Numerical investigation of swirl flow inside a supersonic nozzle

This study reports the Computational Fluid Dynamics (CFD) results of a swirling flow induced by introducing a helical insert inside a supersonic nozzle. The CFD simulation shows a very complex unsteady, non-axisymmetric flow pattern for the swirl flow inside the nozzle.The flow is investigated by solving the Reynolds averaged Navier Stokes (RANS) equations with k- and Reynolds Stress Model (RSM) turbulence models to predict the flow patterns and the type of swirling flow. Computations are conducted for a range of nozzle pressure ratios with and without swirl inside the converging–diverging nozzle. The study has revealed a new understanding and data for flow features such as shock location, mass flow rate and anisotropic turbulence

Optimization of partially textured parallel thrust bearings with square-shaped micro-dimples

In this study we attempt to find the optimum geometrical parameters of square-shape micro-dimples imposed on parallel flat bearing surfaces which give the best tribological performance, including load capacity and friction coefficient. An analytical solution of Reynolds equation for the surfaces involving numerous dimples is presented, then considering the variations of number of dimples as well as dimple length and height ratios for a constant dimpled length, it is tended to get the optimum value of parameters. It is shown that despite the variations of different studied geometrical parameters, it seems the optimum value of these parameters remain nearly constant

Optimised textured surfaces with application in piston-ring/cylinder liner contact

The application of textured surfaces in tribology has recently gained a huge momentum. In this chapter, a systematic approach to investigate the maximum outcomes from employing such surfaces is introduced with an insight into their application in internal combustion engines. A combination of various affecting parameters on the tribological performance of such surfaces is studied and the optimum results are introduced. The effect of employing such optimised textures in enhancing the lubrication condition in piston ring/cylinder liner contact is also studied

Analytical analysis and optimisation of the Rayleigh step slider bearing

In tribology, the Rayleigh step is known as a bearing with the highest load capacity amongst all other possible bearing geometries. In classical resources on tribology, it is also shown that there is an optimum geometry for the Rayleigh step providing the highest load capacity. However, the analyses are confined to a special case where the effect of hydrostatic pressure is neglected. Furthermore, the possible optimum parameters in terms of the friction force and/or friction coefficient as well as the lubricant flow rate have not been discussed. In this study, the Rayleigh step is comprehensively analysed including the effect of variations of pressure at the boundaries on the optimum parameters. In addition, the bearing is also optimised considering lubricant flow rate, friction force and friction coefficient. It is shown that the optimum bearing parameters are strictly dependent on the variations of the pressure at the boundaries. It is also verified that the optimum point(s) in terms of load capacity are not necessarily equal to the optimum point(s) considering friction coefficient and/or lubricant flow rate even though if there is no pressure difference between bearing endings

Spreadsheet tools to estimate the thermal transmittance and thermal conductivities of gas spaces of an Insulated Glazing Unit

An Insulated Glazing unit (IGU) is constructed with two or more layers of glass panes sealed together by gas spaces in-between. IGUs are prevalent in windows, doors and rooflights, primarily due to their improved thermal resistance. Today, most IGUs are either two or three layered. Adding further layers of glass improves thermal insulation but with the penalty of increased cost and weight. Low emissivity (Low-e) film coatings, when deposited on the glass panes, reduce long-wavelength radiative heat losses. Furthermore, filling the gas spaces with the inert gases (e.g. Argon, Krypton, Xenon and SF6), further reduce conduction and natural convection across the gap. In summary, higher thermal insulation performance of an IGU can be achieved with gas fillings and Low-e coatings on glass. This report discusses spreadsheets that have been developed, capable of estimating the thermal transmittance values of IGU, as per BS EN 673. The spreadsheet tools also have the ability to estimate the thermal conductivity of the gas spaces between the panes of IGU

IJTC2006-12167 OPTIMIZATION OF PARTIALLY TEXTURED PARALLEL THRUST BEARINGS WITH SQUARE- SHAPED MICRO-DIMPLES

ABSTRACT In this study we attempt to find optimum geometrical parameters of square-shape micro-dimples imposed on parallel flat bearing surfaces which give the best tribological performance, including load capacity and friction coefficient. An analytical solution of Reynolds equation for the surfaces involving numerous dimples is presented, then considering the variations of number of dimples as well as dimple length and height ratios for a constant dimpled area, it is tended to get the optimum value of parameters. It is shown that despite the variations of different studied geometrical parameters, it seems the optimum value of these parameters remain nearly constant. Keyword

Design, development and numerical analysis of honeycomb core with variable crushing strength

A honeycomb core with half-circular cut-away sections at the spine (the adjoining cell walls) is designed and developed and numerically tested under axial dynamic load condition. The parametric study is invoked to identify the effect of various circular cut-away dimensions. In one embodiment a half-circular shaped cuts are removed from the top of the cell where the cell is impacted and its radius decreases toward the trailing edge of the cell. Numerical (FE) analysis was performed using explicit ANSYS/LS-DYNA and LS-DYNA codes to investigate the crushing performance, where impact angles 30° and 90° was combined with velocity of 5:3 m/sec. The crushing strength and internal energy absorption of the modified honeycomb cores with cut-away sections are then monitored to define the design parameters. The representative Y-section (axisymmetric model) is used for numerical analysis which simulates the honeycomb crushing performance. The numerical results of these innovative models show cyclic buckling effect in which crushing strength increases linearly as the rigid wall passes through. The FE results are validated with corresponding published experiments of the original unmodified honeycomb core (without cut-away)

An analytical approach for analysis and optimisation of slider bearings with infinite width parallel textures

This paper introduces an analytical approach to study the textured surfaces in hydrodynamic lubrication regime. For this purpose, a method of integrating the Reynolds equation for slider bearings with surface discontinuities is presented. By introducing appropriate dimensionless parameters, analytical relations for various texture profiles in both indented and projected forms are delivered. These relations express the nature of mathematical dependence between textured bearing performance measures and geometrical/operational parameters. An optimisation procedure is employed to achieve the optimum texturing parameters promoting maximum load capacity, load capacity to lubricant flow rate ratio and minimum friction coefficient for asymmetric partially textured slider bearings

Verification of calculation code THERM in accordance with BS EN ISO 10077-2

Calculation codes are useful in predicting the heat transfer features in the fenestration industry. THERM is a finite element analysis based code, which can be used to compute thermal transmittance of windows, doors and shutters. It is important to verify results of THERM as per BS EN ISO 10077-2 to meet the compliance requirements. In this report, two-dimensional thermal conductance parameters were computed. Three versions of THERM, 5.2, 6.3 and 7.1, were used at two successive finite element mesh densities to assess their comparability. The results were all compliant with the aforementioned British Standard

Verification of finite element analysis code CalculiX CrunchiX (ccx) in accordance with ISO 10211:2007

The design standard ISO 10211 provides four thermal problems; a square column, a composite structure, a multi-environment building envelope and an iron bar penetrating an insulation layer. Each test case is described in a standard summary, which includes benchmark target solutions. A numerical code is considered as compliant with the aforementioned standard, providing the solutions for the test cases are within the tolerances for set physical point temperatures and total heat flow. Analyses were conducted using CalculiX suite, an open source code that can build, solve and post-process finite element (FE) models. All FE models were discretized with both first and second order elements and their results compliant with the reference solutions