Periodic Reporting for period 3 - RHEA (Robust- and sustainable-by-design ultra-higH aspEct ratio wing and Airframe) Reporting period: 2023-04-01 to 2023-11-30 Summary of the context and overall objectives of the project The next generation of civil transport aircraft is required to have a significantly lower emission than the current aircraft to address the severe problem of climate change. To achieve this goal, various technologies and aircraft configurations are suggested to be integrated. Electric/hybrid-electric propulsion systems, active flow control, active load alleviation, and novel configurations such as blended wing body are currently being investigated. Ultra-High Aspect Ration Wings (UHARW) are promising solutions for reducing aircraft-induced drag, and hence reducing emissions. However, designing aircraft with UHARW faces serious challenges since increasing the aspect ratio negatively influences the wing structural weight and aeroelasticity.The RHEA project is investigating intelligent solutions for escalating the TRL of UHARW for civil transport aircraft. The solution of RHEA is to integrate novel airframe technologies, i.e. active laminar flow control, active load alleviation, advanced structures and materials with novel aircraft configurations, i.e. strut-braced wing and twin fuselage. However, the design of aircraft with novel configurations and novel technologies required novel design methodologies and tools. Therefore, RHEA is aiming to develop beyond state-of-the-art methods and tools to design novel aircraft with disruptive configurations and novel airframe technologies and investigate the influence on reducing emissions and noise.A numerical framework for MDO as well as modelling methodologies for coupled aero-structural mid-fidelity aircraft design were developed and implemented, including a higher-order correction method to account for nonlinear aircraft aerodynamics. The resulting 2-level MDO process was implemented and tested for the design of strut-braced wing (SBW) aircraft. Based on this processes, different aircraft configurations were designed on a conceptual basis. Specifically, short-range, mid-range and long-range configurations were developed, each for a strut-braced wing configuration and for a twin-fuselage configuration. As based on these results a strut-braced wing concept does have potential for short-range configurations, whereas for mid or long ranges the twin-fuselage configurations showed slightly more potential.In a final step, high fidelity evaluation tools, namely CFD and acoustics simulations based on scale-resolved flow fields, were used to analyse sensitivities and critical aspects. The analysis showed that the main sensitivities of a strut-brace wing are very similar to the ones of more conventional cantilever wing. For the aeroacoustics it was found out, that the major contributor from a strut-braced wing is the trailing edge noise from the strut, which is much larger than the noise generated near the attachment point of the strut on the wing. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far The work of the RHEA project is based on a thorough literature review and analysis of TRL of existing and promising technologies for UHARW configurations. It comprised the following elements• Developing an entire aircraft conceptual design framework capable of clean-sheet design and sizing of strut-braced and twin-fuselage aircraft equipped with novel airframe technologies such as active flow control, active load alleviation, and advanced structures and materials. • Executing this framework for conceptual design of six different aircraft in three categories: A strut-braced and a twin-fuselage configuration for each category of short-range, mid-range, and long-range passenger aircraft. The conceptual aircraft design reveal that strut-bracing and twin-fuselage configurations are important enablers of UHARW, with twin-fuselage being more effective for mid-range and long-range applications, although at lower TRL level.• Uncertainty characterization and sensitivity analysis of all the six reference aircraft of RHEA to investigate the robustness of these aircraft and identify the best designs from the robustness aspect. • Developing coupled-adjoint aerostructural analysis and optimization toolbox for analysis and optimization of strut-braced wing configurations. • Developing a fast method for dynamic aeroelastic analysis and optimization of very high aspect ratio (geometrically nonlinear) aircraft configurations, including strut-braced wings. Integration of aerostructural, aeroelastic, and aerodynamics methods within a multidisciplinary and multi-level design and optimisation (MDO) framework. The development of the MDO framework was completed in RP2, but with significant delays relative to the original project plans. Therefore, application of the framework for short range and mid-range configurations was not possible.• Simulation of UHARW configurations with high-fidelity methods for in-depths analysis aerodynamic, aero-elastic, and aero-acoustic characteristics and performance. • Because of the significant delays in the availability of the MDO framework, the work plan for high-fidelity analysis was amended. The amended RHEA project has investigated the strut-braced wing configuration developed by the U-HARWARD project. The necessary simulations were started in RP2 and high-fidelity simulations to support aerodynamic, aeroacoustic and flutter analysis were completed in RP3.• An comparative assessment of different enabling technologies for ultra-high aspect ratio wing was finally developed, supported by a critical review of the state of the art. This has resulted in a technology roadmap that blends the available open literature on UHARW technologies with the insights obtained during the RHEA project. 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 conceptual aircraft design work and the related analyses of sensitivities and uncertainties revealed new knowledge on high-performance aircraft beyond state of the art. Only by combining the enabling configurations needed for high-aspect ratio wings with advanced technologies as laminar flow control, load reduction, and new light-weight structures will allow to achieve drastic reductions of fuel burn and aircraft emissions. The newly developed bilevel MDO framework allows multi-level design beyond state of the art, but it is computationally expensive. The experienced complexity of setting up and maintaining suitable multi-level design environment therefore bears risks for the timely development of future aircraft with ultra-high aspect-ratio wings that should be carefully monitored. The high-fidelity flutter simulations on the strut-braced wing configuration highlighted the risk in the design of high-performing air vehicles without considering aeroelastic constraints. A detailed investigation showed that relatively small modifications to the strut design are likely to result in acceptable designs, without a major penalty in performance. Preliminary results on conceptual design - Rendering of the mid-range mission aircraft
