Turbulent swirling flow in short cylindrical chambers

The effects of aspect ratio (L/D) on the rate of decay of swirl in a cylindrical chamber were experimentally studied using the Laser-Doppler-Anemometry technique. Preliminary measurements revealed that water should be used as working fluid; the results pertaining to air were inferred from Reynolds number similarity. The steady-state measurements revealed that a solid body type of rotation can be generated by a disc whose surface has been uniformly roughened. The effect of aspect ratio on the rate of decay of such flow field was studied in three chambers with aspect ratios in the range of interest to engine combustion. Experimental results showed a faster decay rate in the shorter chamber (i.e. smaller aspect ratio). This was attributed to the stronger swirl driven secondary flow pattern in the shorter chamber. A mathematical model describing axi-symmetric, decaying, turbulent swirling flow inside a short cylindrical chamber was also developed. The model was numerically solved, using the control-volume analysis, to provide insight on swirl decay in engines. The model validation was based on experimental observations. Turbulence parameters were represented by a two-equation turbulence model, modified for streamline curvature effects. The ad-hoc curvature modification of the standard k-e model proposed by Launder et al. and the mixing energy model developed by Saffman-Wilcox-Traci (SWT) were used to account for curvature effects. The analysis of steady flow between two long concentric cylinders, established the superiority of the latter over the former method. The SWT model was also successfully used in reproducing previously published experimental results, pertaining to decaying swirling flow field (mean velocity and turbulence intensity) in a short cylinder. The calculated turbulence intensity profile revealed that swirl promotes anisotropic turbulence. The validated numerical model was used to predict the effect of aspect ratio on the rate of decay of the flow field observed by the experimental measurements in the present study. The overall prediction of decay rate was successful, leading to the conclusion that Wilcox and Chambers model can be used in predicting the behaviour of two-dimensional transient turbulent swirling flows.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat