Subharmonic nonlinear acoustic resonances in open tubes. Part II: Experimental investigation of the open-end boundary condition

Abstract

Nonlinear oscillations driven by a piston which oscillates near one-half of the fundamental frequency of an open tube are studied. A simple model for the boundary condition at the open end of the tube, which allows for arbitrary losses during inflow and outflow, is investigated. Experimental results are presented which lead to the determination of the relationship between departures from Bernoulli flow during inflow and outflow. It is shown that rounded mouth pieces show very small losses, presumably due to nonsteadyflow effects. Sharp mouth pieces exhibit extremely large losses, much larger than in steady-flow jets. The sources of the large variation of end losses with relatively small changes of mouth geometry and of large frequency dependence exhibited by the end losses in sharp-lipped mouths are not understood.