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Title: A computational study of gas leak jets relevant to offshore structures.
Author: Simpson, Benjamin Alec Field.
ISNI:       0000 0001 3412 5790
Awarding Body: University of Herfordshire
Current Institution: University of Hertfordshire
Date of Award: 1998
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In the present research three dimensional, incompressible turbulent jet flows from sharp edged rectangular orifices were numerically simulated. Preliminary studies employing the standard k-E turbulence model stressed the sensitivity of the flow to the specification of turbulence quantities at the inlet. The definition of correct turbulence quantities at the inflow of large eddy simulations was also shown to be crucial for realistic simulations. Consequently, a novel computationally inexpensive boundary condition, that provided turbulence data with known energy, was developed and programmed into a commercial finite element code. The large eddy simulations provided instantaneous data that demonstrated the emergence of complex flow patterns within a short axial distance. The upstream geometry from the jet exit was not included in the present simulations. Therefore, the swirling motion and vortical structures observed could not be related to the different rates of contraction upstream of the discharge plane. In addition, saddle-backed profiles were observed in the long axis of the jet stream. The saddlebacked profiles were formed by a combination of the secondary motions and curvature of the streamlines due to the entrained fluid entering normally to the main jet stream. Turbulence quantities were quantified from the large eddy simulations and showed similar trends to the verifying experimental data. The round jet assumption used in the past to study gas leakage from pipework was found to be invalid in the near field. The simulations clearly illustrate differences between the flow field, the turbulence field, and the coherent structures of a rectangular jet and a round jet. Regions of high and low mixing between the escaping flammable gas and the surrounding air were identified in the large eddy simulations. Furthermore, the coherent structures in the shear layers that resulted in a flapping motion in the lateral direction of the jet, were recognised as important entrainment mechanisms. Numerical techniques have been developed that can be used to investigate gas leakage in detail. The time dependent numerical data provides valuable insight into the mixing mechanisms of the local gas/air mixture thus aiding the safer design of offshore structures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Fluid mechanics