Turbulent Radiation Statistics of Exhaust Plumes Exiting from a Subsonic Axisymmetric Nozzle

Improved understanding of radiation emissions from exhaust plumes are needed for safety applications. Relevant literature has focused on characterizing mean radiation properties of exhaust plumes. Turbulent radiation properties reported for flames have been used to provide insight into scalar distribution within the flows, improve understanding of turbulence radiation interactions, and estimate integral time and length scales. Motivated by this, radiation intensity measurements of subsonic exhaust plumes were acquired using a high-speed infrared camera (up to 11,300 Hz). The mean, root mean square, probability density function, auto and spatial correlation coefficients, integral time and length scales, and power spectral density functions of the measured radiation intensity are reported near the tip of the potential core and downstream. Axial and radial variation in radiation intensity fluctuations is similar to those reported for flames. Autocorrelation coefficients of the radiation intensity are approximated reasonably well by exponential curves. Integral time and length scales increase monotonically downstream of the core region and are consistent with Taylor's hypothesis. The break frequency and slope of the normalized power spectral density function are comparable to those reported for turbulent jet flames. These findings suggest that reacting flows can be used to predict trends in turbulent radiation properties of exhaust plumes.