Effect of diffuser angle and perforations on the performance of an infrared-suppression (IRS) device under mixed convection

Abstract

The flow within an infrared suppression (IRS) device installed on a warship operates under varying thermal regimes, including forced, natural, and mixed convection. While the effects of geometric modifications to the IRS devices have been extensively studied in forced and natural convection scenarios, their influence in the mixed convection regime remains poorly understood. This study examines the performance of four distinct IRS device configurations—converging, straight, diverging, and a perforated-diverging design under mixed convection conditions for Richardson numbers (Ri) ranging from 0.1 to 10. Numerical simulations are performed to analyze fluid flow and thermal fields, entrainment ratio (ER), exit temperature, pressure recovery coefficient (C_PR), and cooling efficiency (η), considering diffuser angles (−5° to +5°) and perforated diffuser rings. The findings reveal that diverging (positive) diffuser angles enhance thermal suppression and achieve higher entrainment ratios compared to converging (negative) diffuser angles in the mixed convection regime. Specifically, varying the diffuser angle from −5° to +5° leads to a notable increase in the entrainment ratio (ER), with improvements of 67 %, 41 %, and 37 % observed at Richardson numbers (Ri) of 0.1, 1, and 10, respectively. Additionally, the perforated-diverging configuration consistently outperformed all other configurations, achieving the highest ER and superior thermal suppression across all Ri. It enhanced the ER by 1.78 times at Ri = 0.1 and 1.4 times at Ri = 10 compared to the converging design, and exceeded the diverging design by 7 % and 2.8 % at Ri = 0.1 and 10, respectively. The results presented in this study contribute to a deeper understanding of IRS design optimization and effective infrared signature mitigation for application in the industrial and defense sectors.