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An empirical model for transition to turbulence in oscillatory flows in straight tubes is proposed. The model, fashioned after a correlation for transition of a boundary layer on a flat plate, yields the laminar flow momentum thickness Reynolds number that must be met before transition to turbulence will occur. The transition point is located by comparing this to the actual momentum thickness Reynolds number. Since in one-dimensional computation, as is typically employed in engine simulation codes, the momentum thickness Reynolds number cannot be computed, a scheme is proposed for estimating it in terms of the position within the cycle, the maximum value of the diameter Reynolds number within the cycle, Remax, and the dimensionless frequency, Valensi number, Va. Another parameter required in the calculation of the point of transition is the turbulence intensity value within the core flow and external to the boundary layer.

Oscillating fluid flow (zero mean) with heat transfer, between two parallel plates with a sudden change in cross section, was examined computationally. The flow was assumed to be laminar and incompressible with inflow velocity uniform over the channel cross section but varying sinusoidally with time. Over 30 different cases were examined; these cases cover wide ranges of Remax (187.5 to 30 000), Va (1 to 350), expansion ratio (1:2, 1:4, 1:8, and 1:12) and Ar (0.68 to 4). Three different geometric cases were considered (asymmetric expansion/contraction, symmetric expansion/contraction, and symmetric blunt body). The heat transfer cases were based on constant wall temperature at higher (heating) or lower (cooling) value than the inflow fluid temperature. As a result of the oscillating flow, the fluid undergoes sudden expansion in one-half of the cycle and sudden contraction in the other half.

With consideration of the importance (for oil passing and blow-by) of the issue of three-dimensional deformation of piston rings in a cylinder due to either installation stress, or operational gas, friction, and thermal loads the subject of piston ring distortions still generates continuing interest. The current paper demonstrates application of a mathematical model developed in the former works of the authors for analysis of the distortions of arbitrary cross-section rings loaded by tangential force. Applications of the model to the several typical cross-sections are given for illustration. The work is a necessary step for the development of a comprehensive three-dimensional theory of piston ring installation and operational distortions.

The objective of this paper is to present the results of an investigation of elastic distortions of split piston rings that are used in lubricated and non-lubricated air brake compressors. Concepts of advanced stress analysis and Finite Element Analysis (FEA) have been employed in this study. The analysis of elastic distortions (twist) of piston rings due to the installation stresses has been quite poorly documented in the technical literature. As a result, unjustifiable engineering assumptions are some time made which result in misleading design solutions. This paper demonstrates analytically and with the support of FEA the mechanical/geometrical parameters of a split ring which affect the twist of the ring during the installation in the cylinder bore, and the calculated magnitude of this twist along the ring circumference.