JOURNAL OF APPLIED FLUID MECHANICS (JAFM)
Year:2008 | Volume:1 | Issue:1|Papers Count:7

The sudden release of a mass of fluid in a channel generates a highly unsteady flow motion, called dam break wave. While industrial fluids exhibit sometimes non-Newtonian behaviors, the viscous fluid flow assumption remains a useful approximation for simplified analyses. In this study, new solutions of laminar dam break wave are proposed for a semi-infinite reservoir based upon the method of characteristics. The solutions yield simple explicit expressions of the wave front location, wave front celerity and instantaneous free-surface profiles that compare favorably with experimental observations. Both horizontal and sloping channel configurations are treated. The simplicity of the equations may allow future extension to more complicated fluid flows.

Sea surface brightness spectral anomalies from a Honolulu municipal outfall have been detected from space satellites in 200 km2 areas extending 20 km from the wastewater diffuser (Leung and Gibson 2004, Bondur 2005, Keeler et al. 2005, Gibson et al. 2006). Dropsonde and towed body microstructure measurements show greatly enhanced viscous and temperature dissipation rates above the outfall trapping-layer. Fossil-turbulence waves (FTWs) and secondary zombie-turbulence-waves (ZTWs) break as they propagate near-vertically and then break again near the surface to produce wind-ripple smoothing with narrow-wavelength l patterns from the soliton-like internal waves that supply turbulence energy to advected outfall fossils and to the ZTWs they radiate. The l= 30-250 m solitons reflect an efficient maser-action conversion of horizontal tidal and current kinetic energy by bottom boundary layer turbulence events to near-vertical FTWs with l the Ozmidov scak of the events at fossilization. Secondary (zombie) turbulence amplifies, channels in chinmeys, and near-vertically beams ambient internal wave energy at scales l just as energized metastable molecules amplify and beam quantum wavelengths in astrophysical lasers and masers around stars. Kilowatts of buoyancy power from the treatment plant produce fossil turbulence patches trapped below the thermocline. Beamed zombie turbulence maser action (BZTMA) in mixing chinmeys amplifies these kilowatts into the megawatts of surface turbulence dissipation required to affect brightness on wide sea surface areas. The BZTMA vertical mixing mechanism appears critical to vertical oceanic transport of information, heat, mass and momentum, and to the conversion of barotropic tides to baroclinic tides.

Circulation regions always exist in settling tanks. These regions reduce the tank's performance and decrease its effective volume. The recirculation zones would result in short-circuiting and high flow mixing problems. The inlet position would also affect the size and location of the recirculation region. Using a proper baffle configuration could substantially increase the performance of the settling tanks. A common procedure for the comparison of the performances of different tanks has been using the Flow Through Curves (FTC) method. FTC, however, neglects tendencies for particles sedimentation. In this work, a new method for evaluation of the settling tanks performance is presented. The new method which is referred to as the particle Tracking Method (PTM) is based on an Eulerian-Lagrangian approach. In this paper, by using FTC and PTM the effects of the inlet position and the baffle configuration on the hydraulic performance of the primary settling tanks were studied and results were compared. Then, shortcomings of the FTC approach were stated. The optimal positioning of the baffles was also determined though a series of computer simulations.

In pumping installations, fluid transient computations are necessary to achieve safety, efficiency and economy in design and operation. In some systems, where air content and air entrainment exist, such computations become highly inaccurate when constant wave speed is assumed. In this paper, a numerical model and a computational procedure have been developed to investigate the effects of air entrainment on the pressure transient in pumping systems. Free gas in the fluid and cavitations at the fluid vapour pressure were modeled in the form of variable wave speed model, which was numerically solved by the method of characteristics. This model was tested for the case of pump trips due to power failures. The pressure transient results obtained by this variable wave speed model were analyzed and compared with those results obtained by constant wave speed p10deland with the experimental results of other investigators.

Many types of chemical substances have been used as tracers to estimate the migration of contaminant in a porous media. Inorganic ionic compounds have been applied extensively as hydrogeologic tracers. Sodium chloride is generally used as a tracer since this common salt does not degrade or get removed from the system. Movement of tracer could be described as migration of a non-reactive constituent. A tracer transport numerical model was developed according to the advective dispersive contaminant transport equation in unsaturated porous media. The governing equation was solved numerically and coded in MATLAB program. The objectives of this study were to develop a model for estimating the non-reactive constituent transport in the unsaturated porous media and to determine the impact of ionic strength of tracer and the effect of the thickness of porous media. The experiments were conducted with two different sodium chloride tracer concentrations (low strength-200 mg/L and high strength-500 mg/L) and for two different soil depths (5 and 20 cm). The observation and simulation data indicate that the interference from soil background concentration is significant, provided that the high strength tracer is applied. As expected, the tracer transport in the thick layer took longer elapse time than in the thin layer. The simulation results using the developed model corresponded very well with the observed data.

This paper was presented at the Eleventh Asian Congress of Fluid Mechanics as an invited/keynote lecture. The lecture summarizes development of physical model for transfer processes in turbulent separated flows. Attention is focused on the factors that have led to significant advances in understanding of the mechanisms of transfer processes in separated flows, which differs from those in traditional attached turbulent flows in channels and zero pressure gradient turbulent flows. The physical model of transfer processes in the near-wall region of turbulent separated and reattached flows based on the assumption of the governing role of generated local pressure gradient that takes place in the immediate vicinity of the wall in separated flow as a result of intense instantaneous accelerations induced by large-scale vortex flow structures is discussed. Similarity laws for mean velocity and temperature profiles and spectral characteristics of the transfer processes resulting in the physical model are confirmed by the available experimental data. The physical model has provided explanations of the well-known empirical heat and mass transfer correlations for turbulent separated flows and other types of flows close in their structure to those of turbulent separated flows.

A numerical analysis is carried out to study the performance of mixed convection in a rectangular enclosure. Four different placement configurations of the inlet and outlet openings were considered. A constant flux heat source strip is flush-mounted on the vertical surface, modeling an integrated circuit chips affixed to a printed circuit board, and the fluid considered is air. The numerical scheme is based on the finite element method adapted to triangular non-uniform mesh elements by a nonlinear parametric solution algorithm. Results are obtained for a range of Richardson number from 0 to 10 at Pr= 0.71 and Re = 100 with constant physical properties. At the outlet of the computational domain a convective boundary condition (CBe) is used. The results indicate that the average Nusselt number and the dimensionless surface temperature on the heat source strongly depend on the positioning of the inlet and outlet. The basic nature of the resulting interaction between the forced external air stream and the buoyancy-driven flow by the heat source is explained by the heat transfer coefficient and the patterns of the streamlines, velocity vectors and isotherms.