Static Characteristics of Shrouded Acoustically Controlled Turbulence Amplifiers

Abstract

The static characteristics of shrouded, acoustically controlled turbulence amplifiers are investigated. The main variables are control sound pressure level and frequency, shroud diameter, gap length and supply flow conditions. Existing analytical and empirical relationships are evaluated. It is found that Bell’s analytical procedure [1] for unshrouded, flow controlled turbulence amplifiers reasonably describes the laminar jet pressure recovery of the amplifiers used in this investigation. The turbulent recovery pressure given by Bell’s procedure is not in agreement with the experimental results of this investigation. A “jump” in the characteristic frequency (defined as the control sound frequency to which the device is most sensitive) occurs as the Reynolds number of the emitter tube is increased. The lower characteristic frequency can be predicted by an advanced Helmholtz resonator theory. Further, the acoustically controlled, unlike the flow controlled, turbulence amplifier can be operated in the proportional mode over a limited range of experimental variables.