Inline-Slot Ejector Diffuser for a Warship to Suppress IR Signatures

Abstract

The infrared (IR) signatures emitted by warships can substantially reduce the survivability chances while operating in the enemy area, as these signatures can be tracked and locked-on by the heat seeking missiles. The primary source for the IR signatures in a warship is the gases emanating from the exhaust of the gas turbine engine. These signatures can be suppressed by installing the passive infrared suppressors such as ejector diffusers, downstream of the turbine exhaust. The prime objective of an ejector diffuser is to reduce the exhaust gases temperature with minimal back pressure. In the present investigation, inline-slot conical ejector diffuser is numerically studied. From the open literature it is found that only step-slot ejector diffuser has been explored and no work on the inline-slot ejector diffuser is reported. Preliminary investigations on the inline-slot ejector diffuser show the performance to be better in terms of mass entrainment and static pressure recovery than the step-slot ejector diffuser, which is commonly used with warship power plants. The focus of the present study is to establish the effect of nozzle exit conditions (i) inlet swirl (S), and (ii) inlet turbulence intensity (TI) on the performance of inline-slot ejector diffuser. In the first part, inlet swirl is varied in the range 0≤S≤0.3 in step of 0.05, and in the second part TI is varied in the range of 1%≤TI≤15% in step of 3%. The performance is evaluated in terms of local and cumulative mass entrainment ratios, non-dimensional temperature distribution, and static pressure recovery. For the first part, it is seen that there is 3% drop in cumulative mass entrainment with the increase in swirl number from 0 to 0.3 and this can be attributed to the drop in potential core region. Higher wall temperatures in the mixing tube are observed for all the configurations with swirl cases. Static pressure recovery increases with the increase in the swirl number. For the second part, the effect of turbulence intensity on the performance of inline slot ejector diffuser is carried out. It is seen that the mass entrainment decreases by ~5% when turbulence intensity is increased from 1% to 15%. No significant effect of turbulence intensity is seen on the temperature distribution and pressure recovery.