Numerical investigation of mixed convection through an infrared-suppression (IRS) device

Abstract

The flow through an infrared-suppression (IRS) device, installed on a warship, is often subject to various thermal regimes, including forced, natural, and mixed convection. When the ship becomes stationary/idle in the middle of a sea or in a port, mixed convection flow through the IRS device becomes noteworthy. In this paper, we numerically investigate the thermo-fluid characteristics through a cylindrical IRS device in mixed convection regime. Computations are performed for turbulent flow mixed convection with Richardson number in the range 0.1 ≤ Ri ≤ 10 to analyze the entrainment ratio (ER), flow field, and temperature variations in the IRS device. For a parametric study, dimensionless parameters such as nozzle-exit temperature, diameter ratio, nozzle protrusion, and funnel overlap are varied over the range of 1.91 ≤ T* ≤ 2.577, 1.05 ≤ DR ≤ 1.25, −1.5 ≤ NP ≤ 1.5, and − 22% ≤ OL ≤ 22% respectively. Temperature-dependent fluid properties are considered to obtain accurate results at higher temperature scales. The computed ER fairly agrees with the benchmark experimental results. With increase in Ri, the ER rises, whereas the actual mass suction diminishes. The centerline plume temperature at the exit of the IRS device is around 0.53 times the nozzle-exit temperature for Ri = 10, whereas it is almost identical at Ri = 0.1. The optimal Ri (=0.75) is obtained based on the maximum cooling efficiency. Finally, an empirical correlation for the ER is developed as a function of the above pertinent parameters.