Influence of Turbulent Fluctuations on the Radiation Intensity Emitted from Exhaust Plumes

Measured and computed mean and fluctuating radiation intensities are reported for a subsonic exhaust plume and used to characterize the influence of turbulent fluctuations on mean radiation properties. Narrowband radiation intensity measurements were acquired using an infrared camera fitted with a narrowband filter (4.34 +/- 0.1 mu m). Unsteady three-dimensional calculations were used to estimate both time-dependent and mean temperature and partial pressure values of the exhaust species in the flow. From these scalar values the mean and root mean square of the radiation intensity were calculated using a narrowband radiation model. Axial distributions of the calculated intensities based on the time-dependent quantities show trends similar to those measured, but consistently overpredict the intensity by 40%. Intensity distributions based on mean scalars were in better quantitative agreement, but decay more rapidly downstream than experimental data. Turbulent fluctuations have little effect on the mean radiation intensity near the nozzle exit, but they become increasingly more important downstream in the flow. The influence of turbulent fluctuations on mean intensity values increases with radial distance from the centerline. This trend correlates to increases in normalized fluctuations in the temperature and radiation intensity.