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This paper aims to analyze the effect of aspect ratio A and aspect velocity ratio a on the bifurcation occurrence phenomena in lid-driven cavity by using finite volume method (FVM) and multigrid acceleration. This study has been performed for certain pertinent parameters; a wide range of the Reynolds number values has been adopted, and aspect ratios ranging from 0.25 to 1 and various velocity ratios from 0.25 to 0.825 have been considered in this investigation. Results show that the transition to the unsteady regime follows the classical scheme of Hopf bifurcation, giving rise to a perfectly periodic state. Flow periodicity has been verified through time history plots for the velocity component and phase-space trajectories as a function of Reynolds number. Velocity profile for special case of a square cavity (A = 1) was found to be in good agreement between current numerical results and published ones. Flow characteristics inside the cavity have been presented and discussed in terms of streamlines and vorticity contours at a fixed Reynolds number (Re = 5,000) for various aspect ratios (a = 0).

The numerical method is based on the FVM and multigrid acceleration.

Computations have been investigated for several Reynolds numbers and aspect ratios A (0.25, 0.5, 0.75, 0.825 and 1). Besides, various velocity ratios (a = 0.25, 0.5, 0.75 and 0.825) at fixed aspect ratios (A = 0.25, 0.5 and 0.75) were considered. It is observed that the transition to the unsteady regime follows the classical scheme of Hopf bifurcation, giving rise to a perfectly periodic state. Flow periodicity is verified through time history plots for velocity components and phase-space trajectories.

The bifurcations between steady and unsteady states are investigated.

The purpose of this paper is to present a numerical investigation on pulsating heat pipe (PHP) to study the slug velocities as a function of various parameters.

The governing equation of PHP is solved using explicit embedded Runge‐Kutta method, the Dormand–Prince pair in conjunction with MATLAB with the nomenclature 45 for the determination of displacement and the velocity of the slug.

The results show that lower fill ratio, higher diameter, higher operating temperature and higher temperature difference between evaporator and condenser for a given working fluid results in higher slug velocities, indicating higher momentum transfer and hence better heat transport.

Under steady state conditions, the design of a PHP is facilitated through the introduction of non‐dimensional numbers.

The displacement and slug velocities for additional working fluids, namely ethanol and methanol, are determined for the first time. The behaviour of non‐dimensional numbers, i.e. Poiseuille number, capillary number and Eckert number in a PHP as a function of various parameters have been studied for the first time.

As the companion paper of Part I, this paper aims to get more insight into the essence of lambda and to reveal its nature and role in the transition of lubrication states. Mixed lubrication (ML) model with micro-asperities contacts has been discussed in details in Part I.

Mimetic algorithm is used to get numerical solutions. Relationships between film thickness ratios and lubrication states transition with different external loads, rotating speeds, radial clearances, elastic modulus, surface hardness and roughness parameters are obtained.

The characteristic parameters of transitions from boundary lubrication (BL) to ML and ML to hydrodynamic lubrication (HL) are studied to determine how these parameters change with above factors. Finally, the essence and major influencing factors of lambda are summarized for such bearings.

In Part II, the authors believe that the paper presents for the first time: further insight into the essence of the lambda ratio, and its role in the lubrication states transition are given; the determinations of the characteristic parameters of transition from BL to ML and ML to HL are investigated for the first time; the characteristic parameters of transitions from BL to ML and ML to HL are also studied to determine how parameters (external load, rotating speed, radial clearance, elastic modulus, surface hardness and roughness parameter) change with above factors; a summary of the essence and major influencing factors of lambda for such bearings is given.

This paper seeks to explore the fiber orientation distribution and rheological properties of turbulent fiber suspensions flowing through a contraction.

The Reynolds averaged Navier‐Stokes equation was solved with the Reynolds stress model to get the mean fluid velocity and the turbulent kinetic energy in the turbulent flow of a contraction with rectangular cross‐section. The turbulent velocity fluctuations were represented as a Fourier series with random coefficients. Then the slender‐body theory was used to predict the fiber orientation distribution, orientation tensor, additional shear stress and first normal stress difference of suspensions in the flow.

It is found that the longer fibers tend to align the streamline easily. Increased contraction ratio results in higher fiber alignment in the direction of flow. The fibers are weakly and strongly aligned in the direction of flow in the region near the inlet and the exit, respectively. Fibers are significantly more aligned in the plane of the contraction than in the x‐z plane. Contraction ratio and fiber length were shown to strongly and weakly affect the distributions of additional shear stress and first normal stress difference.

It is the first time that the fiber orientation distribution and rheological properties of turbulent fiber suspensions flowing through a contraction have been computed numerically. The computational approach and results are valuable to the design and operation of contraction used in the industrial processes.

The purpose of this paper is to ensure adequate thermal management to remove and dissipate the heat produced by a light-emitting diode (LED) and to guarantee reliable and safe operation.

A three-dimensional (3-D) computational fluid dynamics (CFD) model was used to analyze the distribution of fluid velocities among microchannels at four different aspect ratios.

The results showed that at the same inlet flow rate, the larger the aspect ratio of the microchannels, the better the uniformity of the internal fluid velocity and thus better the heat dissipation performance on the surface of the high-power LED chip. In addition, the thermal performance of a high-power LED water cooling system with four different aspect ratios’ microchannel structures is further studied experimentally. Specifically, the coupling effect between the fluid velocity distribution in the microchannels and the heat dissipation performance of a high-power LED water cooling system is qualitatively analyzed and compared with the simulation results of the fluid velocity distribution. The results fully demonstrated that a larger aspect ratio of the microchannels results in better heat dissipation performance on the surface of the high-power LED chip.

Optimizing the structural parameters to facilitate a relatively uniform velocity distribution to improve the water cooling system performance may be a key factor to be considered.

This study aims to investigate the effect of downstream characteristics of S809 wind turbine blade with various extended flat plate (EFP) configuration. Wind farms are recently modified to improve the power production through placing number of wind turbines and locations.

A series of wind tunnel experiments were carried out to evaluate the downstream wake characteristics of the S809 airfoil attached with various EFP (EFP, A = 0.1C, 0.2C and 0.3C) at various angles of attack corresponding to free stream velocity Reynolds number (Re) = 2.11 × 105 and various turbulence intensity (TI = 5%, 7%, 10% and 12%).

For the S809 wind turbine blade attached with EFP, the downstream velocity ratio decreases with increasing in angle of attack and the velocity deficit decrease with increasing turbulence intensity (TI) up to TI = 10%. The wake intensity for the S809 wind turbine blade and S809 airfoil with 10% of chord EFP performs the same for each downstream location.

Placing the wind turbine in the wind park next to another wind turbine poses a potential challenge for the park power performance. This research addresses the characteristics of the downstream turbulence intensity profile modified with the EFP in the wind turbine blade which improves the downstream characteristics of the turbine in the wind park.

The downstream velocity ratio decreases with increasing angle of attack and the velocity deficit decrease with increasing turbulence intensity (TI) up to TI = 10%.

The analysis of the effect of tool vibrations on the measured and simulated draught forces of cultivator tools. This paper aims to discuss this issue.

Soil bin measurements and discrete element method (DEM)-based simulations.

The soil-tool interaction induced free vibrations of cultivator tools have significant impact on the measured draught force, and the simulations made by using vibrating tools give similar results.

Accurate calibration of discrete element model parameters can be done based on the reproduction of the whole Mohr-Coulomb failure line. Draught force ratio – velocity ratio values seem to be independent of tool geometry and soil conditions in case of velocity ratio higher than 2.

DEM-based numerical simulations can be used for modeling the effect of tool vibration on the draught force values. During discrete element simulations of soil-tool interaction, the effect of tool vibration may not be neglected.

The paper demonstrates that during the discrete element modelling of the soil-tool interaction, the tool vibration phenomenon should not be neglected.

This paper aims to provide a detailed study on the influence of slip flow and thermal jump over mixed convection flow along an exponentially stretching surface. Also, impacts of suction/blowing, volumetric heat source/sink and velocity ratio parameter will be studied in this analysis.

The modeled governing equations for the assumed problem are dimensional nonlinear partial differential equations in nature. To reduce these equations, non-similar transformations are used to get the dimensionless nonlinear partial differential equations. Then, quasi-linearization technique is used to linearize these non-dimensional nonlinear partial differential equations. Finally, an implicit finite difference scheme is used to discretize the resulting equations.

The physical explanations are provided for the variations of various non-dimensional governing parameters over the velocity and temperature profiles. Also, the effects of these dimensionless parameters on skin friction coefficient and heat transfer rate are scrutinized in a manner which highlights their physical interpretation. The detailed discussion exhibits the fact that the streamwise co-ordinate velocity ratio parameter, partial slip parameter and the thermal jump parameter have significant influence over the flow and thermal fields.

This work has not been reported in the literature to the authors’ best of knowledge.

Having taken up our position on the above definition of this fundamental point, which closes the long‐standing discussion between upholders of the airscrew and those of the reaction system (just as in earlier days the distinction between impulse and work closed the classic discussion between the followers of Leibnitz and Descartes), we must now admit, without going into details, that this supposed attainment of equal efficiencies cannot be considered easy, if even possible, for the normal speeds of flight. It must also be admitted that a power unit, consisting of engine, compressor and jet, is at first sight a unit more complex, heavier and more bulky than the ordinary engine‐airscrew unit which has now been reduced to a high degree of simplicity and neatness. There is no doubt at all that in the sphere of the sub‐acoustic velocities the airscrew will reign supreme.

The purpose of this paper is to present a computational fluid dynamic simulation for the investigation of the particles segregation phenomenon in the gas–solid fluidized beds.

These particles have the same size and different densities. The k–ε model and multiphase particle-in-cell method have been utilized for modeling the turbulent fluid flow and solid particles behaviors, respectively. The coupled equations of the velocity and pressure have been solved by using a combination of SIMPLE and PISO algorithms. After validating the simulation, different mixing indices, with different calculation bases, have been investigated, and it has been found that the Lacey mixing index, which was defined based on statistical concepts, is suitable to investigate the segregation/mixing phenomena of this bed in different conditions. Finally, the effects of parameters such as velocity, particle density ratio, jetsam concentration, and initial arrangement on the segregation/mixing behaviors of the bed have been studied.

The results show that the increase in the superficial gas velocity decreases the mixing index to a minimum value and then increases this index in the beds with mixed initial condition, unlike the beds with separated initial condition. Moreover, an increase in the particle density ratio increases the minimum fluidization velocity of the bed, and also the amount of segregation, and increase in the jetsam concentration increases the value of the mixing index.

A computational fluid dynamics simulation has been presented for the particles segregation phenomenon in the gas–solid fluidized beds.