Estimation of Aerodynamic Loads on the APU Inlet Door in Civil Aircraft

The Auxiliary Power Unit (APU) of a civil aircraft provides essential air and power sources both on the ground and in-flight. The inlet system is responsible for supplying the APU with the necessary air for proper operation, and the aerodynamic loads are crucial design inputs for the APU inlet door structure and actuation system. This paper estimates the aerodynamic load on the APU inlet door using an engineering method and validates these estimates through Computational Fluid Dynamics (CFD) simulations. The results show that the aerodynamic load on the inlet door along the right boundary of the flight envelope does not change monotonically. Discrepancies between the engineering calculations and CFD results are likely due to variations in the CFD flow field, as well as differences in the velocity distribution and boundary layer thickness. Overall, the engineering method provides relatively conservative estimates of the aerodynamic load on the APU inlet door and is relatively accurate. During the preliminary design phase, this method can be used for rapid estimation of the aerodynamic load on the inlet door, offering a reference for swift iterations of the APU inlet door structure and actuation system designs.