Numerical Investigation of Air Entrainment and Outlet Temperature Characteristics of a ConvexType Infrared Suppression Device

Abstract

Infrared suppression devices (IRS) are frequently used in naval/cargo ships to passively entrain an additional amount of cold air from the atmosphere, and mix it with the hot plume so as to suppress its temperature, and the IR signature. In this work, a convextype IRS device has been proposed consisting of five numbers of the convextype funnels. The air entrainment ratio has been numerically computed by solving the transport equations (i.e., mass, momentum, energy, turbulent kinetic energy, and its dissipation rate in a structured grid arrangement by employing a pressurebased finite volume solver in ansysfluent. The pertinent parameters like the Reynolds number, inlet temperature ratio, convexradius ratio, and funneloverlap height have been varied in the range of −1.5 × 105 to 1.5 × 106, 1.243 to 2.576, 0.834 to 1, and 0 to 0.326, respectively. It has been observed that the air entrainment ratio increases with both the Reynolds number and convexradius ratio for the considered temperature ratios. An optimum convexradius ratio (=0.909) has been obtained, where the air entrainment and the outlet temperature become the maximum and the minimum, respectively. Both the inlet temperature ratio and overlap height significantly improve intake of cold air into the IRS device due to the additional buoyancy force, and the enhanced area availability for air the ingestion. The convextype IRS device performs better than a cylindricaltype IRS device. A nonlinear regression model based on the LevenbergMarquardt (LM) method has been deployed to develop a correlation equation for the air entrainment.