Study on the impact of APU inlet door angle on aerodynamic performance of inlet system

The Auxiliary Power Unit (APU) of civil aircraft primarily provides generator shaft power for the electrical system and bleed air for the air source system both on the ground and in the air. The APU inlet system draws airflow from outside the fuselage through inlet duct and ventilation cooling duct, supplying the APU with the required airflow under various operating conditions and ensuring proper ventilation and cooling of the compartment. The inlet system also aims to minimize pressure loss and inlet distortion at the APU's entrance. This study uses numerical simulation to study the impact of APU inlet door angle on aerodynamic performance of inlet system. The results show that within the study range, under the flight condition, the total pressure recovery coefficient and the ram recovery coefficient of the APU inlet duct outlet first increase and then decrease with increasing inlet door angle, reaching maximum values at door angle of 40°;under the ground condition, the total pressure recovery coefficient of the APU inlet duct outlet continuously increase with larger door angles;The inlet door angle has no significant regular impact on the magnitude of APU inlet distortion.