Journal Of Applied Fluid Mechanics
Volume:2 Issue: 2, May-Jun 2009

Several existing equations for solving the non-linear soil-hydraulic properties are introduced and validated to field and laboratory measured data. Models for non-linear hydraulic properties of unsaturated porous media arise from statistical and mathematical fit through the measured data and they can be expressed in forms of unsaturated permeability versus either pressure head or volumetric moisture content. This paper presents the difference models: Gardner, Knuze et al., Haverkamp et al., van Genuchten and Saxton et al. for calculation of hydraulic properties coefficients, typically unsaturated permeability. The accurate and computational efficiency of these five existing models are evaluated for a series of study cases simulating hydraulic properties of unsaturated porous media. The results indicate that all existing models can be applied to homogenous and heterogenous unsaturated porous media, dry and wet cycles and laboratory and field measuring data. Besides, the statistical fit model is inefficient compared to mathematical fit models. Among the mathematical fit models, van Genuchten model is the most promising model. Gardner model can be competitive with van Genuchten model and Haverkamp et al. model is less efficient than others. The mathematical fit models appear to be attractive alternatives to estimate the unsaturated permeability, although there are concerns regarding the stability behaviour of the occupied air in pores, which need to be resolved. The air movement in unsaturated porous media affected the unsaturated permeability, which gives the difference results between wet and dry cycle. Both of unsaturated permeability and volumetric water content of dry cycle were higher than ones of wet cycle. This suggests that the velocity of air-releasing during a wet process was higher than the velocity of air-entering during a dry process. The infiltration is the most important land applications. So, the wet cycle hydraulic properties test might be concerned. Moreover, most of infiltration fields locate on the mixed grain media. So too, the pore-size distribution could affect the unsaturated permeability of porous media. It was observed that the finer material, the lower unsaturated permeability.

CFD (Computational Fluid Dynamics) Analysis of Delta wing configurations used for supersonic flight regime is a key area of interest for flow control due to coherent vortical structures existing on the leeward side of wing. In the present research, a numerical study was carried out by using two different turbulence models at Mach No. 1.6, to identify the influence of turbulence modeling and wing on overall pressure distribution and onset of flow separation. Fully structured multi-block grid was used with the grid refinement near the wall to resolve the vortical flow structures accurately. Different turbulence models used were SA (Spalart-Allmaras) and kω-SST (Shear-stress Transport). An under prediction in pressure distribution was observed by using SA Turbulence model, in comparison with known experimental data at fixed Mach No. The analysis of results presented showed that the height of primary vortex increases by increasing the angle of attack and by keeping the Mach No. as fixed. Moreover, the vortex formation on cambered wing seems less pronounced as compared with that of sharp wing at high angle of attack.

Electromagnetic pumps have several advantages to mechanical pumps. They offer maneuverability by directional thrust along with quietness and are conceived with an aim of eliminating all moving parts, being also free from problems of wear and tiredness of use. The flow field in the channel is treated as steady state, incompressible and fully developed laminar flow conditions. Our numerical code DCPMHD uses cylindrical coordinates (r,phi, z) and solves the incompressible MHD equations for magnetic vector potential A and fluid velocity V. Using finite volume method for numerical calculation. The numerical results of the performance characteristics of a DC electromagnetic pump are discussed and show that our new concept is capable to deliver bi-directional activation and have a satisfactory controllability, because of its proportional output force and input current relationship.

Radiation effects on boundary layer flow and heat transfer of a fluid with variable viscosity along a symmetric wedge is presented here. Fluid viscosity is assumed to vary as a linear function of temperature. The symmetry groups admitted by thecorresponding boundary value problem are obtained by using a special form of Lie group transformations viz. scaling group of transformations.A third order and a second order coupled ordinary differential equation system corresponding to the momentum and the energy equations are obtained. These equations are then solved numerically.With the increase of temperature-dependent fluid viscosity parameter (i.e. with decreasing viscosity), the fluid velocity increases up to the cross-over point (η =η 0) (η 0 ≈ 0.90 is the nearest numerical value of the cross-over point) and after the crossing over point the fluid velocity is found to decrease but the temperature increases at a particular point.The significant finding of this study is that, due to variable fluid viscosity, flow separation is controlled. The temperature decreases with increasing value of radiation parameter and Prandtl number.

Self gravitational fluid mechanical methods termed hydrogravitational-dynamics (HGD) predict plasma fragmentation 0.03 Myr after the turbulent big bang to form protosuperclustervoids, turbulent protosuperclusters, and protogalaxies at the 0.3 Myr transition from plasma to gas. Linear protogalaxyclusters fragment at 0.003 Mpc viscous-inertial scales along turbulent vortex lines or in spirals, as observed. The plasma protogalaxies fragment on transition into white-hot planet-mass gas clouds (PFPs) in million-solar-mass clumps (PGCs) that become globular-star-clusters (GCs) from tidal forces or dark matter (PGCs) by freezing and diffusion into 0.3 Mpc halos with 97% of the galaxy mass. The weakly collisional non-baryonic dark matter diffuses to Mpc scales and fragments to form galaxy cluster halos. Stars and larger planets form by binary mergers of the trillion PFPs per PGC, mostly on 0.03 Mpc galaxy accretion disks. Stars deaths depend on rates of planet accretion and internal star mixing. Moderate accretion rates pro-duce white dwarfs that evaporate surrounding gas planets by spin-radiation to form planetary nebulae before Supernova Ia events, dimming some events to give systematic distance errors, the dark energy hypothesis, and overestimates of the universe age.

In our study we are interested with the DC (Direct Current) electric corona discharge created between two wire electrodes. We present experimental results related to someelectroaerodynamic actuators based on the DC corona discharge at the surface of a dielectric material.We used different geometrical forms of dielectric surface such as a plate, a cylinder and a wing of aircraft of type NACA 0015. We present the current density-electric filed characteristics for different cases in order to determine the discharge regimes. The corona discharge produces non-thermal plasma so that it is called plasma discharge. Plasma discharge creates a tangential ionic wind above the surface at the vicinity of the wall. We have measured the ionic wind induced by the corona discharge in absence of free external airflow, we give the ionic wind velocity profiles for different surface forms and we compare the actuators effect based on the span of the ionic wind velocity values. We notice that the maximum ionic wind velocity is obtained with the NACA profile, which shows the effectiveness of this actuator for the airflow control.

Mechanical effects can influence significantly electricalperformance and life time of PEM fuel cells.A linear elasticplastic 2D model of fuel cell with hardening is used for modeling of assembly procedure of fuel cells. The model simulates mechanical behavior of the main components of real fuel cell (the membrane, the gas diffusion layers, the graphite plates, and the seal joints) and clamping elements (the steel plates, the bolts, the nuts). The stress and plastic deformation in MEA have been calculated using ABAQUS code. The results are presented on the local and the global scales with respect to the realistic clamping conditions. The first one corresponds to the single tooth/channel structure.The global scale deals with features of the entire cell and takes into account the border effects, in particular the influence of seal joints.

Power plants using conventional processes and unconventional fluids have a significant potential for the valorization of low and medium temperature renewable energy sources as well as waste heat from industrial, commercial or institutional installations. This review paper describes some prototypes of such power plants and summarizes some of the relevant scientific and technical literature. An analysis based on the first and second laws of thermodynamics and basic heat transfer relations is used to illustrate the operational limits and performance characteristics of these power plants.

Sustainable development associated with the need to reduce the energy consumption and to offer more creative freedom to the automobile designers requires looking for new solutions of control without appendix added nor geometrical modification. Among these solutions, the active flow control by fluidic actuators constitutes an interesting alternative.Various configurations of control are thus tested in order to reduce the aerodynamic drag. The results show that protocols based on control by suction, blowing or intermittent jet allows reducing the aerodynamic drag and consequently the consumption and CO2 emissions.

In the Boundary Element Method (BEM), the corner elements make some difficulties in the numerical method.It means that, the results of BEM solution with linear elements are more accurate than constant elements inherently, but the difference between boundary conditions of one corner node from two adjacent boundaries causes to increase errors in linear element in comparison of constant element. In this article, a new approach of BEM discretizing has been introduced for simulating water sloshing in a 2D rectangular container which augments the accuracy. The time history of free surface shape has been obtained by applying Finite Difference Method (FDM) for free surface boundary conditions and BEM direct method with constant, linear and a novel element which has been named composed element in this study. Composed elements have been proposed for solving corner nodes problem. It means that all of the elements are linear except common nodes in two adjacent boundaries which are selected constant. This solution causes to decrease the number of elements for an acceptable precision and hence the time considerably saves potential flow and small amplitude water wave assumptions were applied in the present research. The results of this analysis illustrated acceptable agreement with other articles results with large dimension and small amplitude water wave assumptions. As a final point, the accuracy of results increased respect to linear, constant and composed elements.