A Discussion of the Effects of Sound on Jets and Flueric Devices

In designing fluid amplifiers it is important to know the conditions that affect a jet. These conditions generally fall into two general categories, signal and environment. Jet sensitivity to sound encompasses both categories; it therefore becomes important to understand the jet-sound relationship. This knowledge is useful in designing fluidic devices sensitive to sound signals or relatively insensitive to a noise environment. Laboratory experiments were performed which show that the spread of a bounded, two-dimensional jet increases when exposed to a sound field. From experiments conducted on smoke jets, it was concluded that for a given sound frequency the increase of the jet spread is dependent on the sound amplitude; moreover, the sound-sensitive jet has a frequency response bandwidth that contains a maximum, and both maximum and response band shift toward higher frequencies with increasing nozzle exit velocities. As the degree of turbulence of a jet increases, larger amplitude sound signals are needed to affect the jet. Using the Reynolds number as an indicator of jet turbulence and knowledge of the relationship of sound frequency to jet Reynolds number, one can then predict the sound or noise frequency that will disturb a jet in a flueric device.