Christian Behr

Progress in Efficient Active High-Lift

This paper presents some of the progress in research on efficient high-lift systems for future civil aircraft achieved by the Coordinated Research Centre CRC 880 sponsored by the German Research Foundation. Several new approaches to increasing the lift are applied as part of the design of a reference aircraft with short take-off and landing capability: The numerically predicted positive effect of Coanda jet blowing at the trailing edge flap is validated in water tunnel experiments. Robust miniature pressure and hot-fi�lm sensors are developed for the closed-loop control of a piezo-actuated blowing lip. A flexible leading-edge device utilizes composite materials, for which new structural designs are developed. Additionally, a potential de-icing system, as well as a lightning-strike protection are presented. A high power-density electrically driven compressor with a broad operating range is designed to provide the blowing air ow. Different propulsion systems for the reference aircraft are evaluated. An ultra-high bypass ratio engine is considered to be most promising, and thus a preliminary fan stage design process is established. The rotor dynamic influences of the engine on the aircraft structure are investigated through a hybrid approach using a multibody model and modal reduction.

MEMS pressure sensors embedded into fiber composite airfoils

The paper describes the integration of pressure sensors into fiber composite in order to obtain flow sensing airfoils to be used in future aircrafts. First, the sensor design and working principle is described, followed by an embedding procedure for damage-free integration. Here the sensors are faced to stresses by vacuum and curing during the embedding process into fiber-reinforced plastic. The mechanical characteristics and the influence of external mechanical stresses on the integrated sensor are further investigated. Finally, a sensor design unsusceptible to external mechanical stresses parallel to the surface of the airfoil is proposed and verified by tensile stress tests.

Structural integrated sensor and actuator systems for active flow control

An adaptive flow separation control system is designed and implemented as an essential part of a novel high-lift device for future aircraft. The system consists of MEMS pressure sensors to determine the flow conditions and adaptive lips to regulate the mass flow and the velocity of a wall near stream over the internally blown Coanda flap. By the oscillating lip the mass flow in the blowing slot changes dynamically, consequently the momentum exchange of the boundary layer over a high lift flap required mass flow can be reduced. These new compact and highly integrated systems provide a real-time monitoring and manipulation of the flow conditions. In this context the integration of pressure sensors into flow sensing airfoils of composite material is investigated. Mechanical and electrical properties of the integrated sensors are investigated under mechanical loads during tensile tests. The sensors contain a reference pressure chamber isolated to the ambient by a deformable membrane with integrated piezoresistors connected as a Wheatstone bridge, which outputs voltage signals depending on the ambient pressure. The composite material in which the sensors are embedded consists of 22 individual layers of unidirectional glass fiber reinforced plastic (GFRP) prepreg. The results of the experiments are used for adapting the design of the sensors and the layout of the laminate to ensure an optimized flux of force in highly loaded structures primarily for future aeronautical applications. It can be shown that the pressure sensor withstands the embedding process into fiber composites with full functional capability and predictable behavior under stress.

Active Flow Control via Piezo-Actuated Airfoils forHigh-Lift

This paper presents the development process of a dynamically actuated lip for active blowing at high-lift flaps. The system consists of MEMS pressure sensors to determine the flow conditions and adaptive lips to regulate the mass flow and the velocity of a wall near stream over the internally blown Coanda flap. By the oscillating lip the mass flow in the blowing slot changes dynamically, consequently the momentum exchange of the boundary layer over a high lift flap required mass flow can be reduced. In a first functional demonstrator piezo ceramic d33-stack actuators, operating at low voltage levels, are bonded to a metal substrate in a bending transducer configuration for basic experiments to determine the nominal displacement and the blocking force of the adaptive lip. Prospective all control systems shall be coupled to large-area sensor-actuator-arrays and integrated conformable into the structure. The efficiency increase of an internally blown Coanda flap by using unsteady blowing will be investigated during water channel tests which are in preparation. In this context an appropriate waterproof electrical insulation is evaluated by environmental tests. The first flow investigations will be implemented in a water tunnel in order to reduce the flow velocity and the system’s control frequency by a factor of 10 compared to a wind tunnel. Compared to the prior art, an expansion of the frequency range is expected and the benefits due to the compact and highly integrated design demand a high aerodynamic efficiency of this configuration.