Research on Characteristics of Helicopter Engine Bleed Airflow Limitation and Temperature Drop
摘要
The helicopter’s environmental control system is restricted from drawing more than its engine’s maximum allowed bleed air volume to avoid excessive power loss. Considering the effects of flight attitude changes on bleed air parameters， this paper proposes the concept of “supercritical nozzle flow factor” and derives the corresponding calculation formula. Experimental data show that the deviation between the actual measured maximum bleed air volume of the engine and the theoretical calculation value is within 3%， validating the accuracy and practicality of this method for limiting engine bleed air flow. The method simplifies the testing process， avoids the interference of flow sensors on the characteristics of induced air flow， and enhances the test precision. Additionally， to reduce bleed air volume and eliminate safety hazards posed by high-temperature bleed air pipes to surrounding equipment， this paper improves insulation measures based on practical engineering and studies temperature drop characteristics under different bleed air temperature， pressure， and flow conditions at the outlet of the bleed air pipe and the outer surface of the insulation layer. These research results help optimize the bleed air pipe design， increase the thermal efficiency， and provide the technical reference for safe operation of helicopters.