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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - FLOWCAASH (FLOW Control Actuators at Aircraft scale manufacturing by SLM with high aerodynamic performance for using in Harsh environment)

Teaser

Summary

The aerospace industry has a need for engine with more ecologic and economic aspects that the current ones. In order to attain these aspects higher Bypass Ratio (BR) and lower Fan Pressure Ratios (FPR) are found. Very High Bypass Ratio (VHBR) and Ultra High Bypass Ratio (UHBR) are optimized engines to ensure these ratios. UHBR engines have lower CO2 and NOx emissions, higher efficiency and lower fuel consumption. The integration of VHBR engines under the wing of conventional aircraft is challenging but it is more when regarding to UHBR engines in novel aircraft because the nacelle of these engines is larger than VHBR ones. Consequently, it is more difficult to guarantee enough clearance between the nacelle and the runway surface. UHBR engines should be more closely-coupled to the wing to avoid larger landing gear struts suffering from weight and space drawbacks and to prevent the increase of landing gear noise. This leads to a larger slat cut-out in the wing-nacelle junction to prevent collisions of the deployed slat with the nacelle. There is another challenge to be faced, local flow separations, which emerge at high angle of attack and low speeds in the internal region between wing and nacelle. The larger slat cut-out enhances the risk of these separations, called nacelle-wake separation. This separation reduces the maximum achievable lift and induces wing stall. Currently, the application of nacelle strakes to prevent or attenuate the influence of nacelle-wake separation in aircrafts, which present smaller engine nacelles under wing, is successful. These nacelle strakes are delta shaped panel sheets located at the nacelle which trigger a longitudinal vortex which supports the mixing of the flow downstream of the slat cut-out and increase the maximum lift of the aircraft. However, the use of the nacelle strake will be insufficient to recover the lift loss due to the slat cut-back. To overcome this problem, the use of Active Flow Control (AFC) to actively suppress the local flow separation is proposed. AFC can increase the kinetic energy of the boundary layer downstream of the slat cutout to avoid the nacelle-wake separation. AFC has the potential of delaying local separation to higher angles of attack and increasing maximum lift. Actuators need to be installed in restricted spaces and with complex geometry. Conventional manufacturing technologies present important limitations. SLM emerges as a potential manufacturing process since it can develop innovative design concepts, enables a geometric freedom and combining with topology optimization lightweight structures with improved performance can be achieved. The main goal of FLOWCAASH is to design and manufacture reliable and safe flow control actuators at aircraft scale by SLM able to withstand the high temperatures and pressures during flight test, aerodynamic performance and high resistance to harsh environments. Two types of actuators have been considered, Pulsed Jet Actuators (PJA) and Steady Blowing Actuators (SBA), satisfying aerodynamic requirements for which shape accuracy and surface roughness have been strictly controlled. Resistance to harsh environment including rain, icing, sand and dust, vibrations and anti-icing fluid is an additional requirement for the innovative flow control actuators.

Work performed

The design of SBA and PJA was developed starting from the geometry with optimized mass flow. Designs were optimized based on the distortion prediction simulation results and dimensional measurements. The optimization of the designs led to minimized dimensional deviations. Design rules were determined for Ti6Al4V and SLM technology and were implemented in the designs. Ti6Al4V powder was characterized to verify its usefulness for SLM process. Powder morphology, particle size distribution, humidity, internal porosity and flowability were determined. Processing parameters were also optimized to guarantee a defect free material. Employing the optimized processing parameters, SBA and PJA actuators were manufactured by SLM, three actuators of each type. None of the actuators presented cracks and the dimensional deviations and defects observed in the first manufactured actuators were improved in the subsequent actuators by geometry changes of critical parts and by the optimization of the supporting strategy. The manufactured actuators were post-processed subjecting them to a heat and surface treatment to release the stresses generated during the SLM process and to achieve an adequate combination of mechanical properties to ensure a suitable behavior during the tests (vibrations tests) and to reduce the roughness achieved in as-built condition. In general, the heat treatment increased slightly the dimensional deviations but were considered acceptable to perform aerodynamic and harsh environment tests. The reproducibility verification was also assessed to demonstrate that the process is stable and repeatable. For that, several control samples were manufactured such as a cube, tensile sample and a powder capsule. These control samples were characterized in terms of density, microstructure, hardness, mechanical properties and oxygen content of the powder retained in the capsule. It was concluded that the SLM process is reproducible. The recycled powder was also analyzed. It was verified that the powder properties do not get degraded significantly. The designing of the equipment and the definition of the testing conditions were carried out. A test bench was designed for aerodynamic testing to record the air flow characteristics at the actuators inlet in terms of mass flow and pressure, and the air flow speed around the whole actuators outlet. In the case of harsh environment tests, the procedures were defined. In addition, a climatic chamber was adapted to perform icing and de-icing fluid tests and another dedicated test chamber was developed for sand and dust tests. Moreover, a test bench was developed to perform rain tests. Finally, different test fixtures were designed in order to fix actuators to the shakers during vibration tests.

Final results

FLOWCAASH aims at developing innovative and complex designs of Flow Control Actuators to be installed in restricted spaces and to be manufactured by SLM, since the improved designs are not feasible to manufacture by conventional technologies. The use of SLM will contribute to make advance of the lightweight, complexity and design freedom possibilities. During the project it will be demonstrated that the developed actuators have a high aerodynamic behavior and they assure a safe operation under harsh environment conditions. The main outcomes (foreground) of the project were identified as innovative methodologies and results to support the industrial impacts:
-Development of new Flow Control Actuators concepts by SLM based on lightweight and downsizing designs suitable for UHBR engine configuration in contrast to conventional actuators
-Definition of design guidelines for Ti6Al4V alloy processed by SLM
-Increased knowledge about SLM manufacturing criteria for titanium large parts
-Deeper knowledge in distortion prediction numerical models
-Deeper knowledge on how the physical characteristics of the actuators manufactured with SLM process determine the results obtained in the aerodynamic and harsh environment test, under different stresses applied
-Specifically in aerodynamics tests, it will be possible to evaluate the repeatability and steadiness of the SLM process.