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Flow sensor system for the separation detection at low speed in view of flight

Final Report Summary - FLOWSENSYS (Flow sensor system for the separation detection at low speed in view of flight)

Executive Summary:

The VISION 2020 for European aeronautics is a “greener” aircraft and responds directly to global climate change and the ever increasing need to stay competitive in a global market. Ambitious aims are presented in this document: The 2020 aircraft is quieter and cleaner. A 50% reduction in fuel consumption per passenger kilometre would lead to 50% fewer emissions of CO2. An 80% cut in NOx emissions would significantly reduce the impact of civil air traffic on global warming and the damage to the higher atmosphere. Besides environmental aspects, another important goal for the 2020 aircraft of the European air transport system is their capability of flying safely in all weather conditions and running on schedule 99% of the time. In order to meet this vision leaps in technological developments have to be made. One of the is the improvement of the high-lift performance of airliners. One approach is the avoidance of turbulent flow separation using active flow control (AFC). An aircraft with an AFC trailing edge flap could depart and approach using steeper trajectories. Furthermore, the takeoff and landing distances could be shorter and the noise nuisance at ground could be reduced. Other aspects are enhancing maximum takeoff weight, improving safety, and reducing complexity, weight, and dimensions of flap systems and thereby lowering the direct operating cost (DOC). Those improvements would be beneficial during cruise as well and a reduction of fuel consumption is possible under certain conditions. A modern active flow control system commonly consists of three components: an actuator device that is capable of stabilizing wall-bounded flows in order to delay or suppress flow separation, an intelligent control system to realize to ensure the effective and efficient use of the energy invested, and a fluidic sensor system identify the local state of flow.

The aim of FlowSenSys is to develop such an adequate sensor system, which operates in concert with an active flow control system, while providing robustness and high reliability.

In the first period of this project, various sensors were tested in different flow conditions with and without separation to examine their capability of identifying the flow condition on a generic flap at moderate Reynolds and Mach numbers. The measurements were performed at the end of the first project period. In the second period the focus was on the analysis of the data recorded to evaluate the sensor performance in light of their ability to detect flow separation. Within the third and final reporting period a complex outer wing model was equipped with the most suitable sensor type and wind tunnel experiments were performed in order to validate those sensors' performance under more realistic flow conditions. It was found that the EADS micro-dot surface hot film sensors are capable of detecting the state of flow by evaluating either the DC or the AC signal, which qualifies them to fulfill the requirements imposed on such a flow sensing system.

Project Context and Objectives:

The experimental analysis of flow separation in the boundary layer is an important aspect for the development of active flow control devices. On the one hand the highly sensitive fluidic sensors are necessary to investigate the flow phenomena during separation. On the other hand the sensors are a part of an active flow control system to allow for the adaptation of flow control parameters to the specific requirements of the flow conditions. For these applications the sensors need to be robust and sufficiently sensitive. Furthermore, when considering application on an airliner, their integration may not conflict with other design targets and maintenance procedures.

Aim of FlowSenSys was the selection and adaptation of suitable sensor concepts. Specific objectives were:

• Sensor concept development for separation detection towards application and integration in an aircraft
• Support of a system demonstration for active flow control system concept in closed loop architecture developed by SFWA partner EADS-IW; common application with an active flow control system on high-lift device.
• Wind tunnel demonstration of the sensor concept in realistic flow conditions together with SFWA partner EADS-IW

Those overall objectives translate into specific tasks. First, a review of available sensors was made to preselect those with the most promising characteristics. Parallel to that a new sensor layout was developed with special emphasis on the applicability of this concept in light of future industry application. Those sensor concept were then to be tested in generic and realistic flow conditions. Finally, a down selection of sensor concepts and designed was envisaged to be supplied to ongoing and future research projects.

Project Results:

Please see attached pdf document, as technical reporting without figures does not make much sense.

Potential Impact:

The experiments showed the feasibility of implementing an AFC sensor system for realistic flow conditions. The work conducted - in cooperation with SFWA partner EADS-IW - lead to deeper understanding of how such a system can be best designed for being applicable on a civil airliner and increased the available data basis for flow sensors in the light of flight application.

For this project the assumed business case was e.g. the replacement of a double slotted flap by a smaller single slotted flap. The AFC system for such an approach was researched and developed in the SFWA CfP projects AFCIN, FloCoSys, and DT-FA-AFC. Within this frame FlowSenSys can contribute to providing a sensing system to realize a closed-loop flow control architecture to achieve a more effective and efficient flow control authority. Besides a possible reduction of system weight, tipple down benefits are the reduction of the flap size (therefore freeing up additional space in the main wing element) and the reduction of maintenance costs (by reducing the system complexity compared to a double slotted flap).

The results of this project can serve as input for upcoming and ongoing projects. For further large scale testing or flight experiments an flow sensing system stands ready to be integrated.

List of Websites:

Prof. Dr.-Ing. Wolfgang Nitsche
Fachgebiet Aerodynamik, Sekr. F2, Technische Universität Berlin
Marchstrasse 12-14
10587 B e r l i n