Flow and heat transfer characteristics of a self-entraining ejector conical diffuser with and without slot guidance

Abstract

Self entraining diffusers are mechanical devices which are used to entrain ambient (cold) air to mix with the exhaust (hot) gases. These devices are commonly used at the rear of the gas turbine engines with the aim of cooling the exhaust gases without putting back pressure on the engine and in the process suppress the IR signatures. The performance of self entraining diffuser is critical when employed in helicopters and ships since the hot exhaust gases coming out of the gas turbines engines can be detected by infrared sensing missiles. The current study numerically investigates two conical self entraining diffusers, one with no slot guidance (conventional) and other with slot guidance while keeping all other geometrical parameters such as slot area, diffuser area ratio, diffuser angle, length of the diffuser, standoff distance, etc same. The simulation is carried out at fixed Reynolds number. The performance of the two self entraining diffuser is compared in terms of local and overall temperature drop, mass entrainment, pressure recovery and mixing. We find that the local temperature drop for slot guided diffuser is significantly high near the diffuser wall. The mass entrainment at each slot is also higher for guided slot. For slot guided diffuser, an additional peak in the velocity magnitude is seen due to the presence of guided slot which allow the primary flow in the diffuser to retain axial momentum over a larger distance. The overall temperature drop is higher for slot guided self entraining diffuser with improved pressure recovery.