http://hdl.handle.net/10204/907 Sat, 25 May 2013 02:19:15 GMT 2013-05-25T02:19:15Z http://hdl.handle.net/10204/6636 Title: Development of a compressive surface capturing formulation for modelling free-surface flow by using the volume-of-fluid approach Authors: Heyns, JA; Malan, AG; Harms, TM; Oxtoby, OF Abstract: With the aim of accurately modelling free-surface flow of two immiscible fluids, this study presents the development of a new volume-of-fluid free-surface capturing formulation. By building on existing volume-of-fluid approaches, the new formulation combines a blended higher resolution scheme with the addition of an artificial compressive term to the volume-of-fluid equation. This reduces the numerical smearing of the interface associated with explicit higher resolution schemes while limiting the contribution of the artificial compressive term to ensure the integrity of the interface shape is maintained. Furthermore, the computational efficiency of the the higher resolution scheme is improved through the reformulation of the normalised variable approach and the implementation of a new higher resolution blending function. The volume-of-fluid equation is discretised via an unstructured vertex-centred finite volume method and solved via a Jacobian-type dual time-stepping approach. Description: Copyright: 2012 Wiley-Blackwell. This is the pre/post print version of the work. The definitive version is published in International Journal for Numerical Methods in Fluids, vol. 71(6), pp 788-804 Fri, 01 Jun 2012 00:00:00 GMT http://hdl.handle.net/10204/6636 2012-06-01T00:00:00Z http://hdl.handle.net/10204/6617 Title: A weakly compressible free-surface flow solver for liquid–gas systems using the volume-of-fluid approach Authors: Heyns, JA; Malan, AG; Harms, TM; Oxtoby, OF Abstract: This paper presents a weakly compressible volume-of-fluid formulation for modelling immiscible high density ratio two-fluid flow under low Mach number conditions. This follows findings of experimental analyses that concluded the compressibility of the gas has a noteworthy effect on predicted pressure loads in liquid–gas flow in certain instances. With the aim of providing a more accurate numerical representation of dynamic two-fluid flow, the solver is subsequently extended to account for variations in gas densities. A set of governing equations is proposed, which accounts for the compressible properties of the gas phase in a manner which allows for a computationally efficient numerical simulation. Furthermore, the governing equations are numerically expressed so that they allow for large variations in the material properties, without introducing notable non-physical oscillations over the interface. For the discretisation of the governing equations an edge-based vertex-centred finite volume approach is followed. The developed solver is applied to various test cases and demonstrated to be efficient and accurate. Description: Copyright: 2012 Elsevier. This is the post print version of the work. The definitive version is published in Journal of Computational Physics, vol. 240, pp 145-157 Wed, 01 May 2013 00:00:00 GMT http://hdl.handle.net/10204/6617 2013-05-01T00:00:00Z http://hdl.handle.net/10204/6545 Title: Microstructure characterization of laser-deposited titanium carbide and zirconium-based titanium metal matrix composites Authors: Ochonogor, OF; Meacock, C; Pityana, SL; Popoola, PAI; Dutta Majumder, J Abstract: Laser metal deposition (LMD) is an additive manufacturing technique whereby a stream of metal powder is consolidated by a focused laser beam on the surface of a substrate or engineering component. The interaction zone between the laser beam and powder particles is scanned superficially, generating tracks of deposited material. The tracks are overlapped in a deposition strategy in accordance with slices of a CAD model. Successive layers of material are built up to fabricate a near net shape part. In this work, the technique is used to fabricate metal matrix composites (MMCs) by using an elementally blended feedstock combining metal and ceramic powders in the melt pool, which melt and solidify to create the required morphology. Ti6Al4V + TiC MMCs were produced with 10, 20, and 30 vol.% reinforcing ceramic, and Zr + TiC MMCs were fabricated with 10, 20, and 30 vol.% TiC. The deposited thin walls were analysed using optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and indentation testing. In both systems, the analysis revealed the presence of partially melted TiC particles embedded in the metal matrix along with fine dendrites of re-solidified ceramic. The dendritic structures in the Ti-based composites were confirmed as TiC, whereas in the Zr-based composite the Zr metal reacts with the TiC to form ZrC, leaving Ti in solid solution. Both the MMCs show an increase in microhardness with increasing ceramic (carbide) content, reaching a peak HV0.1 value of 500 in the Zr- based MMC and HV0.1 of 550 in the Ti based MMC. Description: Copyright: 2012 Southern African Institute of Mining and Metallurgy. Sat, 01 Sep 2012 00:00:00 GMT http://hdl.handle.net/10204/6545 2012-09-01T00:00:00Z http://hdl.handle.net/10204/6504 Title: Three-component particle image velocimetry in a generic can-type gas turbine combustor Authors: Meyers, BC; Snedden, GC; Meyer, JP; Roos, TH; Mahmood, GI Abstract: A stereoscopic particle image velocimetry (PIV) system was used to obtain the velocity field of a can-type combustor in the non-reacting condition. In order for these measurements to be taken, an optically accessible can-type forward flow combustor was manufactured. The combustor has a 10-vane swirler in the dome as well as a primary zone with six 9.5 mm holes, a secondary zone with eight 5 mm holes and a dilution zone with ten 11.8 mm holes. The two cooling rings have 30 and 50 x 1.2 mm holes and are placed between the three zones. The main flow features were captured such as the recirculation zones and jets. The more subtle features such as flow entering the swirler, entering the dilution holes from the annulus, and converging into smaller annuli around the secondary and dilution zones were also evident in some sections of the data. An unexpected flow recirculation was observed in the dilution zone. The departure of the flow from the recirculation regions to join the bulk flow in the dilution zone was also shown. Description: Copyright: 2012 SAGE Publications. This is an ABSTRACT ONLY. The definitive version is published in Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, Vol. 226(7), pp 892-906. Thu, 01 Nov 2012 00:00:00 GMT http://hdl.handle.net/10204/6504 2012-11-01T00:00:00Z