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COMbined Passive and Active Flow Control Technology Wing

Periodic Reporting for period 1 - COMPACT (COMbined Passive and Active Flow Control Technology Wing)

Reporting period: 2019-05-01 to 2020-04-30

A key goal of ACARE and H2020 is the reduction in fuel burn for civil aircraft, leading to reduced environment impact through reduced emissions, both CO2 and NOx. This can be achieved in part by reducing the drag of the aircraft by maintaining laminar flow over a significant extent of the wetted surface. The are two principal ways to do this: Natural Laminar Flow (NLF) and Hybrid Laminar Flow Control (HLFC). The former is achieved through aerodynamic shaping and the latter through a combination of aerodynamic shaping and boundary layer control.
The aim of this project is to design and manufacture a large HLFC half model, representative of a civil transport aircraft wing, for installation in the ONERA S1MA tunnel. The model will be capable of testing the effectiveness of laminar flow control devices at transonic speeds (M~0.85) and high Reynolds number (>10 million/m).
The model will incorporate systems for delaying transition in the leading edge region in two spanwise sections. The outer section will address the HLFC requirements, with active suction through the surface of the porous wing leading edge. The wing will incorporate pipework permitting suction to be applied through the porous surface using a suction source provided by the wind tunnel operator. The location of boundary layer transition across the span will be measured in the experiment using the IR technique and the upper wing surface will therefore include an insulating material for the measurement of transition using IR thermography. As with all HLFC models, the surface finish will be very high quality with no steps or gaps. The suction system and instrumentation will be fully tested prior to delivery of the model. The inboard part of the wing will be equipped with both passive and active (wall suction) anti-contamination devices to investigate ways to control attachment line transition. The model will be fitted with a range of instrumentation including pressure tappings, unsteady pressure transducers, accelerometers, strain gauges and possibly hot films, all of which will be thoroughly tested during final assembly. Finally, on completion of the model assembly, the model deformation due to representative applied static loads will be measured.
Significant work on the project has been delayed for almost one year, primarily due to delays in other projects within the relevant CS2 LPA Work Package which are related to the aerodynamic design of the wing. Preliminary geometry was supplied in February 2020, but this was not confirmed as the final geometry until April 2020. Hence, the work performed has only address the requirements capture and geometric specification phase of the project.
The main technically ambitious parts required in COMPACT can be summarized by the following opportunities for innovation, each one challenging and representing a step beyond the state-of-the-art in WT models design and manufacturing.
• Although ARA has experience in applying insulating panels with high emissivity, for IR thermography on models designed for the ARA TWT, COMPACT will allow the development of techniques for incorporating these onto significantly larger models. This will involve developing machining techniques and finishing methodologies to maintain tolerance and roughness requirements.
• Designing the active and passive suction chambers will require advancing the state-of-the-art for model design. ARA will build on its expertise gained in UK research projects to achieve this through a combination of numerical simulation of the internal flow using CFD and structural analysis using FEA.
• In recent years ARA has developed proficiency with a model deformation measurement (MDM) technique known as ‘digital image correlation’. This method relies on two cameras installed in a stereo configuration imaging a random-pattern-covered model surface in a loaded and unloaded condition and using photogrammetry and cross-correlation to calculate the 3D surface shape and deformation. The system has been used successfully in the ARA facility for both static and dynamic deformation measurements. COMPACT will enable the technique to be extended to large models during the static load ground test.
• A remotely controlled device for simulating steps and gaps representative of those likely on full-scale aircraft will be developed as part of COMPACT. This has been achieved previously using replaceable segments, so an innovative approach will need to be taken to enable the device to be remotely operated.
Apart from the points discussed above, another important aspect will be the support to the WT test campaign performed by the TM, positioning the COMPACT project at a very high level in the landscape of research projects investigating HFLC capabilities in transonic conditions. The scope of the test is quite ambitious; it aims at demonstrating the aerodynamic efficiency and the robustness of active and passive HLFC technologies under transonic flow conditions.
Through the successful implementation of the COMPACT project, new concepts and improved technologies for a more reliable HLFC will be validated, for the enhanced performance and competitiveness of next generation aircraft.
HLFC model installed in the ARA TWT