Numerical Investigation of the Flow and Infrared Radiation Characteristics of Nozzles with Transverse Jets of Different Shapes

Abstract

The hot jet of an aero engine is one of the main radiation sources of infrared detectors in 3–5 microwave bands. Transverse jets were introduced into a hot jet to enhance mixing and reduce the infrared radiation characteristics. This proved to be a high-efficiency and low-resistance infrared suppression technology. The steady-state distribution of temperature data was simulated, which was needed in the thermal radiation calculation. The radiation characteristics were calculated based on the anti-Monte Carlo method in 3–5 microwave bands. The mechanics of enhanced mixing by a rectangular nozzle or transverse jets was investigated with the LES simulation. Compared with an axisymmetric nozzle, a rectangular nozzle induced abundant counter-rotating vortex pairs (CVP), hairpins, shears, and helical vortexes, which resulted in significant mixing enhancement and infrared radiation decrease of the hot jets. Further, circumferential transverse jets of different types were introduced downstream of the nozzle. These jets enhanced the mixing and reduced the infrared radiation in the 3–5 µm band. The mixing characteristics of these different schemes were studied in detail. Large-scale vortices formed on the windward portion of the hot jet boundary under the effect of the transverse jets, which caused strong CVP structures. They also resulted in hairpin vortexes, shear vortexes, and helical vortexes appearing earlier and occurring more frequently than with nozzles without transverse jets. The enhanced mixing caused by the transverse jets led to an increase in temperature decay and a decrease in infrared radiation in the 3–5 µm band. Further, transvers jets of different geometrical shapes (rectangular, cube, and circular schemes) achieved different mixing characteristics, and the rectangular transverse jets allowed the most significant mixing for the largest Q criterion value.

A Numerical Investigation of Film Cooling under the Effects of Different Adverse Pressure Gradients

“…The results showed that the wall temperature and infrared radiation could be effectively reduced via film cooling. Zhang et al [9] analyzed the suppression effect of cooling structures on the infrared radiation of nozzles by using the k-ω SST turbulence model, and they found that the film cooling slot had a better infrared suppression effect than the film cooling holes, but the flow loss of the film cooling slot was greater. Lu et al [10] conducted an experiment on the film cooling effect of the wall surface and central cone of a binary vectoring nozzle, and they found that the arrangement of the film holes had a great influence on the wall temperature.…”