Theoretical and experimental analysis of overall cooling effectiveness for afterburner double-wall heat shield

Abstract

The porous heat shield installed in the afterburner can effectively prevent the afterburner cylinder from overheating. Impingement/effusion cooling is one composite cooling technique to effectively improve the overall cooling effectiveness of the heat shield. Designing effective and efficient double-wall configurations requires a detailed understanding of how geometry and operating conditions affect the way coolant cools the afterburner cylinder. In this study, conjugated heat transfer experiments were conducted using IR thermography for double-wall heat shields with three open areas of the impingement plate (σ = 0.5%, 0.7%, 0.8%). The momentum flux ratio was varied in the range 0.01≤I≤0.50. The mainstream Reynolds number, based on the diameter of the film hole, was varied in the range 800≤Reg≤2000. The effects of geometrical and aerodynamic parameters on overall cooling effectiveness were experimentally and numerically investigated with the comprehensive effects of solid heat conduction and convection heat transfer. The experiments were modeled in a low-temperature state (Tg = 603 K, Tc = 298 K), which was based on the analogy theory and matching principle, as if the experiments were conducted under engine operating conditions. The modeling accuracy of experimental results was analyzed by the analogy theory. Results show that the difference in the overall cooling effectiveness between “laboratory” conditions (Tg/Tc = 2) and “engine” conditions (Tg/Tc = 4) is within 0.048. The overall cooling effectiveness is mainly affected by the open area through adiabatic cooling effectiveness and internal heat transfer, and that is mainly affected by the mainstream Reynolds number through external heat transfer. According to the area-averaged results in given experimental conditions, the maximum overall cooling effectiveness raise and drop coefficients after increasing open area and mainstream Reynolds number are 17.3% and 6%, respectively. Thus, the high open area and low mainstream Reynolds number are beneficial to improve the overall cooling effectiveness of the afterburner double-wall heat shield. Furthermore, the experimental measurements provide an important database for the evaluation of computational fluid dynamics simulations of the conjugate heat transfer effects occurring in the double-wall heat shield.