International Journal of Theoretical and Applied Multiscale Mechanics (6 papers in press)
A CFD Investigation of Nozzle Position Effect and Turbulent Flow Phenomena of a Hyperloop Model
by Steven Goddard, Yufeng Yao
Abstract: This investigation analyses a conceptual Hyperloop model in a low-pressure tube using CFD simulation technique. A precursor validation study, similar to a published work, is adopted, and used as a baseline model to develop a replication of Hyperloop configuration. The study continues with 2D simulations of three rear nozzle positions to identify a low-drag configuration, steady 3D simulations to capture more complex mean flow features, and unsteady 3D simulation to analyse time-dependant flow characteristics. It was found that the lower the rear nozzle position, the better the drag reduction, with an optimal slope angle of 8
Keywords: Hyperloop concept; Vacuum tube transport; Low Pressure condition CFD modelling; Rear nozzle position; High-speed turbulent flow.
Jenkins model based ferrofluid lubrication of a squeeze film in rough curved circular plates considering slip velocity
by Jimit R. Patel, G.M. Deheri
Abstract: An attempt has been made to study and analyse the combined effect of roughness and slip velocity on the performance of a Jenkins model based magnetic squeeze film in curved rough circular plates taking velocity slip into account. The curvatures of both the plates are described by exponential functions. The stochastic model of Christensen and Tonder has been used to evaluate the effect of surface roughness. The associated stochastically averaged Reynolds type equation has been solved to obtain the pressure distribution leading to the computation of load carrying capacity. The graphical representations of the solution reveal that although Jenkins model modifies the performance as compared to Neuringer-Rosensweig model, the magnetisation may not go too far in reducing the adverse effect of slip velocity and standard deviation associated with roughness because the material constant parameter brings down the load carrying capacity. However, the situation is fairly improved in the case of negatively skewed roughness particularly, when variance (-ve) is involved. This article also ensures that by keeping the slip parameter at minimum and choosing the curvature parameters the magnetic fluid lubrication may lead to an augmented performance.
Keywords: curved circular plates; roughness; Jenkins model; magnetic fluid; slip velocity.
Determination of interfacial fracture energy for 'pop-in' delaminations in a glass-epoxy system using the indentation method
by Karen Hutchins, Thomas Buchheit, Rajan Tandon, Tariq Khraishi
Abstract: The adhesion of coatings often controls the performance of the substrate-coating system. Certain engineering applications require an epoxy coating on a brittle substrate to protect and improve the performance of the substrate. Interfacial adhesion measurements of such systems provide a quantitative metric of that performance. Indentation experiments were performed to induce interfacial delaminations in a glass substrate-epoxy coating system. Delamination loads and radii were measured and applied to an analytical solution originally developed by Rosenfeld et al. (1990) to estimate the interfacial fracture energy of the substrate-coating adhesive bond. Results suggest an interfacial bond strength far exceeding that of similar previously studied glass-epoxy systems.
Keywords: indentation; adhesion; bonding; interfaces; coatings; epoxy; glass; fracture energy.
Micromorphic elasticity for an axisymetrically loaded cylindrical thick-walled structure under plane strain conditions
by Koffi Enakoutsa
Abstract: In this paper we derive a closed-form solution for the problem of a second gradient elastic circular thick-walled cylinder subjected to some axisymmetric loading conditions and deformed in plane strain. The second gradient elastic model used is the one of Gologanu, Leblond, Perrin and Devaux proposed some years ago and used in the context of the numerical implementation of a micromorphic model for ductile fracture in porous plastic metals. The ordinary Cauchy stress and 'hyperstress' tensors are computed as a function of the displacement field which is obtained via a suitable combination of the balance equations, compatibility, stress-strain/hyperstress-gradient of the strain relationships, and appropriate boundary conditions. The first gradient solution is recovered when the second gradient effects are negligible. This study demonstrates that the first gradient elastic solution may not be accurate, particularly in elastic materials exhibiting substantial microstructure dependence. Future works will use the newly derived solution to interpret the size effects experimentally observed, for instance, in pressurised sandstone hollow cylinders.
Keywords: thick-walled cylinder; strain gradient elasticity; closed-form solution; axisymmetric load.
Large-scale flow structures in turbulence mixing of sonic jet injection into supersonic crossflow
by El-Hadi Khali, Yufeng Yao
Abstract: A hybrid Reynolds-averaged Navier-Stokes (RANS) and large-eddy simulation (LES) fluid dynamics simulation has been performed to explore physical insights of flow mixing characteristics, resulted from an interaction between a sonic jet issuing perpendicularly into a supersonic crossflow. This numerical approach allows for the simulations to resolve unsteady large-scale flow structures, and as well as to capture the mean flow accurately, both parameters play important roles in this kind of flow mixing process. After validating time-averaged 'mean' results against available experimental measurements, further comparison of instantaneous unsteady flow field is made to reveal dynamic process occurred in the mixing flow computation. Some key flow characteristics observed in the experiments are successfully reproduced by present numerical study, namely boundary layer flow separation at the jet exit and shear-layer vortex development along the interface between the jet stream and the crossflow, the latter is mainly due to the Kelvin-Helmholtz instability.
Keywords: coherent structures; sonic jet in supersonic crossflow; counter rotating vortex pair; CRVP; improved-delayed detached-eddy simulation; IDDES; bounded central differencing scheme; implicit time integration.
Experimental study on heat transfer enhancement ability of water-based graphene oxide nanofluid
by Hao Su, Xin-Yi Yu, Minzhong Gao, Yi-Ran Mo, Yi Zhang, Fei Xing, Aicheng Li
Abstract: Thermal properties of water-based nanofluid with different mass fraction of the graphene oxide nanosheets, and convective heat transfer capability in the microchannel heat exchangers at different temperature conditions are studied experimentally. Experimental results show that the nanofluid can be stable under 60°C, but it would precipitate after four hours heating at 99°C. The kinematic viscosity decreases with extent of 50%~60% as the temperature of nanofluid increases from 10°C to 45°C and the thermal conductivity arises by 17.54%. The heat transfer experiments show that convective heat transfer capacity of water-based graphene oxide nanofluid is better than water when the wall temperature is below 100°C. When the wall temperature of microchannel heat exchangers is above 100°C, the graphene oxide nanosheets would precipitate which leads to the deterioration of convective heat transfer capacity.
Keywords: graphene oxide; nanofluid; thermal properties; heat transfer enhancement; thermal conductivity.