Vibration Isolation of Pressure Transducers for Determination of Acoustic Environment

Abstract

Measurement of pressure fluctuations due to acoustic environment is important in the investigation of turbulent flow phenomena associated with several classes of aerospace problems. These measurements, utilizing piezoelectric transducers, are accompanied by noise from vibrations of the structure on which the transducers are mounted. Two schemes for the vibration isolation of the transducers are experimentally investigated. These are: individual isolation of transducers, and isolation of an insert on which the transducers are mounted. Experiments were conducted in a 14 in.×14-in. supersonic wind tunnel at a nominal Much number of 1.96 and stagnation pressures of 30 and 45 psia. Comparison of the spectra of the pressure fluctuations measured by transducers mounted on a flat wall of the tunnel shows that structural noise above 3 kc/sec may be eliminated by any one of the two schemes, and that below 3 kc/sec may be eliminated by any one of the two schemes, and that below 3 kc/sec the structural noise is considerably reduced by these isolation techniques. In order to attain further insight into the manner in which a pressure transducer is affected by structural vibrations, coherence functions have been calculated for structural noise and observed pressure fluctuations.