Active Flow Control Technique on Trailing Edge Shroud for Improved High Lift Configurations

Final Report Summary - ATTESI (Active Flow Control Technique on Trailing Edge Shroud for Improved High Lift Configurations)

Executive Summary:

"ATTESI" aimed at developing methods of active flow control for drooped spoiler configurations in order to achieve larger maximum lift coefficients.

Modern aircraft such as the A350 use so-called drooped spoiler configurations in combination with a relatively simple single-hinge flap, since this system allows a significant simplification of the flap driving mechanism and thus reduced weight. The drooped spoiler is needed to control the gap between the main wing and the flap. Since drooping the spoiler increases the local camber and introduces a "kink", the flow along the spoiler is prone to separation and therefore the drooped spoiler air foil in itself has a similar, but not significant larger high-lift potential as compared to more conventional solutions.

The objective of "ATTESI" is to apply methods of active flow control as well as a smart surface to such a configuration to increase the high-lift potential. To do so, possible separation along the spoiler is influenced by local fluidic devices (vortex generator jets, VGJs), this allows larger droop and, thus, more camber and higher lift. The kink that exists near the spoiler hinge line, and which becomes significant, especially if larger droop is to be applied, is smoothed by a local smart surface using an elastic "cogs-panel". Furthermore, to increase the total benefit a second fluidic device, the "fluidic gurney", FG, is applied to the trailing edge of the main element.

For such an air foil, the benefit of the flow control methods is very closely coupled to the configuration of the flap and the spoiler. To bring out the full potential it is essential to design specific configurations by numerical optimization, taking into account the beneficial effect of the flow control. While the FG can be included in design/optimization computations relatively straightforward, the VGJs create a local 3D structure being orders of magnitude smaller than the chord, hence they cannot be resolved without massive numerical effort. Therefore, to include the VGJs in design computations, a special "statistical" model was developed, which accounts for a certain additional shear stresses generated from the VGJs and implements them into standard-2D-RANS-design computations.

The resulting, optimized settings of spoiler droop and flap along with specific settings of the flow control methods were then tested in a low speed wind tunnel test.

Project Context and Objectives:

The CfP-project “ATTESI” is part of WP1.1.4 within the CleanSky / Smart Fixed Wing program. The key points requested in the call fiche are:

• Design, experimental and numerical validation of active flow control (AFC) on trailing edge shroud for improved high-lift configurations
• Slatless high-lift configuration with drooped spoiler; integration of active flow control at the kink and at the spoiler trailing edge
• Development of a structural concept that minimizes the kink by, e.g. “smart structure”

In the ATTESI description of work, the active flow control device on the spoiler trailing edge is a “fluidic gurney” – a fluidic jet emanating at the spoiler trailing edge in downward direction more-or-less normal to the chord line. Such device is similar to mechanical gurney flaps, which are well known to increase lift. As an active flow control device at the spoiler kink the “vortex generator jets” were chosen. They energize the local boundary layer and are able to reduce the detrimental aerodynamic effect of the kink on the local flow. These general ideas were compiled into an approach with three work packages:

Work package 1 developed a structural concept that enables a drooped spoiler with a smooth contour. The concept allows for reasonably high spoiler droop angles (where “droop” is downward, e.g. increases the camber of the ai rfoil), while still retaining the capability to use the spoiler as an air brake device (upward deflection). WP1 was led by IBK Nuremberg. More specifically, the objectives were:

• Participate in discussion of detailed concept by performing a thorough literature review of drooped spoiler concepts with smooth contours
• Build model representations (FEM) of spoiler surfaces for different concepts in order to assess the general behaviour
• Elaborate a detailed concept for spoiler droop with smooth contour
• Design, manufacture and test the concept on demonstrator level

Work package 2 performed numerical evaluations and optimization of the air foil, including spoiler droop and AFC. The aerodynamic setup has several different design variables: flap setting (3 variables: gap, overlap, angle), spoiler droop angle, setup and position of both AFC devices as well as amplitude of the fluidic forcing (e.g. mass-flow). Therefore, only a numerical optimization procedure indentifies the potential effectiveness and efficiency. WP2 was led by FOI Stockholm. More specifically, the objectives were:

• Build up an optimization setup for fully automated numerical optimization, using suitable numerical methods, optimization algorithms as well as a meaningful cost function
• Validate the numerical representation with experimental data (from WP3/background knowledge) and validate a 2D-RANS-approach for the representation of the VGJs (“statistical VGJ model”) by 3D computations of fully resolved VGJs.
• Run various optimizations with the validated tools and models.

Work package 3 was responsible to accumulate the results into an experimental setup in the laboratory scale wind tunnel “MUB” in Braunschweig. WP3 was led by TU-BS. More specifically, the objectives were:

• Participate in discussion of the concept by contributing with background knowledge on active flow control devices; Deliver and discuss experimental data for validation work in WP2
• Design and manufacture a suitable air foil model that allows representation of the spoiler droop and has the two AFC-systems integrated.
• Perform windtunnel tests in the wind tunnel “MUB”
• Analyse and compare the wind tunnel data to the numerical data from WP2

Project Results:

See attached pdf D43_FinalReport.pdf, which is equivalent to the deliverable D4.3

Potential Impact:

Impact

Active flow control and - more specific - suppression of turbulent separation is a key enabler to meet the challenges of future air transport systems. Future aircraft with innovative high-lift systems are expected to be lighter, more efficient, less noisy, easier in maintenance and will probably utilize synergies on aircraft level, e.g. between a system of active flow control as a high-lift device and a system for hybrid laminar flow. Extensive research on future technologies such as active flow control is thus crucial to keep the European aircraft industry up to date with global challengers.

In the CfP-project "ATTESI" a design method for drooped spoiler airfoil configurations was developed, that allows a specific "design to flow control" by taking the effect of the flow control method into account already during design computations. This is achieved by means of a so-called statistical vortex model. The design computations allow to quantify the total potential and efficiency of such flow control system of the use with drooped spoilers. Furthermore, a smart surface, based on an elastic cogs panel, was developed that allows to smoothen the kink that would otherwise exist if a spoiler is lowered extensively.

Dissemination

Dissemination is based on the SFWA work package meetings, conference presentations, paper publications along with the dissemination of the deliverables within the SFWA-consortium.

Within WP1.1.4 regular meetings (approximately half-year basis) have been held and the coordinator of ATTESI attended all these meetings, giving a technical presentation about the project status and including an intensive discussion of technical details.

Oral conference presentations and accompanying papers are summarized in the respective list.

Exploitation

Since ATTESI is a CfP project in SFWA, exploitation is ensured by the close connection and monitoring of the project results by the SFWA consortium.

Contact via coordinator:

Dr.-Ing. Peter Scholz

P.Scholz@tu-braunschweig.de

+49 531 391 94256