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This article examines the influence of centrifugal buoyancy on the hydrodynamic and thermal behaviour in fully developed flow through an orthogonally rotating duct of aspect ratio 2:1. A series of computations have been performed at rotation numbers ranging from 0 to 0.2, for constant‐density flows (no buoyancy) and also for different levels of outward and inward buoyancy. The resulting comparisons reveal that for a Reynolds number of 32,500, rotational buoyancy effects become significant at Rayleigh number values greater than 107. In outward flows, buoyancy is found to strengthen the effects of the Coriolis force on the mean motion and, by raising turbulence levels, buoyancy also enhances wall heat transfer along both the pressure and the suction side of the rotating duct. In inward flows, it is found that strong buoyancy can reverse the direction of the Coriolis‐induced secondary motion, which causes a strong rise in wall heat transfer along the suction side and a similarly significant fall in heat transfer along the pressure side. The computed effects on heat transfer are in qualitative agreement with the findings of a number of experimental studies. For both inward and outward flows, at a constant Reynolds number, the modifications of centrifugal buoyancy on the side‐averaged levels of heat transfer correlate reasonably well with the rotational Rayleigh number.

Legged vehicles offer several advantages over wheeled vehicles, particularly on broken terrain, but are presently too slow to be considered for many high‐speed tasks. This paper presents an effective 3D controller for a high‐speed quadruped trot.

To successfully regulate forward velocity and heading, secondary motions such as body pitch and roll must be stabilised. The complicated coupling between pitch and roll motion causes the control effort on one axis to disturb the motion and control effort of the other. Unlike the modular methods in previous research, the algorithm presented here employs a cooperative approach where pitch stability effort is directly accounted for by the roll controller.

When the secondary motions such as pitch and roll are well stabilized, forward velocity and heading can be regulated up to 3 m/s and 20°/s, respectively.

For many quadrupeds, trotting is usually employed as the precursor to galloping, which is ultimately used at top speeds. Because these two gaits are commonly used together, we expect their control algorithms to share a number of similar components. It is then expected that understanding the quadruped trot will serve as a valuable foundation to understanding the quadruped gallop.

This appears to be the first reported regulation of quadruped heading while running at significant speeds.

The purpose of this paper is to present, for the first time, a mathematical model for a piston skirt in mixed lubrication with respect to applying a smart fluid in lubrication. In this way, the smart fluid, as a lubricant with controlled variable viscosity, is proposed and applied to minimize the power loss in the interaction between liner and skirt.

Based on signal processing, the relationships between viscosity of lubricant and the friction loss, the hydrodynamic and contact friction force consequently are found, as part of an effective approach to acquire the function of variable viscosity.

It is shown that hydrodynamics and contact friction forces can be controlled and minimized by using the variable viscosity signal with the optimized viscosity signal technique.

In this paper, a mathematical model for a piston skirt in mixed lubrication with respect to applying a smart fluid in lubrication is presented for the first time.

This paper aims to study the fluid flow and heat transfer through a spiral double-pipe heat exchanger. Nowadays using spiral double-pipe heat exchangers has become popular in different industrial segments due to its complex and spiral structure, which causes an enhancement in heat transfer.

In these heat exchangers, by converting the fluid motion to the secondary motion, the heat transfer coefficient is greater than that of the straight double-pipe heat exchangers and cause increased heat transfer between fluids.

The present study, by using the Fluent software and nanofluid heat transfer simulation in a spiral double-tube heat exchanger, investigates the effects of operating parameters including fluid inlet velocity, volume fraction of nanoparticles, type of nanoparticles and fluid inlet temperature on heat transfer efficiency.

After presenting the results derived from the fluid numerical simulation and finding the optimal performance conditions using a genetic algorithm, it was found that water–Al₂O₃ and water–SiO₂ nanofluids are the best choices for the Reynolds numbers ranging from 10,551 to 17,220 and 17,220 to 31,910, respectively.

The purpose of this study is to investigate the effects of the axial piston pin motion on the tribological performances of the piston skirt and cylinder liner vibration for an internal combustion engine (ICE) under different operation conditions.

The dynamic equation for the piston incorporating into axial piston pin motion is derived first. Then, the proposed equation and associated lubrication equations are solved using the Broyden algorithm and difference method, respectively. Moreover, the axial motion of the piston pin and its slap on the cylinder liner are studied under different operation conditions.

The axial piston pin motion leads to an overall increase in the friction power consumption. Increments in the ICE speed and lubricant viscosity can augment the axial pin motion and cylinder liner vibration, especially in the power stroke. The said increments cause the instability of the piston motion in the cylinder. The axial motion of piston pin can be restrained through the eccentricity of the piston pin close to the thrust side of the cylinder liner.

This study conducts detailed discussions of the effect of axial piston pin motion on tribological and dynamic performances for piston skirt-cylinder liner system of an internal combustion engine and gives a helpful reference to analyses and designs of internal combustion engines.

This paper aims to compute flow and heat transfer through a straight, orthogonally rotating duct, with ribs along the leading and trailing walls, in a staggered arrangement and at an angle of 45° to the main flow direction.

Flow computations have been produced using a 3D non‐orthogonal flow solver, with two two‐layer models of turbulence (an effective‐viscosity model and a second‐moment closure), in which across the near‐wall regions the dissipation rate of turbulence is obtained from the wall distance. Flow comparisons have been carried out for a Reynolds number of 100,000 and for rotation numbers of 0 (stationary) and 0.1. Temperature comparisons have been obtained for a Reynolds number of 36,000, a Prandtl number of 5.9 (water) and rotation numbers of 0 and 0.2 and also at a Prandtl number of 0.7 (air) and a rotation number of 0.

It was found that both two‐layer models returned similar flow and thermal predictions which are also in close agreement with the flow and thermal measurements. The flow and thermal developments are found to be dominated by the rib‐induced secondary motion, which leads to strong span‐wise variations in the mean flow and the local Nusselt number and to a uniform distribution of turbulence intensities across the duct. Rotation causes the development of stronger secondary motion along the pressure side of the duct and also the transfer of the faster fluid to this side. The thermal predictions, especially those of the second‐moment closure, reproduce the levels and most of the local features of the measured Nusselt number, but over the second half of the rib interval over‐predict the local Nusselt number.

The work contributes to the understanding of the flow and thermal development in cooling passages of gas turbine blades, and to the validation of turbulence models that can be used for their prediction, at both effective viscosity and second‐moment closure levels.

The results from a direct numerical simulation (DNS) of turbulent, incompressible flow through a square duct, with an imposed temperature difference between the horizontal walls, are presented. The vertical walls are assumed perfectly insulated, and the Reynolds number, based on the bulk velocity and the hydraulic diameter, is about 4400. Our results indicate that secondary motions do not affect dramatically global parameters, like the friction factor and the Nusselt number, with respect to the plane‐channel flow, but the distributions of the local shear stress and heat flux at the walls are highly non‐uniform, due to the presence of these secondary motions. It is also shown that an eddy‐diffusivity approach is capable to reproduce well the turbulent heat flux. All simulations were performed by an efficient finite volume algorithm. A description of the numerical algorithm, together with an analysis of time‐accuracy, is included. The OpenMP parallel programming language was exploited to obtain a moderately‐scalable application.

The present work aims to deal with simulation of turbulent duct flow using generalized lattice Boltzmann equation (GLBE) in which large eddy simulation was employed.

The sub-grid scale turbulence effects were simulated through a shear-improved Smagorinsky model (SISM) which is capable of predicting turbulent near wall region accurately without any wall function. Computations were done for fully developed turbulent square duct flow at Ret=300, based on duct width and average friction velocity.

Results obtained for turbulent duct flow reveal that the GLBE in conjunction with SISM is able to correctly predict the existence of secondary flows and the computed detailed structure of first- and second-order statistics of main and secondary motions. The methodology is validated by comparing with previously published data. It is concluded that such framework is capable of predicting accurate results for turbulent duct flow. In addition, the operations in the present method are local; it can be easily programmed for parallel machines.

The numerical method, including generalized lattice Boltzmann method with forcing term and implementation of SISM in GLBE, is used for the first time to simulate turbulent duct flow.

The present investigation is an extension of the authors’ previous work on ducts with different cross sections. It concerns application of turbulence models for forced convective heat transfer in three‐dimensional corrugated or wavy ducts. Different wavy ducts with fully developed flow and temperature fields are considered. The numerical approach is based on the finite volume technique with a non‐staggered grid arrangement. For handling the pressure‐velocity coupling the SIMPLEC‐algorithm is used. Cyclic boundary conditions are imposed in the main flow direction to achieve fully developed conditions. The non‐linear k‐ε model of Speziale with wall functions is used to calculate the turbulent stresses. The simple eddy diffusivity concept is applied to calculate the heat fluxes, but the GGDH and the WET methods are also used in some cases. The influence of the geometry parameters and comparison between different ducts are presented in terms of the friction factor and average Nusselt number. In particular the secondary velocity field and the cross sectional temperature distributions are investigated.

The purpose of this paper is to present an analytical study on an unsteady magnetohydrodynamic (MHD) boundary layer flow of a rotating viscoelastic fluid over an infinite vertical porous plate embedded in a uniform porous medium with oscillating free-stream taking Hall and ion-slip currents into account. The unsteady MHD flow in the rotating fluid system is generated due to the buoyancy forces arising from temperature and concentration differences in the field of gravity and oscillatory movement of the free-stream.

The resulting partial differential equations governing the fluid motion are solved analytically using the regular perturbation method by assuming a very small viscoelastic parameter. In order to note the influences of various system parameters and to discuss the important flow features, the numerical results for fluid velocity, temperature and species concentration are computed and depicted graphically vs boundary layer parameter whereas skin friction, Nusselt number and Sherwood number at the plate are computed and presented in tabular form.

An interesting observation is recorded that there occurs a reversal flow in the secondary flow direction due to the movement of the free stream. It is also noted that a decrease in the suction parameter gives a rise in momentum, thermal and concentration boundary layer thicknesses.

Very little research work is reported in the literature on non-Newtonian fluid dynamics where unsteady flow in the system arises due to time-dependent movement of the plate. The motive of the present analytical study is to analyse the influences of Hall and ion-slip currents on unsteady MHD natural convection flow of a rotating viscoelastic fluid (non-Newtonian fluid) over an infinite vertical porous plate embedded in a uniform porous medium with oscillating free-stream.