It is shown that the pressure signal measured at the outer edge of a jet mixing layer is entirely hydrodynamic in nature and provides a good measure of the large-scale structure of the turbulent ﬂow. Measurement of the pressure signal provides a unique opportunity to utilize proper orthogonal decomposition (POD) to deduce the streamwise structure. Since pressure is a scalar, a signiﬁcant reduction in the numerical and experimental complexity inherent in the analysis of velocity vector ﬁelds results.
The POD streamwise eigenfunctions show that the structure associated with any frequency–azimuthal mode number combination displays the general characteristics of ampliﬁcation–saturation–decay of an instability wave, all within about three wavelengths. High-frequency components saturate early in x and low-frequency components saturate further downstream, indicative of the inhomogeneous character of the ﬂow in the streamwise direction. Application of the POD technique allows the phase velocity to be determined taking into account the inhomogeneity of the ﬂow in the streamwise direction. The phase velocity of each instability wave (POD eigenvector) is constant and equal to 0.58Uj , indicating that the jet structure is non-dispersive. Using the shot-noise decomposition, a characteristic event is constructed. This event is found to contain evidence of both pairings and triplings of vortex structures. The tripling results in a rapid increase in the ﬁrst asymmetric (m = 1) component. On average, pairing occurs once every four Uj/D while tripling occurs once every 13Uj/D.
Arndt, R. E. A., Long, D. F., & Glauser, M. N. (1997). The proper orthogonal decomposition of pressure fluctuations surrounding a turbulent jet. Journal of Fluid Mechanics, 340, 1-33.
Copyright Cambridge University Press. Published article may be found at http://journals.cambridge.org/action/displayAbstract?aid=13425.
Air Force Office of Scientific Research, Office of Naval Research
Arndt, Roger E.A.; Long, D.F.; Glauser, M.N.
The proper orthogonal decomposition of pressure fluctuations surrounding a turbulent jet.
Cambridge University Press.
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