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Turbulent mixing of two co‐axial jets having a low annular to core area ratio is enhanced by employing a chute mixer, directing part of the annular stream at 10° towards the core region. Aims to present results from measurements of time‐averaged and fluctuating components of velocity under cold flow conditions.

Experiments were conducted at a bypass ratio of 0.47 which is a typical value for low bypass turbofan engines. Contours of time‐averaged velocity and streamwise and transverse turbulence intensities were obtained by making detailed measurements close to the chutes. Distributions of time‐averaged velocity and turbulence intensity were obtained at different axial locations downstream of the chute mixer. Total and static pressure measurements were also performed.

The high velocity annular stream was found to quickly diffuse after entering through the chutes and mix with the core stream due to high turbulence generation. A strong transverse turbulence component enhanced the mixing of the streams. With the aid of the chute mixer, nearly complete mixing is achieved over a length of 5 duct radii. A higher total pressure loss of about 1.38 percent is the penalty paid for the enhanced mixing.

Provides results from experiments into the process of turbulent mixing of co‐axial jets.

The system studied here consists of a non‐rotating cylinder sliding inside a fully lubricated parallel track with a prescribed longitudinal velocity, carrying a transverse load (normal to the track). Reynolds equations are used for the particular case of a non‐rotating sliding cylinder in a fully lubricated track. Two short‐bearing mobility charts are developed for a normalized clearance track (equivalent to those developed by Booker for journal‐bearings). Pressure distributions around the cylinder and motion paths within the clearance track are produced for prescribed transverse loading and longitudinal speed requirements for hydrodynamic analysis purposes. Numerical application examples are presented for general and specific cases at the end.

In this paper a new method for the hydrodynamic analysis of a sliding cylinder in a lubricated parallel track is presented. The method is an extension of Booker’s “Mobility Method” (developed for cylindrical journal bearings) for the case of a non‐rotating sliding cylinder in a parallel track. In this application, the clearance between the track and the cylinder, the viscosity of the lubricant, the radius and length of the pin, the sliding velocity and the applied transverse load determine the hydrodynamic behavior of the slider cylinder. An axial positive displacement vane device is used to illustrate the applicability of the hydrodynamic mobility approach for a lubrication analysis. A rotor and a stationary cylindrical cam with cycloidal tracks drive the axicycloidal motion of vanes. A case analysis is presented for a device running at constant speed, in which the inertia forces, friction forces and direct vane loads are taken into account to determine the hydrodynamic behavior of the sliding pins. The following results are produced: pin eccentricity paths, minimum lubricant film thickness history, peak film pressure history and pressure distributions on the cylindrical at any point of the motion. Results show small departures from the purely cycloidal lift‐dwell‐return‐dwell motion of the vanes due to the hydrodynamic performance of the pins.

The purpose of this paper is to carry out a hydrodynamic and thermal analysis of turbulent forced-convection flows of pure water, pure ethylene glycol and water-ethylene glycol mixture, as base fluids dispersed by Al₂O₃ nano-sized solid particles, through a constant temperature-surfaced rectangular cross-section channel with detached and attached obstacles, using a computational fluid dynamics (CFD) technique. Effects of various base fluids and different Al₂O₃ nano-sized solid particle solid volume fractions with Reynolds numbers ranging from 5,000 to 50,000 were analyzed. The contour plots of dynamic pressure, stream-function, velocity-magnitude, axial velocity, transverse velocity, turbulent intensity, turbulent kinetic energy, turbulent viscosity and temperature fields, the axial velocity profiles, the local and average Nusselt numbers, as well as the local and average coefficients of skin friction, were obtained and investigated numerically.

The fluid flow and temperature fields were simulated using the Commercial CFD Software FLUENT. The same package included a preprocessor GAMBIT which was used to create the mesh needed for the solver. The RANS equations, along with the standard k-epsilon turbulence model and the energy equation were used to control the channel flow model. All the equations were discretized by the finite volume method using a two-dimensional formulation, using the semi-implicit method for pressure-linked equations pressure-velocity coupling algorithm. With regard to the flow characteristics, the interpolation QUICK scheme was applied, and a second-order upwind scheme was used for the pressure terms. The under-relaxation was changed between the values 0.3 and 1.0 to control the update of the computed variables at each iteration. Moreover, various grid systems were tested to analyze the effect of the grid size on the numerical solution. Then, the solutions are said to be converging when the normalized residuals are smaller than 10-12 and 10-9 for the energy equation and the other variables, respectively. The equations were iterated by the solver till it reached the needed residuals or when it stabilized at a fixed value.

The result analysis showed that the pure ethylene glycol with Al₂O₃ nanoparticles showed a significant heat transfer enhancement, in terms of local and average Nusselt numbers, compared with other pure or mixed fluid-based nanofluids, with low-pressure losses in terms of local and average skin friction coefficients.

The present research ended up at interesting results which constitute a valuable contribution to the improvement of the knowledge basis of professional work through research related to turbulent flow forced-convection within channels supplied with obstacles, and especially inside heat exchangers and solar flat plate collectors.

A hybrid computational method has been developed for the calculation of momentum and heat transfer in turbulent boundary layer flows along flat plates. The proposed method, the finite volume‐based method of lines, replaces a partial differential equation and two independent variables by a system of ordinary differential equations of first order and one independent variable. Using the simplest assumptions for modeling the turbulent diffusivity of momentum and heat, the system of differential equations may be readily integrated with a fourth‐order Runge‐Kutta algorithm. To validate the numerical predictions, comparisons with experimental data for air have been done in terms of axial velocities, temperatures, skin friction coefficients and Stanton numbers. For the wide range of Reynolds numbers tested, the hydrodynamic and thermal characteristics of turbulent air flows are predicted correctly.

The two‐dimensional steady boundary layer equations, for simultaneous heat and fluid flow within ducts, are handled through the generalized integral transform technique. The momentum and energy equations are integral transformed by eliminating the transversal coordinate and reducing the PDE’s into an infinite system of coupled non‐linear ordinary differential equations for the transformed potentials. An adaptively truncated version of this ODE system is numerically handled through well known initial value problem solvers, with automatic precision control procedures. The explicit inversion formulae are then recalled to provide analytic expressions for velocity and temperature fields and related quantities of practical interest. Typical examples are presented in order to illustrate the hybrid numerical analytical approach and its convergence behaviour.

The hydrodynamic development of non‐Newtonian fluid flow in the entrance region of a duct with porous walls is examined numerically by solving the modified Navier‐Stokes equations. Cases involving blowing, suction, and no mass transfer through the walls are considered. Velocity distributions, pressure drops, and skin friction coefficients are presents for each case. A definite concavity is found in the velocity profile near the duct entrance for all cases. Results for Newtonian fluids are compared with previous studies in which boundary‐layer theory was used. In the region away from the entrance it is found that the present results are in good agreement with previous works. In the region close to the entrance, or in the case of suction, boundary‐layer theory is shown to be inappropriate.

Computational procedures and results of an upwash jet arising from two opposing plane wall jets based on the Reynolds averaged Navier‐Stokes equations are discussed. For the calculation of the flow, a steady and an unsteady numerical approach were taken. For the steady computation, we adopted various eddy viscosity models(the standard k‐ε model, the RNG k‐ε model and the Bardina’s model) and the Reynolds stress transport model with various diffusion term closures. Results of the steady computation indicated that the jet half‐width was very much underpredicted, and hence the velocity profiles of the upwash jet were in very poor agreement with the experimental data. We found, however, that the velocity profiles nondimensionalized by the jet half width and the maximum velocity appeared to be in good agreement with the experimental data, which could be misleading. When an unsteady approach with an unsteady version of the standard k‐ε eddy viscosity model was taken, a periodic oscillation of the jet was observed. The jet half‐width distribution obtained by taking the time average of the periodic velocity profiles was found to be in much better agreement with the experimental data.

The purpose of this paper is to analyze numerically forced convective conjugate heat transfer characteristics for laminar flow through a wavy minichannel.

The mass and momentum conservation equations for the flow of water in the fluidic domain and the coupled energy conservation equations in both the fluid and solid domain are solved numerically using the finite element method. The exteriors of both the walls are subjected to a uniform heat flux.

The results reveal that the theoretical model without consideration of the effect of wall thickness always predicts a lower value of average Nusselt number ( Nu¯) as compared to the case of conjugate analysis, although it varies with the thickness as well as material of the wall. For the low amplitude of the wall (α = 0.2), the performance factor (PF) becomes very high for Re in the regime of 5 (⩽) Re (⩽) 15. For any geometrical configurations, conjugate heat transfer analysis predicts higher PF as compared to that of nonconjugate analysis.

The present study finds relevance in several applications, such as solar collectors and heat exchangers used in chemical industries and heating-ventilation and air-conditioning, etc.

To the best of the authors’ knowledge, the analysis of combined influences of the thickness and the material of the wall of the channel together with the geometrical parameters of the channel, namely, amplitude and wavelength on the heat transfer and fluid flow characteristics for flow through wavy minichannel in the laminar regime is reported first time in the literature.

Investigates numerically the mechanism of enhancing heat transfer by using porous substrate. The numerical investigation is carried out for transient forced convection in the developing region of a parallel‐plate channel partially filled with a porous medium. A porous substrate is inserted in the channel core in order to reduce the boundary layer thickness and hence, enhance heat transfer. Darcy‐Brinkman‐Forchheimer model is used to simulate the physical problem. Results of the current model show that the existence of the porous substrate may improve the Nusselt number at the fully developed region by a factor of four and even higher depending on the value of Darcy number. It is found that the maximum Nusselt number is achieved at an optimum thickness. Also, the study shows that partially filled channels have better thermal performance than the totally filled ones. However, there is an optimum thickness of porous substrate, beyond it the Nusselt number starts to decline.