Entrainment of air into an infrared suppression (IRS) device using circular and non-circular multiple nozzles

The present investigation predicts the mass entrainment into an IRS device which is used in naval or merchant ships. A high velocity jet emanating from the nozzle exit entrains ambient air to cool the hot combustion products of the gas turbines. Experiments have been carried out on a laboratory scale IRS device to measure the entrainment ratio. An optimum funnel overlap height (Hoverlap/Deq,nz = 0) has been found out from the experiments which shows the highest mass suction rate at that overlap height. Moreover, the entrainment is observed to increase with the inlet mass flow rate of the nozzle. For a full scale IRS device, the conservation equations for mass, momentum and turbulent kinetic energy as well as its dissipation rate are solved using finite volume techniques in a three-dimensional computational domain by employing eddy viscosity based k-ɛ turbulence model with standard wall function. The parameters such as the nozzle aspect ratio (AR), geometrical shape of the nozzles, pitch circle diameter (PCD) and multiple nozzles affect the entrainment ratio significantly. With five triangular nozzles (AR = 1), the entrainment rate is enhanced by 15.7% as compared to a single triangular nozzle (AR = 1).