Effect of frequency on mixing characteristics at the convergent nozzle in pulsed transverse jets

The exhaust plume of an aero engine is one of the main radiation sources of infrared detectors. Pulsed transverse jets were introduced into the exit of convergent nozzle to reduce the exhaust plume temperature. We performed numerical simulation to investigate the pulsation frequency effects on mixing performance improvement and the characteristics of vortexes. The introduction of pulsed transverse jets enhances the streamwise decay of exhaust plume and streamwise velocity attenuation progressively intensifying as the pulsation frequency decreases. At pulsation frequency f j = 20Hz, the high-temperature region in the exhaust plume has significantly altered and the pulsed transverse jets induce the temperature fluctuation near the nozzle exit downstream at f j = 100Hz. As the pulsation frequency decreases, the penetration depth of the counter-rotating vortex pairs induced by the pulsed transverse jets increases, and its entrainment effect becomes more pronounced. At pulsation frequency f j = 20Hz, the counter-rotating vortex pairs nearly fill the core region in the exhaust plume at Z/Dn = 3, entraining ambient fluid into the exhaust plume interior and enhancing exhaust plume mixing. The low-frequency jets significantly enhance turbulent fluctuation intensity within the shear layer of the exhaust plume and accelerating energy dissipation in the exhaust plume.