Theoretical and experimental investigations of transient flow in oil-hydraulic small-diameter pipe system

Abstract

This paper investigates unsteady flow phenomena in a new oil-hydraulic small-diameter pipeline apparatus at the Wrocław University of Science and Technology, Poland. The steel pipe section lengths can be either 2 or 7 m, and the internal pipe diameter 4 mm (micro-hydraulic system). Transient event was triggered by a rapid closure of a downstream end bi-directional poppet valve. Pressures and velocities were investigated at the pipe end points. The main objective was to investigate effects of valve action on pressure magnitudes and timing in a number of transient laminar flow situations. In the method of characteristics numerical simulations a quasi-steady and a novel computationally effective Urbanowicz’s convolution-based unsteady friction models were used, as well as a quadratic bi-directional poppet valve function boundary condition. Comparisons between measured and calculated results clearly show that the valve closure path and the unsteady friction control the effects of unsteadiness on attenuation, shape and timing of pressure pulses in a small-diameter pipeline system; however, the unsteady friction is less important for the cases characterized by a relatively large fluid hammer number.