Research on Wave Phenomena in Hydraulic Lines : 10th Report, Experimental Discussion on Unsteady Nonlinearity of Orifice Flows

Abstract

This report intends to experimentally reveal the fundamental differences between the steady and unsteady nonlinearities of orifice flows. The same measurements as in the foregoing paper are conducted in pulsating oil flows through orifices. Separating nonlinear components from total pressure drops and plotting them versus flow rates yields another hysteresis curve which represents the unsteady nonlinearity alone. It turns out that this curve invariably takes on similar inflection and counterclockwise hysteresis, and on the average lies below the steady-state loss. These findings lead to a hypothesis that eddies which bring about nonlinear energy dissipation in orifice flows tend to resist the change of magnitude, which is here called 'eddy inertia'. An idea of time lag inherent in the nonlinear loss helps embody this hypothesis as an empiric formula. This formula successfully explains the peculiar behaviors of hysteresis curves and Bolt's observation that the nonlinearity reduces the orifice reactances.