Periodic Reporting for period 2 - AFC4TR (Active Flow Control for Tilt Rotor) Reporting period: 2022-01-01 to 2022-12-31 Summary of the context and overall objectives of the project The Covid pandemic had a large influence on travel by air in the years 2020 to 2022, but already shortly after the travel restrictions have been lifted air travel is approaching the levels before the pandemic, and it expected that passenger and freight traffic will continue to increase over the next two decades. One of the main challenges that the aviation industry is facing today is to reduce its negative impacts on the environment. The Next Generation Civil Tilt Rotor (NGCTR) is a novel concept that combines the benefits of a helicopter with the speed and the capabilities of a fixed wing aircraft. A Technology Demonstrator will be built to validate its architecture, technologies /systems and operational concepts. One of the studies to be made concern the use of Active Flow Control using so called ZNMF (Zero Net Mass Flux) devices to increase the aerodynamic efficiencies of lifting surfaces. This might decrease the fuel burn, and the associated NOx and CO2 emissions. Although Active Flow Control has been studied for more than 50 years, its application is still not seen on aircraft for various reasons among them integration and power supply, reliability and certification requirements. Designing a novel aircraft configuration that from the start envisages the use of ZNMF devices might lead to a breakthrough in the use of these devices for future, and possibly existing aircraft.The use of ZNMF devices on a tilt rotor configuration has rarely been studied, and the AFC4TR project will fill this gap in knowledge.The overall objective of the AFC4TR project is to investigate the use of Active Flow Control using so called pulsed air blowing devices with Zero Net Mass Flux (ZNMF) devices on the NGCTR. This overall objective is translated into the following technical objectives:• Perform CFD simulations on the NGCTR to identify possible regions of separated and vortical flow that could benefit from ZNMF devices. • Perform unsteady CFD simulations on the NGCTR using ZNMF devices at the regions identified above. Investigate parameters that influence the operation of these devices as for example the actuation frequency, the jet velocity and the jet orientation.• Perform a multi objective optimization study in order to optimize the locations and parameters of the ZNMF devices that will bring the desired aerodynamic benefits. • Analyse the results of the study carried out and prepare recommendations for the use of ZNMF devices on the NGCTR. The AFC4TR project started in September 2020, and finished at the end of December 2022. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far In the first phase of the project unsteady CFD simulations were made for the NGCTR to identify critical regions that could benefit from the use of ZNMF devices. As a result, 3 configurations were identified that could potentially benefit from the use of ZNMF devices: 1) a clean configuration, 2) a configuration with a deflected nacelle, and 3) a configuration with a downward deflected aileron. The targets to be reached through the use of ZNMF devices are a gain of 10% in maximum lift coefficient for configurations 1 and 2, and a gain of 10% in roll moment coefficient for configuration 3.In the 2nd phase of the project a literature study was made on possible ZNMF devices, and the ASPIC synthetic jet actuator developed by Cedrat technologies was selected for the AFC4TR studies because it provides high exit velocities and high jet frequencies. This was followed by 2D CFD simulations for an airfoil with flap to study different parameters of the ZNMF device. These studies were extended to 3D studies (wing with flap). The conclusions of these studies were that to be effective, the ZNMF devices should be placed just upstream of the flow separation, that a high blowing velocity should be favored, and that the jet frequency should be around 50-100 Hz.Based on these results unsteady CFD simulations were made for the 3 configurations of the NGCTR with ZNMF devices, using a jet velocity of 300 m/s and a jet frequency of 65 Hz. In these initial CFD simulations 3 pairs of ZNMF devices were placed on the wing for configurations 1 and 2, or on the aileron for configuration 3. Results of these initial CFD simulations showed that the ZNMF devices had an influence on the flow, but that their locations need to be optimized.For NGCTR configuration 1 a total of 11 unsteady CFD simulations were made using different numbers of ZNMF devices (ranging from 6 to 20), placed at different locations. From the results obtained it was concluded that using ZNMF devices on this configuration will not lead to aerodynamic benefits. For NGCTR configuration 2 the main focus was on the case with 12o angle of attack. For this configuration 9 unsteady CFD simulations were made using 6 to 20 ZNMF devices at different locations on the wing. For this configuration the ZNMF devices permitted to reduce the massive flow separation on the wing, and a gain in lift of 5.67% was obtained compared to the case without ZNMF devices. However, for this configuration there remain open questions concerning the optimal location of the ZNMF devices, and the influence of the grid on the results. One additional unsteady calculation with ZNMF devices was made for the configuration with 8o angle of attack. At this angle of attack the flow separation in the middle of the wing is reduced in size, and as a result the ZNMF devices have only a small influence.For NGCTR configuration 3 seven unsteady CFD simulations were made using 3 pairs of ZNMF devices at different locations in the chordwise direction on the aileron. When placing the ZNMF devices just upstream of the flow separation it was possible to increase the roll-moment of the aircraft by 3.3%. The results of the AFC4TR project were widely disseminated: • 2 news letters were published • Several announcements on LinkedIn and researchgate.com • 11 papers or presentations were given at conferences and workshops during the project, and these papers or presentations were made publicly available • 1 paper was given at a conference after the project (January 2023) • 1 paper has been accepted with minor modifications for a peer reviewed journal • 2 papers will be submitted to peer reviewed journals in 2023Finally, the results of the AFC4TR project will be exploited by the project partners in future national or EU funded projects. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) The ambition of the AFC4TR project was to demonstrate that active flow control using ZNMF devices will bring aerodynamic benefits for the next generation civil tilt rotor aircraft. The project showed that the adopted modeling of ZNMF devices was successful, and could be applied for complex aircraft configurations. The project also showed that it was possible to make, on a routine base, high fidelity numerical simulations using ZNMF devices on a full aircraft configuration. In the course of the project around 40 unsteady CFD simulations using ZNMF devices were made on the NGCTR aircraft, with each calculation taking between 6 to 8 weeks of elapse time in order to get the required number of rotor rotations for the flow to establish. To our knowledge making routinely unsteady high fidelity CFD simulations modeling ZNMF devices on a full aircraft has never been done before, and the AFC4TR project clearly went beyond the state of the art at the start of the project. NGCTR configuration with ZNMF devices on the wing NGCTR configuration with active ZNMF devices Results of simulations over a 3D wing + flag with and without ZNMF devices Grid NGCTR showing the chimera grids over the rotors, engine and aileron. Skin friction lines of the NGCTR simulation with tilted nacelle.
