Auxiliary Power Unit Compartment Design Optimization

Author(s): 
Jonathan Lewis, Gali Lazar, Ohad Gur (Israel Aerospace Industries)

In this paper a design process of auxiliary power unit (APU) compartment is presented. APU is an additional engine, used in air-vehicles development, which provides power to start the main engines, runs accessories while the engines are shut down and provides electrical and hydraulic power (depending on the design) before engine start (pre-flight tests, cabin ventilation, etc.). Reliability demands for APUs are quite high and its installation and operation should not interfere with the normal air-vehicle operation. Thus, its design incorporates several disciplines and models.

The design goal is to comply with the temperature level constraints, mass flow requirements, and reduce drag penalty to a minimum. The proposed method enables the cooperation of several stand-alone models, such as the inlet, APU-engine, 1-D flow and ejector and thermal model, which are integrated into a comprehensive design framework using the modeFRONTIER environment. The optimization of the APU compartment and inlet geometry were performed using a global search approach.

A bi-level design process was developed to enable minimum effort of updating the high fidelity model. Most of the design process is done using the low fidelity models, thus enabling a thorough study of the design space with low computer resources. Then, a validation process is conducted using the high fidelity model. The results prove the validity of the proposed method with reduction of the drag penalty and decreased temperature level below the required limits.