Experimental studies of the noise produced in a supersonic nozzle by upstream acoustic and thermal disturbances

Citation

Auerbach, Jerome M. (1975) Experimental studies of the noise produced in a supersonic nozzle by upstream acoustic and thermal disturbances. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/z2x3-g471. https://resolver.caltech.edu/CaltechTHESIS:10172012-081901085

Abstract

A novel noise source mechanism whereby sound is produced by time-dependent temperature nonuniformities in a flow with a mean velocity gradient is investigated experimentally. The research is part of a theoretical and experimental study of this noise source initiated by Professor F. E. Marble.

A steady accelerating flow was produced in a rectangular supersonic nozzle with an entrance Mach number of 0.2, an exit Mach number of 1.38, and a throat area of 1 in.^2. A rotary valve bleed flow system and an electrical wire resistance heater upstream of the nozzle introduced mass flow and temperature fluctuations into the nozzle flow at frequencies up to 500Hz. Sound measurements were made at six positions along the nozzle and outside the nozzle assembly, which was enclosed in an anechoic chamber 10 ft. on a side.

All data acquisition and processing was done with a computer-controlled data acquisition system, making the experiment essentially "computerized.” By interfacing the control circuitry of the bleed flow and heater systems to the data acquisition system) a digital signal-averaging technique was developed which enabled the sound produced by the bleed flow and temperature fluctuations to be detected and accurately measured in high-level backgrounds of turbulent flow noise.

By synchronization of the bleed flow and heater, a pure temperature disturbance without an associated pressure disturbance caused by heating was produced. This pure temperature disturbance was found to produce sound upon being convected through the nozzle. The novel noise source mechanism was thus verified.

Excellent agreement was found between the nozzle sound measurements and one-dimensional small disturbance theory applied to the flow occurring in the nozzle.

External field measurements yielded jet noise levels and spectra agreeing with other reported studies, spatial variation of the sound field due to a pure pressure fluctuation at the nozzle exit, and cross correlation data between the external sound field and the pressure fluctuations at the nozzle exit.

Thesis Files