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In this work, the Large Eddy Simulation (LES) methodology is used to study the effects of a periodic perturbation introduced into a separated shear layer behind a backward-facing step. This study carried out by acting on the two parameters characteristics of the perturbation: frequency and amplitude. The obtained results reveal the existence of an optimum perturbation frequency value, Stp = 0.25, in terms of the reduced reattachment length. At this perturbation frequency value, we observed an increase in the vortical shedding frequency in the reattachment zone with a significant change of the structure of the flow. The value of the optimum frequency appears to be independent of the perturbation amplitude. At this frequency the maximum decrease of reattachment length is 50% and the maximum increase of vortical shedding frequency is 43 % compared to the unperturbed case.

The prediction of sedimentation is an important aspect of reservoir planning and design. Such prediction can be supported by detailed analyses of flow patterns and sediment transport inside reservoirs, usually conducted through numerical simulation. This research compares laboratorial sedimentation experiments in a shallow reservoir and predictions using a 2D numerical model with depth-average Navier-Stokes equations and a sediment transport code. A number of sediment transport equations were tested, among which the Engelund and Fredsøe formulation better represented the measured data. Flows without sediment transport or without bed dunes could be simulated using Smagorinski’s turbulence model, while flows with sediment occurring over dunes needed the use of a constant turbulent viscosity. The similarity obtained between experimental data and numerical results, for both flow pattern and sediment deposition, confirms that the models and numerical codes used in this work are useful for the analysis and prediction of reservoir sedimentation.

This paper deals with the investigations of the in-cylinder flow pattern around the intake valve of a single-cylinder internal combustion engine using Particle Image Velocimetry (PIV) at different intake air flow rates. The intake air flow rates are corresponding to the three engine speeds of 1000, 2000 and 3000 rev/min., at all the static intake valve opening conditions. In this study, in-cylinder flow structure is characterized by the tumble ratio and maximum turbulent kinetic energy of the flow fields. In addition, at two specified lines of the combustion chamber, the radial and axial velocity profiles have been plotted. From the results, it is found that the overall airflow direction at the exit of the intake valve does not change significantly with the air flow rate and intake valve opening conditions. The tumble ratio increases with increase in intake valve opening and not much affected by the change in the air flow rates. It is also found that, the variations of the velocity profiles at the two specified lines are smooth at full intake valve opening irrespective of the air flow rate. Also, their magnitudes increase with increase in the intake valve openings at all the air flow rates. The in-cylinder flow analysis carried out in this study may be useful for optimizing the intake valve opening of an internal combustion engine with respect to it’s speed.

A control-volume numerical approach has been used to study rarefaction effects in simultaneously hydrodynamically and thermally developing flow in rectangular microchannels with a prescribed uniform wall heat flux in the slip-flow regime (10-3 ≤ Kn ≤ 10-1). The effects of velocity slip and thermal creep on the key flow parameters are examined in detail. Low Reynolds number flows (Re ≤ 1) for different channel aspect ratios (0 ≤ α* ≤ 1) are considered. The effects of rarefaction on the global features of the flow and thermal development in the entrance region are examined. Dramatic reductions in the friction coefficient are observed in the entrance region due to rarefaction effects, which are enhanced by thermal creep. For the fluid heating cases considered here, thermal creep increases slip at the wall and thereby further reduces the friction coefficient and slightly enhances heat transfer at a given Reynolds number. For an identical heat flux applied to the microchannel walls, thermal creep effects become much more pronounced at lower Reynolds numbers since it results in higher axial temperature gradients.

studied numerically. The left vertical wall of the cavity is heated with a temperature varying sinusoidally in time, while the opposite cold wall is maintained at a constant temperature. The same walls of the cavity are salted with constant and different concentrations (the concentration of the heated wall is higher than that of the cooled one). The remaining horizontal walls are considered adiabatic and impermeable. The parameters governing the problem are the amplitude of the variable temperature (0 £ a £ 1), its period (0.0001 £ t £ 10), the buoyancy forces ratio (-5 £ N £ +5), the Lewis number (0.1 £ Le £ 10) and the thermal Darcy-Rayleigh number (RT = 400). Effects of these parameters on fluid flow, temperature and concentration distributions and mean heat and mass transfers within the cavity are analyzed. Results obtained show that both heat and mass transfers could be significantly enhanced or reduced, with respect to those generated in the case of constant heating conditions by proper choice of the parameters related to the periodic temperature.

Supersonic flow over a tapered body of revolution has been investigated both experimentally and numerically. The experimental study consisted of a series of wind tunnel tests on an ogive-cylinder body. Static pressure distributions on the body surfaces at several longitudinal cross sections, as well as the boundary layer profiles at various angles of attack have been measured. Further, the flow around the model was visualized using Schlieren technique. Tests with a natural development of the boundary layer and with tripping were also carried out. All tests were conducted in the trisonic wind tunnel of Qadr Research Center. Our results show that artificial boundary layer tripping has minor effect on the static surface pressure distribution (depending on its diameter and installation location), while the changes in total pressure around the body were significant. Tripping the boundary layer increased its thickness, changed its profile particularly near the body surface. Two oblique shock waves were formed in the front and behind the trip wire. In this study, using multi-block grid, the thin layer Navier-Stokes (TLNS) equations were solved around the above models. Also patched method was used near the interfaces. Good agreements were achieved when the numerical results were compared with the corresponding experimental data.

A combined convection process between two parallel vertical infinite walls, containing an incompressible viscous fluid layer and a fluid saturated porous layer has been presented analytically. There is a vertical axial variation of temperature in the upward direction along the walls. The Brinkman extended Darcy model is applied to describe the momentum transfer in the porous region. The viscosity of the fluid layer and the effective viscosity of the porous layer are assumed to be different. Also the thermal conductivities of both fluid and porous layers are assumed to be different. The graphs and tables have been used to distinguish the influence of distinct parameters on the velocity and skin-friction. It is determined that the velocity is intensified on making greater the temperature difference between the walls while increment in the viscosity ratio (porous/fluid) parameter diminishes the velocity of the fluid. It has been observed that the numerical values of the skin-frictions have an increasing tendency with the increment in the values of temperature difference between the walls while decreasing tendency with the increment in the viscosity ratio parameter (porous/fluid).

This paper deals with a numerical simulation of natural convection flows in a prismatic cavity. This configuration represents solar energy collectors, conventional attic spaces of greenhouses and buildings with pitched roofs. The third dimension of the cavity is considered long enough for the flow to be considered 2D. The base is submitted to a uniform heat flux, the two top inclined walls are symmetrically cooled and the two vertical walls are assumed to be perfect thermal insulators. The aim of the study is to examine the thermal exchange by natural convection and effects of buoyancy forces on flow structure. The study provides useful information on the flow structure sensitivity to the governing parameters, the Rayleigh number (Ra) and the aspect ratio of the cavity. The hydrodynamic and thermal fields, the local Nusselt number, the temperature profile at the bottom and at the center of the cavity are investigated for a large range of Ra. The effect of the aspect ratio is examined for different values of Ra. Based on the authors’ knowledge, no previous results on natural convection in this geometry exist.

The purpose of this study is to analyze the fluid flow and heat transfer in a pipe partially filled with porous media and provided with a flat piston during an expansion stroke. In addition to the Navier-Stokes equation for the fluid region, Brinkman-Forchheimer-Lapwood-extended Darcy’s model is introduced into the numerical solver to simulate flow and heat transfer in the porous insert. The heat transfer in porous media is studied by using the assumption of local thermal equilibrium. The discretization procedure is based on Control-Volume-based Finite Element Method. The coupled pressure-velocity equations are solved using the SIMPLER algorithm. This investigation concerns the hydrodynamic characteristics, using the Reynolds numbers and the porosity effects, and the heat transfer characteristics using the heat capacity and the thermal conductivity ratios effects.

The objective of this study is to analyze the behavior of an energy storage system which is made of a horizontal channel crossed by a fluid and whose walls contain an unsaturated porous medium. We developed a threedimensional model to study the two processes: thermal energy charging and thermal energy discharging. The coupled and highly non linear nature of the transport equations that govern the heat and mass transfer inside unsaturated medium were discretized by control volume finite element method (CVFEM). The resulted system of algebraic equations was solved by the Bi-Conjugate Gradient Stabilized iterative solver. Results concerning the influence of the initial liquid saturation on the rate of charged and discharged thermal energy are presented and analyzed.

In this paper a comprehensive review of flow visualization techniques used for the analysis of spray characteristics is presented and an experimental demonstration of different lighting techniques has been made. Still photographs of sprays from an airblast atomizer and a swirl atomizer are taken under backlighting, slit lighting, incident lighting (front flash) and a new method of capturing scattered light image at 1200 to the incident light is introduced in the present work. Photographs taken by these methods are shown to be useful for deriving useful observations such as jet breakup phenomenon, the internal details and the external appearance of the spray. It is demonstrated that the information obtainable from each technique is different and that a combination of different techniques may be necessary for proper diagnosis. The article also includes a discussion on the jet breakup phenomenon as observed in the photographs and in addition a new concept of shear formation of smaller droplets from the surface of a liquid jet by the co-flowing air stream in an airblast atomizer has been proposed.

The megathrust earthquake of moment magnitude 9.1 – 9.3 on December 26, 2004 unleashed a massive tsunami which devastated the coastal belts of Sri Lanka as well as several other countries bordering the Indian Ocean. Extensive field observations carried out in Sri Lanka in the aftermath of the tsunami clearly showed that the spatial variation of the degree of destruction along the coastal belt was highly non-uniform. The coastal geomorphology, for instance, the presence of sand dunes in some parts of the coast, is one primary factor that had contributed to this nonuniformity. Accordingly, the present paper investigates, as a case study, the effect of a nearly 2 km long sand dune, lying along a part of the seafront of a city on the south coast of Sri Lanka, on the characteristics of the spatial distribution of inundation. Numerical simulations based on non-linear shallow water equations were carried out first with the sand dune and then without the dune to obtain the respective spatial distributions of the maximum values of the depth of inundation and the flow velocity as well as their temporal variations. The results appear to indicate that the peak flood flow rates and flow depths are higher in most areas of the city in the case without the dune compared to that with the dune. However, it appears that the tsunami surge backing up against the sand dune and other elevated beachfronts causes a rise in water level of up to 0.5 m in the case with the sand dune compared to that without the dune. Flow velocities in the absence of the dune too appear to be higher in most areas although there are patches of lower velocities at certain low elevation localities with elevated ground on either side.