Axial transition of oscillatory oil flow in front of reciprocating piston (Numerical calculation and LDV measurement)

In front of a reciprocating piston in a pipe containing fluid, the velocity profile is assumed to vary continuously in the axial direction from a uniform one to that of an ordinary oscillatory viscous pipe flow. The present paper deals with theoretical and experimental discussions of this subject. Numerical calculations have indicated that the transition of velocity profiles is completed within a pipe radius away from the piston. In order to experimentally verify this finding, an LDV with a counter-type signal processor is used to measure velocities in oscillatory oil flows close to a reciprocating piston. Although a counter is usually not used for measuring unsteady flows, it has proved applicable to periodic flows when the data within the same range of phase angle are separately collected and stochastically processed in the same way as in an ordinary steady measurement. The measurements thus carried out have given satisfactory results which agree with the theoretical predictions.