EFFECTS OF THERMAL RADIATION AND BUOYANCY FORCE ON TRANSIENT HARTMANN FLOW IN A CHANNEL WITH PERMEABLE WALLS

The combined effects of thermal radiation, buoyancy force and variable heat source on an unsteady MHD flow of a conducting fluid through a porous walled channel is theoretically investigated. Base on some simplified assumptions, the model partial differential equations are obtained and tackled analytically using variable separable technique. Numerical solutions depicting the impact of various embedded thermophysical parameters on the fluid velocity and temperature profiles, skin friction and Nusselt number are displayed graphically and quantitatively discussed. An escalation in both skin friction and heat transfer rate is observed with a rise in fluid injection–suction at the channel walls.

Wavy Walls, a Passive Way to Control the Transition to Turbulence. Detailed Simulation and Physical Explanation

Inducing spanwise motions in the vicinity of solid boundaries alters the energy, mass and/or momentum transfer. Under some conditions, these motions are such that drag is reduced and/or transition to turbulence is delayed. There are several possibilities to induce those spanwise motions, be it through active imposition a predefined velocity distribution at the walls or by careful design of the wall shape, which corresponds to passive control.In this contribution, we investigate the effect that wavy walls might have on delaying transition to turbulence. Direct Numerical Simulation of both planar and wavy-walled channel flows at laminar and turbulent regimes are conducted. A pseudo laminar regime that remains stable until a Reynolds number 20% higher that the critical is found for the wavy-walled simulations. Dynamic Mode Decomposition applied to the simulation data reveals that in these configurations, modes with wavelength and frequency compatible with the surface undulation pattern appear. We explain and visualize the appearance of these modes. At higher Reynolds numbers we show that these modes remain present but are not dominant anymore. This work is an initial demonstration that flow control strategies that trigger underlying stable modes can keep or conduct the flow to new configurations more stable than the original one.

Experimental Optical Testing and Numerical Verification by CuFSM of Compression Columns with Modified Channel Sections

Thin-walled channel columns with non-standard cross-section shapes loaded with gradually increasing compressive force applied at the geometric centre of gravity of the cross-section were the subject of the investigations presented in this paper. The aim of the research was to determine which of the columns has the most favourable geometrical characteristics in terms of the applied load. The main investigation was an experimental study carried out using two methods: strain gauging and the optical method. Based on strain gauging, the critical forces were determined using the strain averaging method and the linear regression tangent to compression plot method. In addition, modern optical tests were performed using the ARAMIS system. The buckling forces at which the first signs of buckling appear and the buckling modes of columns were determined. The results obtained from the experimental tests were used to validate the results of numerical tests carried out using the Finite Strip Method (CuFSM). Based on this method, the values of critical forces and the percentage contribution of individual buckling forms to the loss of stability of the compressed columns were determined.

The research of the processes of formation of porous non-ferrous metals

Foamed metals are promising materials with a unique combination of mechanical and operational properties: low specific gravity, low thermal conductivity, ability to absorb acoustic and electromagnetic vibrations, and the ability to deform under a constant load. Currently, the most used methods for producing foamed aluminum and foamed magnesium are methods based on mixing gas or porophore into molten aluminum and forming a porous structure during the solidification of the aluminum melt. An alternative to this technology is the formation of a porous structure through the use of soluble granules that pre-fill the mold and after impregnating the granules with molten metal and solidifying the castings, they are leached. The work aims to determine the influence of casting modes and the size of granules on the depth of impregnation of granular filling with metal melt during the formation of porous aluminum castings. The authors proposed the technique for calculating the depth of impregnation of granular filling when producing castings of porous non-ferrous metals based on the calculation of melt cooling when moving along the thin-walled channel. The calculations made it possible to determine the depth of impregnation and establish the allowable wall thickness of the casting of porous aluminum, depending on the size of the granules used, the speed of the melt in a form, the mold temperature, and the temperature of molten aluminum. The study identified that to increase the depth of impregnation and obtain porous aluminum castings with thinner walls, it is advisable to increase the diameter of the salt granules and not the temperature and hydrodynamic modes of casting. The authors carried out calculations and identified the influence of the casting regimes and the diameter of the granules on the depth of mold impregnation to obtain porous castings from promising magnesium alloys.

Multi-Mode Buckling Analysis of FGM Channel Section Beams

The interactive buckling phenomenon in thin-walled channel section beams is investigated in this paper. This study deals with medium length beams made of the step-variable functionally graded materials (FGM) which consists of aluminum and titanium layers. The interaction of local, primary and secondary global buckling mode and their effect on the load-carrying capacity is discussed. The parametric studies are performed to assess the effect of the thickness of the beam’s component, its length and position of the individual layer on the equilibrium paths. Additionally, the influence of the adhesive layer between materials was analyzed. The problem was solved using the Finite Element Method.