Numerical Investigation of Air Entrainment and Outlet Temperature Characteristics of a Convex-Type Infrared Suppression Device

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 convex-type IRS device has been proposed consisting of five numbers of the convex-type 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 pressure-based finite volume solver in ansysfluent. The pertinent parameters like the Reynolds number, inlet temperature ratio, convex-radius ratio, and funnel-overlap 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 convex-radius ratio for the considered temperature ratios. An optimum convex-radius 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 convex-type IRS device performs better than a cylindrical-type IRS device. A nonlinear regression model based on the Levenberg-Marquardt (L-M) method has been deployed to develop a correlation equation for the air entrainment.