Two Point Space-Time Correlation of Density Fluctuations Measured in High Velocity Free Jets

Two-point space-time correlations of air density fluctuations in unheated, fully-expanded free jets at Mach numbers M(sub j) = 0.95, 1.4, and 1.8 were measured using a Rayleigh scattering based diagnostic technique. The molecular scattered light from two small probe volumes of 1.03 mm length was measured for a completely non-intrusive means of determining the turbulent density fluctuations. The time series of density fluctuations were analyzed to estimate the integral length scale L in a moving frame of reference and the convective Mach number M(sub c) at different narrow Strouhal frequency (St) bands. It was observed that M(sub c) and the normalized moving frame length scale L*St/D, where D is the jet diameter, increased with Strouhal frequency before leveling off at the highest resolved frequency. Significant differences were observed between data obtained from the lip shear layer and the centerline of the jet. The wave number frequency transform of the correlation data demonstrated progressive increase in the radiative part of turbulence fluctuations with increasing jet Mach number.

[1]  J. Wills,et al.  On convection velocities in turbulent shear flows , 1964, Journal of Fluid Mechanics.

[2]  J. Panda,et al.  Experimental investigation of density fluctuations in high-speed jets and correlation with generated noise , 2002, Journal of Fluid Mechanics.

[3]  Michael Fisher,et al.  Correlation measurements in a non-frozen pattern of turbulence , 1964, Journal of Fluid Mechanics.

[4]  J. Freund.  Noise sources in a low-Reynolds-number turbulent jet at Mach 0.9 , 2001, Journal of Fluid Mechanics.

[5]  James C Laurence,et al.  Intensity, Scale, and Spectra of Turbulence in Mixing Region of Free Subsonic Jet , 1956 .

[6]  Aerodynamic Characterisation of a Supersonic Jet using Two-point Laser Doppler Velocimetry , 2003 .

[7]  James R. DeBonis,et al.  Large-Eddy Simulation of a Turbulent Compressible Round Jet , 2002 .

[8]  Michael Fisher,et al.  The characteristics of the turbulence in the mixing region of a round jet , 1963, Journal of Fluid Mechanics.

[9]  D. G. Crighton,et al.  Basic principles of aerodynamic noise generation , 1975 .

[10]  K. A. Elam,et al.  Further Progress in Noise Source Identification in High Speed Jets via Causality Principle , 2003 .

[11]  J. Seiner,et al.  On the Two Components of Turbulent Mixing Noise from Supersonic Jets , 1996 .

[12]  William H. Press,et al.  Numerical Recipes: FORTRAN , 1988 .

[13]  M. Wernet,et al.  Measurements of the Aeroacoustic Sound Source in Hot Jets , 2004 .

[14]  Marcus Harper-Bourne,et al.  Jet Noise Turbulence Measurements , 2003 .

[15]  K. A. Elam,et al.  Time-Averaged Velocity, Temperature and Density Surveys of Supersonic Free Jets , 2004 .

[16]  Modelling Self and Shear Noise Mechanisms in Anisotropic Turbulence , 2003 .

[17]  C. Tam,et al.  Jet Mixing Noise from Fine-Scale Turbulence , 1998 .

[18]  Russell H. Thomas,et al.  Development of a Jet Noise Prediction Method for Installed Jet Configurations , 2003 .

[19]  A. Townsend.  The Structure of Turbulent Shear Flow , 1975 .

[20]  M. E. Goldstein,et al.  On identifying the true sources of aerodynamic sound , 2005, Journal of Fluid Mechanics.

[21]  Space–time correlation measurements of high-speed axisymmetric jets using optical deflectometry , 2005 .

[22]  A. Hussain,et al.  Structure of turbulent shear flows , 1987 .