Mechanical Engineering - Research Publications
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ItemSimulation of large-eddy-break-up device (LEBU) in a moderate Reynolds number turbulent boundary layer(Springer, 2016-08-11)A well-resolved large eddy simulation (LES) of a large-eddy break-up (LEBU) device in a spatially evolving turbulent boundary layer is performed with, Reynolds number, based on free-stream velocity and momentum-loss thickness, of R e θ ≈ 4300. The implementation of the LEBU is via an immersed boundary method. The LEBU is positioned at a wall-normal distance of 0.8 δ (δ denoting the local boundary layer thickness at the location of the LEBU) from the wall. The LEBU acts to delay the growth of the turbulent boundary layer and produces global skin friction reduction beyond 180δ downstream of the LEBU, with a peak local skin friction reduction of approximately 12 %. However, no net drag reduction is found when accounting for the device drag of the LEBU in accordance with the towing tank experiments by Sahlin et al. (Phys. Fluids 31, 2814, 1988). Further investigation is performed on the interactions of high and low momentum bulges with the LEBU and the corresponding output is analysed, showing a ‘break-up’ of these large momentum bulges downstream of the LEBU. In addition, results from the spanwise energy spectra show consistent reduction in energy at spanwise length scales for λ+z>1000 independent of streamwise and wall-normal location when compared to the corresponding turbulent boundary layer without LEBU.
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ItemNumerical and experimental investigations of the flow-pressure relation in multiple sequential stenoses coronary artery(SPRINGER, 2017-07)Virtual fractional flow reserve (vFFR) has been evaluated as an adjunct to invasive fractional flow reserve (FFR) in the light of its operational and economic benefits. The accuracy of vFFR and the complexity of hyperemic flow simulation are still not clearly understood. This study investigates the flow-pressure relation in an idealised multiple sequential stenoses coronary artery model via numerical and experimental approaches. Pressure drop is linearly correlated with flow rate irrespective of the number of stenosis. Computational fluid dynamics results are in good agreement with the experimental data, demonstrating reasonable accuracy of vFFR. It was also found that the difference between data obtained with steady and pulsatile flows is negligible, indicating the steady flow may be used instead of pulsatile flow conditions in vFFR computation. This study adds to the current understanding of vFFR and may improve its clinical applicability as an adjunct to invasively determined FFR.
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ItemCFD simulations of vertical surface piercing circular cylinders and comparison against experiments(Australian fluid mechanics society, 2018)When predicting the susceptibility of a submarine to above water detection, it is important to consider the impact of the wake generated by the periscope(s). Computational Fluid Dynamics (CFD) tools can be used to predict the physical size and shape of the wake, which can be combined with periscope models for input into detectability prediction models. For this application, it is important that CFD predictions of the wake are accurate not only in the mean calculations, but that the physical characteristics of the wake are captured at instantaneous snapshots in time. In a previous experimental study, Keough et al. [10] presented time resolved measurements of the wake from vertical surface piercing cylinders, utilising an automated method of extracting these measurements as a function of time from video recordings of the experiment. In the present work, CFD simulations have been performed to model this experimental data set. The open source CFD software Caelus was used, with the improved Defence Science and Technology Group version of vofSolver—the multiphase volume of fluid solver. A numerical wave gauge is implemented in order to measure the free surface elevation during the simulation and this data is compared to bow wave data obtained from animations of the CFD results, using the same automated visual tracking technique utilised for the experimental measurements. Analysis of these time-resolved measurements is performed, comparing transient statistics and spectral characteristics of the CFD predictions against the experimental data.
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ItemTime Resolved Measurements of Wake Characteristics from Vertical Surface-Piercing Circular Cylinders(Australasian Fluid Mechanics Society, 2016)
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ItemNo Preview AvailableNumerical investigation of the behaviour of wall shear stress in three-dimensional pulsatile stenotic flows(Australasian Fluid Mechanics Society (AFMS), 2014)