This paper highlights recent activities associated with the design of an uninstalled open fan propulsor for next-generation civil aircraft in the high-subsonic flight regime. The concept comprises a transonic propeller–rotor and a subsequent guide vane, which are both subject to pitch-variability in order to account for the strong variations in flight conditions over the entire mission profile. The engine-scale design aimed for high technological maturity and to comply with a high number of industrially relevant requirements to ensure a competitive design, meeting performance requirements in terms of high efficiency levels at cruise and maximum climb conditions, operability in terms of stability margins, good acoustic characteristics, and structural integrity. During the design iterations, rapid 3D-RANS-based optimisations were only used as a conceptual design tool to derive sensitivities, which were used to support and justify major design choices in addition to established relations from propeller theory and common design practice. These design-driven optimisation efforts were complemented with more sophisticated CFD analysis focusing on rotor tip vortex trajectories and resulting in unsteady blade row interaction to optimise the guide vane clipping, as well as investigations of the entire propulsor under angle-of-attack conditions. The resulting open fan design will be the very basis for wind tunnel experiments of a downscaled version at low and high speed.

Adjoint-based optimization methods, that were previously in the realm of computational fluid dynamics (CFD) research, are now available in commercial software. This work explores the use of adjoint-based optimization to maximize mixing and combustion efficiencies for a supersonic combustor. To this end, a two-dimensional combustor was considered with parallel hydrogen injection. Simulations were carried out based on the steady Reynolds-Averaged Navier–Stokes equations and optimization was performed using a simplified passive scalar field instead of the full reactive flow problem. The optimization of a triangle-shaped mixing element is considered in addition to a case allowing the entire bottom of the combustor to deform. The relatively small mixing element could not boost efficiency significantly. By comparison, the optimization of the combustor wall resulted in both mixing and combustion efficiency gains accompanied by total pressure loss penalty. The optimization achieved higher efficiency compared to the baseline by extending the total volume of the reaction zone. The presented proof-of-concept results are relevant for the design of hypersonic vehicle propulsion systems, such as scramjets.