A similarity study on the infrared radiation of solid rocket plume in different reduced-scale sizes

The similarity of the plume radiation of solid rocket engines in different reduced-scale sizes is important for studying the radiation of regular-sized engines with small-scale tests. To determine the similarity of plume radiation between reduced-scale rockets and regular-sized rockets in ground-test conditions, the flow and radiation of rocket engines in the geometric reduced-scale ratios of 0.1 to 1 are investigated in this study. First, a Calculate Fluid Dynamic (CFD) solver is used to obtain the flow field of the internal flow and plume. Thereafter, the Finite Volume Method (FVM) is applied to compute the 3D spectral-directed plume radiation in the 2- 6μm infrared waveband for the nonuniform absorptive/ emissive/scattering plume. The spectrum characteristics of gaseous compositions and Al₂O₃ particles are solved by using the weighted-sum-of-gray-gas (WSGG) model and Mie theory, respectively. Finally, the integral radiation on the surface of a high-temperature plume core (higher than 500K) that produces the volume radiation in different directions was investigated. The direction of the volume radiation is determined by the angle between the radiation direction and rocket axis. Our research shows that with the decreasing size of the rocket engine, the high-temperature core´s area decreases with the square order of the rocket size. The infrared spectral radiation of the plume also decreases with the square order. The infrared radiation of the gaseous components show a strong spectral difference, and the infrared radiation of the Al₂O₃ particles show the spectral property of a gray medium with the same temperature. The integrated infrared characteristics of the solid rocket plume mainly show the spectral continuity of Al₂O₃ particles, which decreases in the peak radiation spectrum of gaseous components. The emission and scattering of Al₂O₃ particles makes the plume radi- tion grow up remarkably, this phenomenon increases the plume radiation in the 4.2-4.45μm band to two times of the nonparticle radiation and increases the plume radiation in the 2.7-2.95μm band by 45%. The radiation intensity on the surface of the high temperature plume core increases with increasing sight angle.