In the present paper, we investigate the hydrodynamic instability of Dean flow under different Dean numbers ranging from 1 to 2500, curvature ratios from 0.0001 up to 1000 and temperatures ranging from 273.15 K to 373.15 K. To study of fluid flow instability, analytical velocity profiles under intended conditions and energy gradient function K in the energy gradient method are evaluated. The results of present study show that, as the curvature ratio increases the flow becomes more stable. Moreover, no regular and significant effects on the energy gradient function K were achieved by increasing of temperatures. We found that, the origin of instability in the entire flow field is located on the inner wall of the parallel curved walls, especially for larger curvature ratios. We also reported the critical value of the energy gradient function K for the onset of instability corresponding to the critical Dean number.

In the present paper, we analyzed the effects of magnetic field on the three dimensional flow of a nanofluid having the suspension of ferrous nano-particles within the framework of a non-uniformly thicked sheet in a slip flow regime. The sheet of variable thickness is assumed to be stretched in horizontal and transverse directions. The effects of thermophoretic forces and Brownian motion have also been incorporated into the governing equations. The RK-Fehlberg-integration scheme with shooting technique is employed to resolve the altered governing non-linear differential equations. Velocity, temperature and concentration profiles are presented and discussed for two cases namely uniform thickness stretching sheet UTSS (n = 1) and variable thickness stretching sheet VTSS (n ≠ 1), and skin friction coefficient, reduced Nusselt number and Sherwood number are computed and analyzed through tables. The results reveal that heat and mass transfer processes over slendering sheet matches with those over a flat sheet in the presence of slip flow regime.

Free convective flow and heat transfer of nanofluid close to the inclined plate immersed in the porous medium under the effects of uniform magnetic field and solar radiation has been studied. Boundary-layer approach, Boussinesq approximation and two-phase nanofluid model have been used for a formulation of the governing equations taking into account convective-radiative heat exchange with an environment. The local similarity method has been adopted for the analysis of the considered phenomenon. The obtained equations have been solved numerically using MATLAB software. The effects of control characteristics on profiles of velocity, temperature and nanoparticles volume fraction as well as Nusselt number have been studied in detail.

Effects of geometric parameters of diffuser vanes as well as impeller micro grooves depth on the performance of a vertically suspended centrifugal pump have been studied. Different diffuser vanes height,leading angles, trailing angles, wrapping angles and furthermore, impeller micro grooves depths have been analyzed thoroughly. Numerical results have been verified by comparing experimental data. Results, without considering cavitation, reveal that diffuser vanes height has the profound impact on the vertically suspended centrifugal pump performance followed by vanes wrapping angle. Additionally, it is observed that delivered head and efficiency of micro-grooved impellers reduce more by flow rate enhancing rather than that of the original impeller.

The shapes of a pore resulting from an entrapped bubble by a solidification front for different locations of the bubble below the free surface are predicted in this work. Bubble location is an important factor affecting temperature gradient in liquid, solute gas dissipated into the ambient, heterogeneous nucleation of the bubble and shape of the bubble cap, and subsequent entrapment and the pore shape in solid. The shapes of pores in solid influence not only material properties, but also contemporary issues of engineering, biology, medical technology and science, etc. This study takes into account solute transport across a coupling shape of the pore cap determined by the Young-Laplace equation governing balance of liquid, gas and capillary pressures. The results find that increases in depthwise location of a bubble increase pore radius and time for bubble entrapment as solute transport is from the pore across cap emerged through a concentration boundary layer along the solidification front into surrounding liquid in the early stage. On the other hand, the bubble cannot be entrapped, provided that solute transport in opposite directions across the cap submerged in a concentration boundary layer along the solidification front. The predicted growth and entrapment of a tiny bubble as a pore in solid agree with experimental data. Understanding and controlling of the pore shape via controlling bubble location is of interest and challenging.

An underwater shock loading experimental device is used to simulate underwater explosion shock waves. The aim of this study is to investigate the influence of flyer momentum on the response of an aluminium plate to this underwater shock loading experimental device. The simulation accuracy can be verified by comparing theoretical data with the simulation and experimental results. Through simulations, an aluminium plate’s deformation and pressure specific impulse can be determined when flyers impact the piston at different velocities but at the same momentum. The aluminium plate's deformation and pressure specific impulse are constant when the flyers had constant momentum because both are directly proportional to the flyer momentum. The results have an important practical value for understanding and using this type of experimental device.

In the current study, for the first time, a semi-analytical technique is used for solving eigenvalue problem arising from linear hydrodynamics stability of fluid flow through the curved rectangular ducts at different curvature ratios and aspect ratios. To this accomplishment, symmetric disturbances are assumed and the Homotopy perturbation method (HPM) is applied to solve our eigenvalue problem for curvature ratios ranging from 0.01 to 0.8 and aspect ratios ranging from 0.05 to 20. Our semi-analytical results are validated through the existing numerical and experimental data, showing good agreement. The semi-analytical results indicate that, as the curvature ratio increases the critical Dean number (Dnc) is increased and the flow becomes more stable, especially for aspect ratios lower than 1.Moreover, for all intended curvature ratios, irregular behavior in variation of Dnc is detected by an increase in the aspect ratio. So that, the Dnc is decreased when the aspect ratio increases from 0.05 up to 1 and the fluid flow becomes unstable. When the aspect ratio is increased from 1 to 5, it causes to increase the Dnc and fluid flow becomes stable. Furthermore, when the aspect ratio increases from 5 to 20, the Dnc is decreased again. In addition, Dnc and eigenvalues of critical complex wave number corresponding to Dnc for the onset of Dean flow instability is reported under different curvature ratios and aspect ratios.

In this article, random flutter of multi-stable airfoils in steady flow is investigated by means of the analytical method for stochastic P-bifurcation, where the effect of the stochastic disturbance in the generalized flow speed on the airfoils is considered. The results show that under constant stochastic disturbance intensity, the coherence resonance could be induced by the variation of generalized flow speed. In addition, if the generalized flow speed keeps unchanged and its stochastic disturbance is sufficiently large, the response of the system will tend to be a stable equilibrium. It indicates that the parametric stochastic disturbance is effective to maintain system stability. Moreover, it is shown in this paper that the analytical method for stochastic P-bifurcation can be extended to study stochastic P-bifurcations in other high-dimensional systems.

The general form of mathematical model of cable winding/unwinding system is defined for several different constructions. The novelty of this mathematical model is detection and mathematical formulation of influence of new dynamic variables: winding/unwinding radius and cable length on dynamic response of cable winding/unwinding system. The validity of the obtained theoretical contribution has been illustrated through one case study by using a newly developed software package CWUSOFT which was generated in MATLAB. Theoretical and simulation results are confirmed through the experimental analysis of one novel construction of the cable winding/unwinding system.

This study aims at improving the performance of a centrifugal pump by using different angular diffusers on the downstream side of the centrifugal pump impeller. Numerical and experimental studies have been carried out on different vaned and non-vaned diffuser with three different wall divergence angle (α) of 0°, 5° and 10° to achieve that purpose. The data analyses show good agreement between the numerical and experimental results. They reveal profound effect of the divergence angle (α) of angular vaned diffuser on the head and overall efficiency of centrifugal pumps especially at high flow rates as they broaden operating region of the centrifugal pump. In fact it is found that the head and overall efficiency of impeller with vaned diffuser α = 10° enhance by 15.4 and 9 percent respectively compared to that of centrifugal pump with no vaned diffuser at high flow rates. Furthermore the head and overall efficiency of impeller with vaned diffuser α = 10° increase by 5.7 and 7 percent respectively in comparison with the impeller with vaned diffuser α = 0°.

This study investigates the effect of bracket bonding-debonding on the tribological properties of human tooth enamel, when two different adhesives are applied. The nano-scratch experiment was performed on the enamel at untreated and under the bracket regions to obtain wear resistance, scratch hardness and friction coefficient. The results indicated that the tribological properties of the enamel vary significantly after bracket bonding-debonding. However, no significant difference exists between the effects of bracket bonding by the nano-composite and the composite adhesives on the tribological properties. Therefore, considering the mechanical and physical properties of the nano-composite adhesive, its bond strength for orthodontic bracket bonding and the influences on the enamel after removing the bracket, the use of nano-composite adhesive is suitable for orthodontic treatments.

In this study, the pull-in phenomenon of a Nano-actuator is investigated employing a nonlocal Bernoulli-Euler beam model with clamped-clamped conditions. The model accounts for viscous damping, residual stresses, the van der Waals (vdW) force and electrostatic forces with nonlocal effects. The hybrid differential transformation/finite difference method (HDTFDM) is used to analyze the nonlocal effects on a graphene sheet nanobeam, which is electrostatically actuated under the influence of the coupling effect, the von Kármán nonlinear strains and the fringing field effect. The pull-in voltage as calculated by the presented model deviates by no more than 0.29% from previous literature, verifying the validity of the HDTFDM. Furthermore, the nonlocal nonlinear behavior of the electrostatically actuated nanobeam is investigated, and the effects of viscous damping, residual stresses, and length-gap ratio are examined in detail. Overall, the results reveal that small scale effects significantly influence the characteristics of the graphene sheet nanobeam actuator.

This study investigates numerically the performance of applying aerospike nozzle in a hydrogen peroxide mono-propellant propulsion system. A set of governing equations, including continuity, momentum, energy and species conservation equations with extended k-ε turbulence equations, are solved using the finite-volume method. The hydrogen peroxide mono-propellant is assumed to be fully decomposed into water vapor and oxygen after flowing through a catalyst bed before entering the nozzle. The aerospike nozzle is expected to have high performance even in deep throttling cases due to its self-compensating characteristics in a wide range of ambient pressure environments. The results show that the thrust coefficient efficiency (Cf,η) of this work exceeds 90% of the theoretical value with a nozzle pressure ratio (PR) in the range of 20 ~ 45. Many complex gas dynamics phenomena in the aerospike nozzle are found and explained in the paper. In addition, performance of the aerospike nozzle is compared with that of the bell-shape nozzle.