Measurements of the unsteady mass flux deficit of a turbulent spot: implications for boundary layer transition noise

Michael H. Krane, Wayne R. Pauley

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Unsteady velocity field measurements of an isolated, artificially generated turbulent spot were made in a zero-pressure gradient laminar boundary layer in a water channel facility. These measurements were used to provide quantitative information concerning the local large-scale boundary layer displacement thickness fluctuations due to the passage of a turbulent spot, which are believed to be an important sound source mechanism in boundary layer transition. Ensemble averaging of the velocity data was triggered on the spot generation. The unsteady mass flux deficit (MFD) was calculated from the ensemble-averaged velocity data taken at five streamwise (x) locations. At each location the amplitudes of the peaks in both the unsteady MFD and the unsteady velocity normal to the plate (vn), as well as the characteristic MFD rise times, ti, were deduced from the MFD time series. Comparing the results at different stations shows that ti and the peak MFD amplitude increases with x, while the peak amplitude of Vn increases early in the spot development, but reaches a maximum. For all these parameters, the rate of spatial growth is greatest in the most upstream portions of the boundary layer. The normalized rise time, UctiΔX, introduced by Lauchle (1981), was found to span a range of values 0.06 < UctiΔx < 0.74 over the locations we measured, with the lowest values again in the upstream end of the transition zone. Scaling analysis using these experimental results shows that the sound radiated by the large-scale motion due to an isolated turbulent spot increases as the spot grows and has a dipole character. Extrapolation to a natural transition zone indicates that sound radiation from the large-scale intermittent motion is highest in the middle part of the transition zone because the spot density is highest there.

Original languageEnglish (US)
Title of host publicationFlow-Structure and Flow-Sound Interactions
PublisherPubl by ASME
Pages133-145
Number of pages13
ISBN (Print)0791810801
StatePublished - Dec 1 1992
EventWinter Annual Meeting of the American Society of Mechanical Engineers - Anaheim, CA, USA
Duration: Nov 8 1992Nov 13 1992

Publication series

NameAmerican Society of Mechanical Engineers, Noise Control and Acoustics Division (Publication) NCA
Volume13

Other

OtherWinter Annual Meeting of the American Society of Mechanical Engineers
CityAnaheim, CA, USA
Period11/8/9211/13/92

All Science Journal Classification (ASJC) codes

  • Mechanical Engineering
  • Acoustics and Ultrasonics

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  • Cite this

    Krane, M. H., & Pauley, W. R. (1992). Measurements of the unsteady mass flux deficit of a turbulent spot: implications for boundary layer transition noise. In Flow-Structure and Flow-Sound Interactions (pp. 133-145). (American Society of Mechanical Engineers, Noise Control and Acoustics Division (Publication) NCA; Vol. 13). Publ by ASME.