Excitation Of Displacer Motion In A Fluidyne: Analysis And Experiment

In the most common design of liquid piston Stirling engines, an oscillating water column in a U-tube serves as the displacer. The motion of the water is maintained despite viscous and other flow losses by means of a second water column (usually referred to as the tuning line) that is connected to the displacer U-tube near to the expansion space. This second column, driven by the gas pressure changes in the working gas space, feeds energy into the oscillating displacer column by adding water to it when the water level, and therefore the potential energy, is high, and removing water when the level is lower. Several authors have published theoretical papers describing this process; most of the theories are mathematically equivalent. This paper describes some actual experimental results obtained with a large water-filled U-tube (representing a fluidyne displacer) excited by a second, piston-driven water column. The results are in good agreement with the predictions of a simple theory whose equations are illustrated by the vector, or phasor, method of representing the motions of coupled systems.