Final Report Summary - ROBUSTAFC (Performance Evaluation of a highly robust Fluid Actuator for AFC)
Executive Summary:
Active flow control by means of pulsed blowing has proven to be effective and efficient to delay or avoid completely flow separation on aerodynamic bodies and therefore allows to increase their operating range. Such active flow control systems, however, require effective, efficient, and reliable flow control actuators. Preceding CfP projects within CS-SFWA (e.g. FloCoSys and DT-FA-AFC) provided the design and validation of a two-stage fluidic actuator, which generates pulsed air jets suitable for flow control applications without incorporating any moving or electrical components. This unique feature of fluidic components allows the design of extremely robust actuators, an overwhelmingly relevant aspect when considering the application of flow control technology in civil aviation. The project robustAFC aimed at furthering the TRL (Technology Readiness Level) of those actuator subsystems.
The approach to reach that aim was twofold: Extensive investigation of the internal flow field of those actuators allowed to increase the in-depth understanding of the switching mechanism inside the device and in consequence enabled the design of flow control actuators with superior performance. Concurrent work focused on the testing of actuator prototype samples in an simulated environment that is equivalent to the environment that the subsystem would encounter when integrated into an aircraft. Those tests where carried out on site at the SFWA consortium member INCAS and the extensively analyzed at TUB. Those experiments unveiled weaknesses in the original actuator design and allowed the formulation of recommendations for an improved concept leading to a flow control actuator that offers increased robustness and better aerodynamic performance.
Within the project the feasibility was proven to move the two-stage fluidic actuator up to TRL5.
Project Context and Objectives:
The overall goal of the Clean Sky Smart Fixed Wing Aircraft project is the development and implementation of active wing technology to reach the ACARE goals of the European Union. Those targets comprise a significant reduction of green house gases produced by air travel, a reduction of noise emissions and finally the increase of European competitiveness in the field of air transport.
As an aircraft spends most of its flight time in cruise, its wings are optimized for that part of the mission. Nevertheless, during take-off and landing, the wing needs to provide sufficient lift at low speeds and therefore requires a high-lift system, which is usually a complex combination of leading and trailing edge flaps. These components increase complexity and weight of the overall system and therefore increase the direct operating costs and fuel consumption. Active flow control on those devices enables the design of systems of less weight. In consequence, it directly contributes to reaching the ACARE goals described above. Such active flow control systems, however, require effective, efficient, and reliable flow control actuators. TUB has contributed to developing these actuator technologies in JTI-SFWA projects DT-FA-AFC and FloCoSys. Within the project reported here, the next step was taken to further the TRL level of the devised fluidic actuators by redesigning them with respect to enhanced robustness and putting them to test in the numerous harsh environment situations the AFC system would encounter when being implemented in practice.
The focus of the work was aimed at increasing the TRL of the proposed two-staged fluidic actuator systems, which provides pulsed air jets without incorporating moving or electrical components. To reach this aim the first step was to define a set of critical performance characteristics of the AFC subsystem with respect to flow control requirements. This was done in close cooperation with the SFWA consortium partners Airbus and EADS-IW (now: Airbus Group Innovations) as only those institutions could provide the required input from an industry perspective. After definition of the application requirements the specific test scenarios for the robust actuation subsystem were developed. As the results from those tests serve as a basis to evaluate the current TRL status of the technology, this work was again conducted in cooperation with Airbus and additionally with INCAS, the SFWA consortium member which has the capability to conduct harsh environment tests. In parallel, the two stage actuator system - developed in previous SWFA projects (e.g. DT-FA-AFC and FloCoSys) - was adapted for the current project. Prior to entering into harsh environment testing the subsystem was examined at TUB under normal lab conditions using imaging measurement techniques and extensive unsteady pressure measurements. The data gathered furthered the in-depth understanding of the internal flow characteristics of the AFC system, which is necessary to improve the design of the device. After processing and conditioning the recorded data, it was provided to INCAS to serve as reference data for the environmental testing. During the conduction of the harsh environment tests by INCAS TUB served in a consulting manner to analyze preliminary findings and to improve the supplied prototypes from sample to sample. Finally, the extensive test data recorded by INCAS was analyzed at TUB with respect to identifying critical failure modes. Based on that, additional recommendations were formulated and documented to improve the performance and durability of future fluidic actuator specimen of that type.
In the course of the project its design was modified to adapt it to problems and shortcomings observed in different stages of the testing.
Two different pathways of research were taken in this project to further the development of the flow control actuator technology:
A) In depth understanding of the internal flow physics of fluidic actuators:
This first pathway aimed at increasing the knowledge on the internal flow characteristics to enable the design of more efficient, more compact, and higher modulated flow control actuators. In addition, the information gained allow to understand the physical reasons for problems encountered in a more extreme environment. The tests were conducted and analyzed on site at TUB. Extensive simultaneous unsteady pressure measurements were undertaken und combined with PIV measurements to qualify and quantify the internal flow characteristics of the outlet stage actuator elements in order to being able to find the cause for possible underperformance at other than lab conditions.
B) Analysis of the effect of harsh environment conditions on the AFC system:
Within this pathway a two stage flow control actuator was evaluated with respect to its potential to withstand harsh environment conditions. The tests were conducted by INCAS, the project's partner for this pathway. Within the project the observations during testing in extreme environments were summarized (including the evaluation of disassembled prototypes after failure at TUB), the implications of specific observations were analyzed, and recommendations were given as to how the design should be modified to reduce or eliminate performance degradation. With progression of the projects many of those recommendations were integrated into the design of subsequent prototypes.
It is the authors opinion that the flow control hardware can be matured to TRL 5 without major hindrances, as all design modifications propositions formulated in the course of the project are viable. Additional testing might be required once a more specific application scenario is defined, which would in turn induce the conceptualization of more detailed actuator specifications.
Project Results:
Within the project robustAFC a two-stage fluidic actuator system for flow control applications was tested under normal and harsh environment conditions. The results were analyzed, their implications described, and recommendations formulated to improve the AFC system performance and robustness. As the scientific figures are essential for the presentation of the results, the reader is referred to the PDF document attached for a summary of the project's findings.
Potential Impact:
The experiments showed the feasibility of implementing an AFC system in an aircraft environment, although some issues remain to be solved. The work conducted - in cooperation with SFWA consortium member Airbus Group Innovation, Airbus, and INCAS - lead to deeper understanding where problems occur when integrating an AFC system into a civil aircraft, which solutions, e.g. for increasing the subsystems robustness against sanding, are the most promising, and provided experimental data to validate the novel two-stage fluidic actuator approach.
For this project the assumed business case was the one that was already considered in preceding projects such as AFCIN, DT-FA-AFC, and FloCoSys, which is the replacement of a double slotted flap by a smaller single slotted flap. 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 experiments within this project transitioned the research on flow control actuators from TRL 4 to TRL 5 testing and the results can serve as input for upcoming and ongoing projects. The results produced in robustAFC allows decision-makers in industry to evaluate the viability of flow control technology assess the issues that need to be addressed before considering this approach for e.g. flight testing.
List of Websites:
-
Active flow control by means of pulsed blowing has proven to be effective and efficient to delay or avoid completely flow separation on aerodynamic bodies and therefore allows to increase their operating range. Such active flow control systems, however, require effective, efficient, and reliable flow control actuators. Preceding CfP projects within CS-SFWA (e.g. FloCoSys and DT-FA-AFC) provided the design and validation of a two-stage fluidic actuator, which generates pulsed air jets suitable for flow control applications without incorporating any moving or electrical components. This unique feature of fluidic components allows the design of extremely robust actuators, an overwhelmingly relevant aspect when considering the application of flow control technology in civil aviation. The project robustAFC aimed at furthering the TRL (Technology Readiness Level) of those actuator subsystems.
The approach to reach that aim was twofold: Extensive investigation of the internal flow field of those actuators allowed to increase the in-depth understanding of the switching mechanism inside the device and in consequence enabled the design of flow control actuators with superior performance. Concurrent work focused on the testing of actuator prototype samples in an simulated environment that is equivalent to the environment that the subsystem would encounter when integrated into an aircraft. Those tests where carried out on site at the SFWA consortium member INCAS and the extensively analyzed at TUB. Those experiments unveiled weaknesses in the original actuator design and allowed the formulation of recommendations for an improved concept leading to a flow control actuator that offers increased robustness and better aerodynamic performance.
Within the project the feasibility was proven to move the two-stage fluidic actuator up to TRL5.
Project Context and Objectives:
The overall goal of the Clean Sky Smart Fixed Wing Aircraft project is the development and implementation of active wing technology to reach the ACARE goals of the European Union. Those targets comprise a significant reduction of green house gases produced by air travel, a reduction of noise emissions and finally the increase of European competitiveness in the field of air transport.
As an aircraft spends most of its flight time in cruise, its wings are optimized for that part of the mission. Nevertheless, during take-off and landing, the wing needs to provide sufficient lift at low speeds and therefore requires a high-lift system, which is usually a complex combination of leading and trailing edge flaps. These components increase complexity and weight of the overall system and therefore increase the direct operating costs and fuel consumption. Active flow control on those devices enables the design of systems of less weight. In consequence, it directly contributes to reaching the ACARE goals described above. Such active flow control systems, however, require effective, efficient, and reliable flow control actuators. TUB has contributed to developing these actuator technologies in JTI-SFWA projects DT-FA-AFC and FloCoSys. Within the project reported here, the next step was taken to further the TRL level of the devised fluidic actuators by redesigning them with respect to enhanced robustness and putting them to test in the numerous harsh environment situations the AFC system would encounter when being implemented in practice.
The focus of the work was aimed at increasing the TRL of the proposed two-staged fluidic actuator systems, which provides pulsed air jets without incorporating moving or electrical components. To reach this aim the first step was to define a set of critical performance characteristics of the AFC subsystem with respect to flow control requirements. This was done in close cooperation with the SFWA consortium partners Airbus and EADS-IW (now: Airbus Group Innovations) as only those institutions could provide the required input from an industry perspective. After definition of the application requirements the specific test scenarios for the robust actuation subsystem were developed. As the results from those tests serve as a basis to evaluate the current TRL status of the technology, this work was again conducted in cooperation with Airbus and additionally with INCAS, the SFWA consortium member which has the capability to conduct harsh environment tests. In parallel, the two stage actuator system - developed in previous SWFA projects (e.g. DT-FA-AFC and FloCoSys) - was adapted for the current project. Prior to entering into harsh environment testing the subsystem was examined at TUB under normal lab conditions using imaging measurement techniques and extensive unsteady pressure measurements. The data gathered furthered the in-depth understanding of the internal flow characteristics of the AFC system, which is necessary to improve the design of the device. After processing and conditioning the recorded data, it was provided to INCAS to serve as reference data for the environmental testing. During the conduction of the harsh environment tests by INCAS TUB served in a consulting manner to analyze preliminary findings and to improve the supplied prototypes from sample to sample. Finally, the extensive test data recorded by INCAS was analyzed at TUB with respect to identifying critical failure modes. Based on that, additional recommendations were formulated and documented to improve the performance and durability of future fluidic actuator specimen of that type.
In the course of the project its design was modified to adapt it to problems and shortcomings observed in different stages of the testing.
Two different pathways of research were taken in this project to further the development of the flow control actuator technology:
A) In depth understanding of the internal flow physics of fluidic actuators:
This first pathway aimed at increasing the knowledge on the internal flow characteristics to enable the design of more efficient, more compact, and higher modulated flow control actuators. In addition, the information gained allow to understand the physical reasons for problems encountered in a more extreme environment. The tests were conducted and analyzed on site at TUB. Extensive simultaneous unsteady pressure measurements were undertaken und combined with PIV measurements to qualify and quantify the internal flow characteristics of the outlet stage actuator elements in order to being able to find the cause for possible underperformance at other than lab conditions.
B) Analysis of the effect of harsh environment conditions on the AFC system:
Within this pathway a two stage flow control actuator was evaluated with respect to its potential to withstand harsh environment conditions. The tests were conducted by INCAS, the project's partner for this pathway. Within the project the observations during testing in extreme environments were summarized (including the evaluation of disassembled prototypes after failure at TUB), the implications of specific observations were analyzed, and recommendations were given as to how the design should be modified to reduce or eliminate performance degradation. With progression of the projects many of those recommendations were integrated into the design of subsequent prototypes.
It is the authors opinion that the flow control hardware can be matured to TRL 5 without major hindrances, as all design modifications propositions formulated in the course of the project are viable. Additional testing might be required once a more specific application scenario is defined, which would in turn induce the conceptualization of more detailed actuator specifications.
Project Results:
Within the project robustAFC a two-stage fluidic actuator system for flow control applications was tested under normal and harsh environment conditions. The results were analyzed, their implications described, and recommendations formulated to improve the AFC system performance and robustness. As the scientific figures are essential for the presentation of the results, the reader is referred to the PDF document attached for a summary of the project's findings.
Potential Impact:
The experiments showed the feasibility of implementing an AFC system in an aircraft environment, although some issues remain to be solved. The work conducted - in cooperation with SFWA consortium member Airbus Group Innovation, Airbus, and INCAS - lead to deeper understanding where problems occur when integrating an AFC system into a civil aircraft, which solutions, e.g. for increasing the subsystems robustness against sanding, are the most promising, and provided experimental data to validate the novel two-stage fluidic actuator approach.
For this project the assumed business case was the one that was already considered in preceding projects such as AFCIN, DT-FA-AFC, and FloCoSys, which is the replacement of a double slotted flap by a smaller single slotted flap. 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 experiments within this project transitioned the research on flow control actuators from TRL 4 to TRL 5 testing and the results can serve as input for upcoming and ongoing projects. The results produced in robustAFC allows decision-makers in industry to evaluate the viability of flow control technology assess the issues that need to be addressed before considering this approach for e.g. flight testing.
List of Websites:
-
