In a bid to meet the requirements on drag reduction, consumer demands and the latest regulations on carbon emissions and noise, aircraft manufacturers are continually looking at new technologies to improve performance. The aerospace industry is also looking to achieve the mutual benefit of combining existing technologies with new concepts to enhance transonic aerodynamic performance. With the power of modern computing, scientists and engineers can conduct Computational Fluid Dynamics (CFD) simulations for various aircraft configurations to test potential improvements by saving both prototyping and experimental costs.
This research project considers the Hybrid Electric Distributed Propulsion (HEDP) concept with under (UWN) and over-wing nacelle (OWN) configurations for large transonic transport aircraft. It examines the potential benefits of integrated UWN and OWN configurations including: (1) the effect of the fan in controlling rear adverse pressure gradients to maintain a safe operating margin between cruise and buffet, (2) providing Mach flexibility, and (3) potential performance benefits of an integrated fan design compared with traditional under-wing podded engines that can generate strong shock waves in gully regions at off-design conditions. The research also considers a design approach to improve the drag standard of a typical supercritical aerofoil by optimising its shape to minimise/eliminate the strength of shock waves. This was achieved by combining the well-known CST aerofoil parametrisation method and a four-dimensional Optimal Latin Hypercube Design of Experiments.
This research project relies on numerical analysis to investigate the flow mechanism associated with the aerodynamic performance of HEDP for both nacelle configurations. Through this research project, the distributed UWN configuration provides 87.46% in sectional drag reduction compared to the conventional podded engine configuration. Similarly, drag is reduced by 40.96% for the OWN configuration. However, it should be noted that the two-dimensional (2D) analysis of the conventional podded engine configuration is not truly representative of a three-dimensional (3D) flow field. Both of these results are achieved with an increase in aerofoil thickness which would be expected to also contribute to a wing weight reduction.
Further 3D computational research, and experimental verification is recommended for future research activities. The scope of this study was largely two-dimensional but it will be important for next steps in this research direction to account for more complex 3D effects, such as cross-flow and swirl; these considerations will be important to fully exploit potential improvements in aerodynamic performance for transonic wing designs.
