Flows in aircrafts air supply systems

Department Fluid Systems

A major change in the design of future civil transport aircraft will be the high level of electrification of nearly all systems and sub-systems. The new architecture will significantly reduce weight replacing heavy bleed air, pneumatic and hydraulic ducting by a new electrical power supply system. This electrical system will be used to generate pneumatic or hydraulic power locally in the vicinity of the consumer. In the particular case of the environmental control system there will be no bleed air anymore diverged from the engines. Hence, new air intakes are inevitable to support the climate packs with fresh air. Furthermore, new requirements in regard to mass flow rate and pressure recovery for the air intake itself and to the overall performance of the aircraft have to be fulfilled.
Even in the early aircraft design phase it is necessary to be able to determine the shape design of the air intake for the typical flight conditions and determine consumer needs. A new one-dimensional (1D) air intake design tool, called AIcom, has been developed to provide reasonable geometrical input data for air intake shape design and to cover a whole range of flight conditions for required mass flow rates and pressure recoveries. Based on given free stream conditions the tool provides a good estimate of the geometry and the performance for three air intake types, scoop, rectangular and NACA inlets.
Originally the first version of the 1D design tool was restricted to a given fixed input parameter set, i.e. Mach number, ambient pressure and density and a predefined boundary layer thickness. Now the latest version of AIcom is directly coupled with flow simulation data (CFD) used as input parameters for the design process. Based on local flow field data a point-wise intake design can be conducted for the whole aircraft surface. For each location on the surface an optimized intake with regard to pressure recovery, additional drag counts, weight and other characteristics can be proposed.
Since the new coupled approach yields only a proposal for an air intake design, more detailed design studies have to be conducted for certain locations in order to improve the performance of the intake itself and the global performance of the aircraft. Here, CFD studies allow for a multi-point optimization of the intake – aircraft integration, whereas consumers like heat exchangers or turbo compressors also have to be considered.



Fig. 1: Colored surface contours of the predicted drag count of a NACA-air inlet for each point of the airplane's surface.



Fig. 2: Pressure contour along the side-walls of a NACA- air inlet with subsequent diffusor and a heat exchanger as consumer calculated with CFD.

Prof. Dr.-Ing. Claus Wagner
German Aerospace Center

Institute of Aerodynamics and Flow Technology
, Fluid Systems
Tel: +49 551 709-2261

Fax: +49 551 709-2241

E-Mail: Claus.Wagner@dlr.de
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