Experimental Validation of a Time Domain Cavitation Model for Switched Inertance Circuits

Switched inertance hydraulic systems are switch mode fluid power circuit topologies that allow the load pressure to be modulated in an efficient manner. A unique feature of these circuits is a long, small diameter, inertance tube, which stores energy in the fluid kinetic domain during a switching cycle. A barrier to application of these circuits is that current models require an elevated reservoir pressure, which is difficult to implement in practice. Research has focused on analyzing inertance tube wave delay effects in the frequency domain, which necessarily excludes non-linear physical phenomena such as cavitation and pressure dependent wave speed. A circuit with an ambient reservoir pressure exposes the fluid in the inertance tube to local pressure conditions where these non-ideal behaviors may have a strong effect on system dynamics. In this paper, a method of characteristics cavitation model with unsteady friction is presented that accurately captures the incidence and severity of cavitation in a long pipeline undergoing cyclic high and low pressure boundary conditions. This model is validated experimentally by examining the pressure response in a 3.95m steel pipeline with an upstream switching valve capable of 0.5ms transition at 120Hz. Experiments are conducted over a range of switching frequencies at 60% duty. The proposed pipeline model can be used to predict conditions leading to cavitation as well as help develop cavitation avoidance strategies, such as soft switching and utilization of line resonance.