Parametric Design, Comparison and Evaluation of Air Intake Types for Bleedless Aircraft

Kurzfassung

The development of aircraft in civil aviation has led to higher cruise flight altitude and Mach number. At the same time, economical and ecological requirements as well as comfort demands are increasing. This requires a new concept for the aircraft design, which may be the more electrical aircraft. In the proposed more electrical aircraft, all auxiliary systems are electric powered. This substitutes the pneumatic and hydraulic systems used in current aircrafts. The propulsion turbines of the next generation of aircraft will be designed for higher efficiency and durability. The bleed air outlets in a turbine decrease the efficiency and, by inducing vibrations on the blades, also significantly the durability of the engine. Moreover, the distribution of hydraulic fluid from the engine requires tubing throughout the aircraft, requiring fixed space and adding additional weight. Therefore, the increase in both efficiency and durability will be achieved by the electrification of the aircraft, which eliminates both bleed air and centralized hydraulic fluid distribution. In current aircraft, the bleed air is used partly to get compressed and warm air for the cabin air conditioning. In the next generation aircraft, the cabin air has to be provided by an air intake in combination with a compressor and an air conditioning system. The conventional centralized hydraulic system has to be replaced by electrical actuators or local hydraulic units. These components require also cooling air from the outside atmosphere, which has to be inducted by additional air intakes. Current civil transport aircraft commonly use NACA-type air intakes. The proposed new system design of the more electrical aircraft is characterized by the distribution of the consumers throughout the aircraft, which have to be cooled. This may require a wider variety of air intakes. Therefore a new design process including different types of air intakes has to be established. This work addresses the methods for the intake design process. One method to distinguish aerodynamic design methods is to categorize by the dimensions of the approach. One-dimensional approaches are most commonly used and combine streamline theory with empirical factors. They are used in preliminary design, as a relatively accurate estimation. In many cases, correction factors are used to extend the applicability of the method to describe the flow situation more realistically. Since empirical factors are used, the accuracy of these approaches is limited by the accuracy and portability of these factors usually obtained through experimental investigations. The objective of this work is to develop a method for preliminary air intake design. The focal point of the considerations is the intake design for supplying a compressor used in a civil transport aircraft at cruise flight condition at Mach0.82 and an altitude of 39000ft. Different intake types are investigated in order to identify an optimal configuration in terms of high pressure recovery as well as for low additional drag force on the aircraft. The main objective of the design process of the air intake is to maximize the total pressure recovery from the free-stream air in order to minimize the required compressor power.The method for preliminary intake design is supposed to be one-dimensional and applicable to various intake types. The effects of varying boundary layer thickness, mass flow rate, and flight altitude are taken into account. Furthermore, parameters that specify the geometry of the air intake are evaluated with regard to optimal performance. The chosen method is implemented into a software tool, which allows the calculation of different air intakes and the comparison of those with regard to the requirements. This new calculation tool allows for prediction of intake performance in an early design stage. Dependencies between total pressure recovery, drag, and mass flow of the different intake types are investigated.