameter, heat flux exponent and the mass flux exponent. It is observed that, when the radiation parameter increases, the velocity and temperature decrease in the boundary layer. The local and average skin-friction increases with the increase in radiation parameter. For increasing values of radiation parameter the local as well as average Nusselt number increases.

An experimental study and a numerical simulation are presented concerning the three dimensional turbulent flow of air in a cyclone separator in the region underneath the vortex finder. The computations are carried out using the Fluent CFD code. The turbulence effects on the mean flow are taken into account using the standard k-ε model and the standard Reynolds stress Model (RSM). The axial and tangential mean velocity components and the turbulence intensities are measured using Laser Doppler Anemometry. The LDA system is mounted in such a way that radial traverses at different angles of the cyclone cylindrical geometry and at different axial positions could be possible. The obtained results show interesting phenomena such as the three dimensional nature of the flow behaviour, the turbulence decay and its evolution towards an isotropic state in the quasi-free vortex region as the flow proceeds downstream in the cyclone. In the region underneath the vortex finder, the surface separating the descending and the ascending streams (set of points where the axial velocity component is nil) is located approximately in the fictitious prolongation of the vortex finder cylindrical wall. The existence of a quasi-forced vortex in the central region of the cyclone surrounded by a coaxial quasi-free vortex is confirmed. The radial distance separating the central vortex and the surrounding annular vortex, at a given angle and axial position, can be clearly defined as the distance from the axis to the point of intersection between two characteristic straight lines: the first line representing, ln Ut vs ln r, of slope +1, in the quasi-forced vortex and the second line, ln Ut vs ln r, of slope -1, in the quasi-free vortex, where Ut is the tangential component of the mean velocity.

This paper numerically investigated the influence of falling height on the behavior of the skid-launching free-fall lifeboat (FFLB) in regular waves. The boat has been treated as a rigid body when the differential equations of motion for the four falling phases, i.e., sliding or ramp phase, rotation phase, free-fall phase and water entry phase of the lifeboat were solved in the time domain. The hydrodynamic characteristics of the lifeboat has been studied for different falling heights such as H = 1.5m, 1.75m and 2.00m. Horizontal and vertical excursions and the rotation of the axis of the boat have been computed at different time along with its horizontal and vertical velocities. Hydrodynamic forces and accelerations at normal and axial directions have also been determined. At first the analysis has been done in still water and then in regular wave with amplitude of 0.5m and a period of 2.0 sec. In all of the cases, effects of regular wave are shown by comparing the results with those considering the falling of FFLB into calm water.

The present paper reports numerical results of mixed convection and surface radiation within a horizontal ventilated cavity heated from below and provided with an adiabatic thin partition on the heated surface. Air, a radiatively transparent medium, is considered to be the cooling fluid. The effect of the governing parameters, which are the Reynolds number, 200  Re  5000, the relative height of the baffle, 0  Hb  0.75, and the emissivity of the walls, 0    1, on the fluid flow and heat transfer characteristics is studied in detail. The maximum and mean temperatures, the ratio, QE/QL, of the heat quantities leaving the cavity through the exit, QE, and through the left vertical cold side, QL, are also presented versus the above controlling parameters.

In this paper is reported an analytical and numerical study on double-diffusive natural convection in a non-Newtonian power-law fluid confined in a shallow horizontal rectangular enclosure submitted to uniform heat and mass fluxes along its short vertical sides, while the horizontal ones are insulated and impermeable. Here, the cases of aiding and opposing thermal and solutal buoyancy forces of equal intensities are considered. In the first part of the work the full governing equations are solved and the effects of the power-law behavior index, n, and the generalized thermal Rayleigh number,, are examined and analyzed. In the second part, an analytical solution, based on the parallel flow approximation valid in the case of a shallow cavity, is proposed and an excellent agreement of results between the two approaches is observed, which validates them mutually

Effect of radiation and mass transfer on the transient free convection flow of a dissipative past semi-infinite vertical plate with uniform heat and mass flux is analyzed, by taking into account the effect of viscous dissipation. This type of problems finds application in many technological and engineering fields such as plasma studies, petroleum industries, MHD energy generators, cooling of nuclear reactors, the boundary layer control in aerodynamics, crystal growth and furnace engineering. The Rosseland approximation is used to describe the radiative heat transfer in the limit of the optically thick fluid. The non-linear, coupled equations are solved using an implicit finite difference scheme of Crank-Nicolson type. Transient temperature, concentration and velocity profiles, local and average skin-friction coefficient, Nusselt number and Sherwood number are presented graphically and discussed. It is observed that, when the radiation parameter increases the velocity and temperature decrease accompanied by simultaneous reduction in both momentum and thermal boundary layers.

The propagation of internal electromagnetic waves in an inviscid chiral fluid in the presence of the external constraint of transverse magnetic field is investigated. These waves are shown to be generated due to the stabilizing nature of the distribution of charge density. It is shown that the effect of the external constraint of magnetic field in a chiral fluid is analogous to the effect of viscosity in ordinary fluids. The wave equation, derived from the conservation of mass and momentum together with Maxwell’s equations and suitable auxiliary equations for chiral materials, reveals the existence of a critical level (i.e., resonance level) at which the Doppler shifted frequency Ωd = 0, i.e., at the point where the basic fluid velocity matches with the phase velocity of the wave. The solution of this wave equation is obtained near and away from the critical levels from which the attenuation of waves is predicted using momentum flux. This is verified using group velocity approach.

Fire behaviour, especially its interaction with ventilation system in tunnels, is still a challenging issue for road tunnel designers. This paper presents the results of a study investigating the influence of a road tunnel ventilation system, on conventional fires. For this purpose, a 25 MW fire corresponding to a conventional fire in a road tunnel was simulated using 2D numerical modelling, for transient viscous multi-component gas at low Mach numbers to study smoke and heat propagation within a road tunnel under fire. Complete Navier-Stocks and Reynolds equations were solved using developed algorithm of numerical modelling. The results from a series of calculations were compared with results of experimental researches to examine the accuracy and stability of the calculations. The comparisons showed that the algorithm provided a good description of physical processes in selected class of flow. It was also concluded that calculation accuracy is not lower than those obtained from established simulation software programs. The stability and good convergence of the algorithm was confirmed by separate calculations with different grid patterns for the tunnel under consideration. The results revealed that the temperature at tunnel wall may rise up to 900oC. The concentration of smoke may also increase up to 95% with a burning truck. Results were applied to assess the ventilation system designed for a new long road tunnel in case of fire. The results from the study along with other information were applied to assess the designed ventilation system and to establish the suitable fire fighting and rescue plan.