Objective  With the rapid development of advanced infrared detection technology and infrared tracking and striking technology, armed helicopters are increasingly threatened by infrared guided missiles from ground and air in the modern high-tech battlefield. In order to improve the battlefield survivability and combat assault capability of armed helicopters, advanced infrared stealth technology must be developed. The research shows that the use of shielding technology and the improvement of the ejector capacity of the suppressor have a significant effect on reducing the infrared radiation intensity of the exhaust system, but the specific technical means should depend on the structure of the infrared suppressor. For the diverter nozzle ejector infrared suppressor, limited to the size and shape of the helicopter, it is difficult to improve the ejector capacity of the diverter nozzle and reduce the exhaust and wall temperature in a limited space. Therefore, it is necessary to discuss the modification scheme of the diverter nozzle outlet to reduce the infrared radiation intensity of the diverter nozzle ejector infrared suppressor.

  Methods  A physical model was established including diverter nozzle, gas-collecting chamber, ejected gas inlet, curved mixing tube, covering shelter, and outer cover (Fig.1). The structured and unstructured hybrid grids were established, and the infrared radiation of the infrared suppressor was calculated by the forward-backward ray-tracing method. The calculation method is verified by experimental data (Tab.1-2,Fig.9). By comparing the pumping coefficient, total pressure recovery coefficient, outlet and wall temperature distribution of the mixing tube and infrared radiation intensity of the diverter nozzle ejector infrared suppressor (Fig.10-14), the effect of outlet structural parameters of diverter nozzle on infrared suppressor performance is analyzed from multiple perspectives.

  Results and Discussions   The experimental data are used to verify the calculation method. The pumping coefficient and total pressure recovery coefficient of the infrared suppressor under different diverter nozzle outlet structures are compared and analyzed (Fig.10). The exhaust temperature distribution of the mixing tube outlet plane of the infrared suppressor under different diverter nozzle outlet structures is shown (Fig.11). The temperature distribution of the outer mixing tube wall surface of the infrared suppressor under different diverter nozzle outlet structures is shown (Fig.12). And the infrared radiation intensity distribution of the infrared suppressor with different diverter nozzle outlet configurations on the horizontal and lead hammer detection surfaces in the 3-5 μm band (Fig.13) and 8-14 μm band is shown (Fig.14).

  Conclusions  Compared with the original model, the pumping coefficient of the Lobe_1 with a certain expansion angle is slightly reduced, the total pressure recovery coefficient of the Lobe_1 is reduced, and the peak exhaust temperature at the outlet of the intermediate mixing tube is reduced by 65.1 K. For Lobe_1, the wall temperature in the upper and lower areas of the mixing tube is reduced, but the temperature in the local area of the outer wall of the middle and rear sections of the mixing tube is increased. The lobed outlet structural (Lobe_2) with an outer expansion angle of 0 increases the pumping coefficient by 3.8%. The total pressure recovery coefficient is basically the same as that of the Lobe_1 model, and the peak exhaust temperature of the intermediate mixing tube is also reduced by 62.8 K, especially the effect of reducing the wall surface temperature of the mixing tube is the best. The outlet of the diverter nozzle with tab structure increases the pumping coefficient by 10.6%, but the total pressure recovery coefficient decreases 0.7%, and the average exhaust temperature of the inner mixing tube decreases by 19.3 K. Tab model has a poor effect on cooling the wall temperature of the mixing tube. In general, both lobe and tab structures play a role in ejection and mixing. In particular, the lobed outlet structure (Lobe_2) has the best effect on reducing the overall infrared radiation of the suppressor, and the infrared radiation intensity in the 3-5 μm band can be reduced by up to 21%, in the 8-14 μm band, the infrared radiation intensity can be reduced by 15%.