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Browsing Faculty of Computing, Engineering and Media by Author "Abdalla, I. E."
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Item Metadata only Coherent structures and flow topology of transitional separated-reattached flow over two and three dimensional geometrical shapes(American Institute of Physics, 2017) Diabil, H. A.; Abdalla, I. E.; Li, X. K.Large-scale organized motions (commonly referred to coherent structures) and flow topology of a transitional separated-reattached flow have been visualised and investigated using flow visualisation techniques. Two geometrical shapes including two-dimensional flat plate with rectangular leading edge and three-dimensional square cylinder are chosen to shed a light on the flow topology and present coherent structures of the flow over these shapes. For both geometries and in the early stage of the transition, two-dimensional Kelvin-Helmholtz rolls are formed downstream of the leading edge. They are observed to be twisting around the square cylinder while they stay flat in the case of the two-dimensional flat plate. For both geometrical shapes, the two-dimensional Kelvin-Helmholtz rolls move downstream of the leading edge and they are subjected to distortion to form three-dimensional hairpin structures. The flow topology in the flat plate is different from that in the square cylinder. For the flat plate, there is a merging process by a pairing of the Kelvin-Helmholtz rolls to form a large structure that breaks down directly into many hairpin structures. For the squire cylinder case, the Kelvin-Helmholtz roll evolves topologically to form a hairpin structure. In the squire cylinder case, the reattachment length is much shorter and a forming of the three-dimensional structures is closer to the leading edge than that in the flat plate case.Item Metadata only Computational analysis and flow structure of a transitional separated-reattached flow over a surface mounted obstacle and a forward-facing step.(Taylor and Francis, 2009) Yang, Z.; Cook, M. J.; Abdalla, I. E.Item Metadata only Computational visualisation of separated-reattached transitional flow on a blunt plate.(Begell House, 2004) Abdalla, I. E.; Yang, Z.Item Metadata only Effects of free-stream turbulence on a transitional separated-reattached flow over a flat plate with a sharp leading edge.(Elsevier Science, 2009) Yang, Z.; Abdalla, I. E.Item Metadata only Effects of free-stream turbulence on large-scale coherent structures of separated boundary layer transition.(John Wiley, 2005-06-01) Abdalla, I. E.; Yang, Z.Item Metadata only Large-eddy simulation of buoyancy-driven natural ventilation in an enclosure with a point heat source.(2007-06-01) Cook, M. J.; Abdalla, I. E.; Rees, S. J.; Yang, Z.Item Metadata only Numerical study of a separated - reattached flow on a blunt plate(American Institute of Aeronautics and Astronautics Journal, 2005-12-01) Abdalla, I. E.; Yang, Z.Item Metadata only Numerical study of the instability mechanism in transitional separating-reattaching flow(Elsevier, 2004-12-01) Abdalla, I. E.; Yang, Z.Item Metadata only Numerical study of thermal plume characteristics and entrainment in an enclosure with a point heat source.(Hong Kong Poly University, 2009) Abdalla, I. E.; Cook, M. J.; Hunt, G. R.Item Metadata only Numerical study of transitional separated-reattached flow over surface-mounted obstacles using large-eddy simulation(John Wiley, 2006-11-01) Abdalla, I. E.; Cook, M. J.; Yang, Z.Item Metadata only On coherent structures in a separated/reattached flow(2008-04) Yang, Z.; Abdalla, I. E.It is well known that large-scale organised motions, usually called coherent structures, exist in many transitional and turbulent flows. The topology and range of scales of coherent structures change widely in different flows. However, it is not well established what kind of large-scale coherent structures exists in separated/reattached transitional flows. Large Eddy Simulation (LES) with a dynamic subgrid-scale model is employed to investigate a separated boundary layer transition under 2% free stream turbulence level and without free stream turbulence on a flat plate with a blunt leading edge. Flow visualization is employed to show the entire transition process leading to breakdown to turbulence and large-scale coherent structures have been identified at various stages of the transition process. However, there are some noticeable difference between the flow case with and without free stream turbulence. The Kelvin-Helmholtz rolls, which are clearly visible under no free stream turbulence (NFST), are not so clearly visible under 2% free steam turbulence (FST) case. The Lambda-shaped vortical structures which can be clearly seen in the NFST case can hardly be identified in the FST case. Generally speaking, the effects of free-stream turbulence have led to an early breakdown of the separated boundary layer and hence increased the randomisation in the vortical structures, degraded the spanwise coherence of those large-scale structures.Item Metadata only Theoretical and experimental analysis of ultrasonic cross correlation flow measurement technology.(Curran Associates, 2010) Gurevich, A.; Selvaratnarajah, S.; Abdalla, I. E.