Showing papers by "Roger E. A. Arndt published in 1979"
01 Jul 1979
TL;DR: In this paper, an experimental study of the narrowband spectra of radiated sound from subsonic jets is discussed, and it is found that the acoustic field is Reynolds-number-dependent below a Reynolds number of about 200,000.
Abstract: An experimental study of the narrowband spectra of radiated sound from subsonic jets is discussed. It is found that the acoustic field is Reynolds-number-dependent below a Reynolds number of about 200,000. This has important implications for the study of coherent structures as radiators of sound.
5 citations
TL;DR: In this paper, the authors studied the spectrum characteristics of the acoustic field generated by subsonic jets at low Reynolds numbers in terms of a dimensionless power spectral density and found that the variation of the sound magnitude of the spectrum is an increasing function of the Reynolds number.
Abstract: The narrowband spectral characteristics of the acoustic field generated by subsonic jets at low Reynolds numbers were studied in terms of a dimensionless power spectral density. It was found that the variation of the sound magnitude of the spectrum is an increasing function of the Reynolds number. The maximum level of the spectrum is not a linear function of the Reynolds number. The spectra are insensitive to Reynolds number above a critical value of about 100,000. Up to Reynolds number of this magnitude, the peak Strouhal frequency observed at 30 deg emission angle is identical with that at 90 deg for any exit Mach number. At higher Reynolds number the peak Strouhal number increases with increasing emission angle. The peak Strouhal number was found to be about 0.2, which is in agreement with previous findings that a few discrete modes at a Strouhal number of around 0.2 in low Reynolds number supersonic jets are powerful noise generators.
3 citations
TL;DR: In this article, the aerodynamic jet axis, defined as the locus of points in the flow at which the turbulence intensity is minimum, was determined and the deviations from the geometrical jet axis were on the order of 2-4% of the nozzle diameter.
Abstract: Turbulence intensity measurements were made in three different-size jets at various Mach numbers and the aerodynamic jet axis, defined as the locus of points in the flow at which the turbulence intensity is minimum, was determined. The deviations from the geometrical jet axis were on the order of 2-4% of the nozzle diameter, and the pure jet axis had the form of a helical wave. A similar asymmetry in the radiated noise was also noted. The measured circumferential distribution of rms fluctuating velocity signals confirmed the asymmetry of even a circular jet.