Schulich School of Engineering
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With an annual average of 25 internationally recognized research chairs, more than 160 faculty members and 1,200 graduate students, the Schulich School of Engineering at the University of Calgary is a powerhouse of research and innovation.
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Browsing Schulich School of Engineering by Department "Mechanical and Materials Engineering"
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Item Open Access Flame acceleration enhancement by distributed ignition points(Journal of Propulsion and Power, 2005) Ciccarelli, Gaby; Johansen, Craig; Hickey, MarkThis paper reports on the investigation of a novel method for promoting flame acceleration leading to detonation initiation in a tube. A common method used to initiate a detonation wave is via flame acceleration in an obstacle laden tube. Previous studies with fuel-air mixtures have shown that the measured detonation run-up distance, and corresponding run-up time, is too long for a PDE application. The objective of the present investigation is to enhance the flame acceleration process that leads to DDT by using multi-point ignition. Experiments were performed in a 3.05 m long, 14 cm inner-diameter tube equipped with a primary igniter mounted centrally on the tube endplate. Equally spaced orifice plates were placed in the first 2 m of the tube. A bank of four circumferentially equally spaced automotive spark plugs are located after each of the first three orifice plates. The firing time of each igniter bank is variable. The results indicate that flame acceleration is augmented early in the tube and maintained to the end. The reduction in the distance required for the flame to accelerate to a velocity on the order of the speed of sound in the combustion products is modest, on the order of 10%. However, the reduction in the time required to reach this velocity is much more pronounced which has an impact on the PDE cycle frequency. Flame acceleration was further enhanced by replacing the first few orifice plates with perforated plates with the same total flow area, e.g., the flame run-up distance was shortened by 30%. However, detonation initiation was not observed over the 3 m length of the tube in stoichiometric propane-air mixtures.Item Open Access Numerical simulations of the flow field ahead of an accelerating flame in an obstructed channel(2010) Johansen, Craig; Ciccarelli, GabyThe development of the unburned gas flow field ahead of a flame front in an obstructed channel was investigated using large eddy simulation (LES). The standard Smagorinsky–Lilly and dynamic Smagorinsky–Lilly subgrid models were used in these simulations. The geometry is essentially two-dimensional. The fence-type obstacles were placed on the top and bottom surfaces of a square cross-section channel, equally spaced along the channel length at the channel height. The laminar rollup of a vortex downstream of each obstacle, transition to turbulence, and growth of a recirculation zone between consecutive obstacles were observed in the simulations. By restricting the simulations to the early stages of the flame acceleration and by varying the domain width and domain length, the three-dimensionality of the vortex rollup process was investigated. It was found that initially the rollup process was two-dimensional and unaffected by the domain length and width. As the recirculation zone grew to fill the streamwise gap between obstacles, the length and width of the computational domain started to affect the simulation results. Three-dimensional flow structures formed within the shear layer, which was generated near the obstacle tips, and the core flow was affected by large-scale turbulence. The simulation predictions were compared to experimental schlieren images of the convection of helium tracer. The development of recirculation zones resulted in the formation of contraction and expansion regions near the obstacles, which significantly affected the centerline gas velocity. Oscillations in the centerline unburned gas velocity were found to be the dominate cause for the experimentally observed early flame-tip velocity oscillations. At later simulation times, regular oscillations in the unburned streamwise gas velocity were not observed, which is contrary to the experimental evidence. This suggests that fluctuations in the burning rate might be the source of the late flame-tip velocity oscillations. The effect of the obstacle blockage ratio (BR) on the development of the unburned gas flow field was also investigated by varying the obstacle height. Simulation predictions show favorable agreement with the experimental results and indicate that turbulence production increases with increasing obstacle BR.