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A turbulent plane jet impinging on a slotted surface is simulated using Large Eddy Simulation LES. The Reynolds number, based on the jet-exit velocity and width, is equal to 5435. The slotted surface is placed at a distance equal to four times the jet-exit width. Three computational grids were used to assess the accuracy of the LES simulations conducted. The interaction effects of the jet with the slot propagate away from the slot region and manifest into pressure perturbations. Interesting phenomena were observed when linking the dynamic flow features upstream and downstream of the slotted surface. LES predicted three dominant frequencies at different points from time signals of velocities and pressure. The dominant frequency of the pressure field, away from the slot, corresponds to that of coherent vortices which follow a trajectory that is far from being deviated towards the wall jet or into the slot of the impingement wall completely. Among these turbulent structures of interest, pairs of opposite, but in phase, vortices are responsible for promoting the occurrence of the throttling phenomenon. The characteristic frequencies of the pressure field are similar upstream and downstream of the impingement wall. The peaks of the fluctuating pressures, away from the slot, correlate well with the minimum flow rate through the slot which correspond to the throttling phenomenon.

Numerical computation of thermally developing laminar flow of viscoelastic FENE-P fluids flowing between two stationary parallel plates is investigated using the finite element technique. The influence of the effect of the solvent contribution as well as the fluid rheology on the flow field and heat transfer enhancement is investigated for the case of imposed constant wall heat flux and neglected viscous dissipation. Numerical results for flow field are compared first against available analytical solutions with and without inclusion of the solvent contribution. The obtained results for the viscoelastic case show that increasing Weissenberg number (We) leads to an increase in Nusselt number (Nu) while high values of the extensibility parameter (L2) decrease the Nusselt number. Fully developed Nusselt number values for FENE-P fluids flowing between two fixed parallel plates are obtained for several values of polymer concentration and the study confirms quantitatively that polymer concentration enhances heat transfer rates in FENE-P fluids.

Steady two-dimensional natural convection in fluid filled cavities is numerically investigated for the case of non-Newtonian shear thickening power law liquids. The conservation equations of mass, momentum and energy under the assumption of a Newtonian Boussinesq fluid have been solved using the finite volume method for Newtonian and non-Newtonian fluids. The computations were performed for a Rayleigh number, based on cavity height, of 10(5) and a Prandtl number of 100. In all of the numerical experiments, the channel is heated from below and cooled from the top with insulated side-walls and the inclination angle is varied. The simulations have been carried out for aspect ratios of 1 and 4. Comparison between the Newtonian and the non-Newtonian cases is conducted based on the dependence of the average Nusselt number on angle of inclination. It is shown that despite significant variation in heat transfer rate both Newtonian and non-Newtonian fluids exhibit similar behavior with the transition from multi-cell flow structure to a single-cell regime.

Numerical investigations of purely-elastic instabilities occurring in creeping flows are reported in planar cross-slot geometries with both sharp and round corners. The fluid is described by the upper-convected Maxwell model, and the governing equations are solved using the finite element technique based on a steady (non-iterative) direct solver implemented in the POLYFLOWcommercial software (version 14.0). Specifically, extensive simulations were carried out on different meshes, with and without the use of flow perturbations, for a wide range of rheological parameters. Such simulations show the onset of flow asymmetries above a critical Deborah number (De). The effect of rounding the comers is also addressed. The numerical results obtained are found to be in good quantitative agreement with previously published numerical results

Abstract Parameters affecting the performance of de-oiling hydrocyclones are related to geometry, flow, and the fluids to separate. Global assessment studies have been conducted since the invention of the device in the 1980s, while the internal flow field still deserves exploration. The present work investigates the multi-phase flow behaviour of a de-oiling hydrocyclone using computational fluid dynamics. The Reynolds stress and the renormalization group k—ε turbulence models combined with the multi-phase mixture model, implemented in the commercial code FLUENT, were employed to predict the different features of the complex multi-component flow inside the hydrocyclone. Profiles of the velocity components and the Reynolds stresses revealed interesting explanations of the effects of feed flowrate, feed oil concentration, and oil droplet size on the separation efficiency, which is the most important performance indicator. Pressure drop and friction coefficient results are also presented and discussed.

This paper presents an experimental study of laminar flow past a smoothed hemisphere using the Particle Image Velocimetry technique. The experimental setup consists of a rectangular channel, through which water flows over a 30-mm diameter hemisphere mounted on a horizontal surface. From the measured velocity distribution around the hemisphere a physical insight into the flow is presented. Vertical and horizontal 2D velocity distributions are obtained for a constant Reynolds number of Re=800, corresponding to a regime of laminar flow. Measurements revealed the three dimensional structure of the flow including a horseshoe vortex surrounding the hemisphere and arch-shaped vortices in the downstream region. Both instantaneous and average velocity distribution were studied. The location of the reattachment point, the separation line, and the reverse flow are identified and discussed.

Steady two-dimensional natural convection in fluid filled cavities is numerically investigated for the case of non- Newtonian shear thickening power law liquids. The conservation equations of mass, momentum and energy under the assumption of a Newtonian Boussinesq fluid have been solved using the finite volume method for Newtonian and non-Newtonian fluids. The computations were performed for a Rayleigh number, based on cavity height, of 105 and a Prandtl number of 100. In all of the numerical experiments, the channel is heated from below and cooled from the top with insulated side-walls and the inclination angle is varied. The simulations have been carried out for aspect ratios of 1 and 4. Comparison between the Newtonian and the non-Newtonian cases is conducted based on the dependence of the average Nusselt number on angle of inclination. It is shown that despite significant variation in heat transfer rate both Newtonian and non-Newtonian fluids exhibit similar behavior with the transition from multi-cell flow structure to a single-cell regime.

Steady two-dimensional natural convection in fluid filled cavities is numerically investigated for the case of non-Newtonian shear thickening power law liquids. The conservation equations of mass, momentum and energy under the assumption of a Newtonian Boussinesq fluid have been solved using the finite volume method for Newtonian and non-Newtonian fluids. The computations were performed for a Rayleigh number, based on cavity height, of 10(5) and a Prandtl number of 100. In all of the numerical experiments, the channel is heated from below and cooled from the top with insulated side-walls and the inclination angle is varied. The simulations have been carried out for aspect ratios of 1 and 4. Comparison between the Newtonian and the non-Newtonian cases is conducted based on the dependence of the average Nusselt number on angle of inclination. It is shown that despite significant variation in heat transfer rate both Newtonian and non-Newtonian fluids exhibit similar behavior with the transition from multi-cell flow structure to a single-cell regime.

Abstract An experimental study was made of an incompressible flow through a model S-shaped semicircular to circular transition diffusing duct. The transition diffuser has a length—exit diameter ratio of 3 and a duct offset ratio of 0.3. The operating Reynolds number based on hydraulic diameter and bulk velocity is 40 000. The refraction index matching technique and laser Doppler velocimetry were used for velocity measurements. The measurements indicate that flow distortion persists at the outlet and the separation of the boundary layers is incipient. Semicircular to circular transition duct flow was studied in order to document the transition duct flow field and to provide detailed duct flow data for comparison with numerical code prediction. Experimental results also suggest that details of the near-wall flow incipient separation region and the distortion of the flow in the second half of the diffuser are likely to provide a severe test for various computational methods and turbulence models.

Introduction. Voltage sag, which is associated to a transitory drop in the root mean square voltage characterizing an electrical source network. During these perturbations, the corresponding electronic customers and devices will suffer from serious operating troubles causing dangerous damages. Purpose. In order to attenuate this disturbance effects, the Controlled Dynamic Voltage Restorer constitutes a very interesting solution among many others that have been proposed. The novelty of the proposed work consists in presenting an enhanced algorithm to control efficiently the dynamic voltage restorer when voltage sag is suddenly occurred. Methods. The proposed algorithm is based on an instantaneous phase locked loop using a multi variable filter to synthesize unitary signals involved in compensation voltages computation relative to the sag apparition. Practical value. A detailed study concerning typical voltage sag, which is consolidated by simulation and experimental results, is conducted to show the used algorithm’s effectiveness to cancel the corresponding voltage sag.