Derivation of a Wind Tunnel Configuration for a Mid-Range Aircraft with Rear-Mounted BLI Engines

Comprehensive evaluations of the Boundary Layer Ingestion technology require in-depth analysis of both, numerical flow simulations and meaningful experiments in wind tunnels. the latter are needed for validating various models employed in flow simulations. Therefore, wind tunnel experiments must be designed to represent the flow physics of the intended technology. This study focuses on the differences occurring in a wind tunnel compared to a full-scale configuration and how to derive a model that is representative of the design point. For this purpose, numerical simulations have been carried out for both conditions to be compared. While geometrical scaling has been employed, to scale the boundary conditions of the engine, two different approaches, Mach similarity and keeping the u-velocity ratio at freestream and fan face identical, have been investigated. The results show, that using a Mach similarity at the fan face to scale the boundary conditions generated larger shock strengths for the model configuration in conjugation with a lower inlet distortion coefficient compared to the full-scale case. The velocity scaling approach matched better in this regard, as well as when comparing the overall flow field near the fan. However, it sacrifices the need to keep the tip Mach number of the propulsive fan identical between the model and the full-scale configuration. Both model set-ups could not capture potential shock development at the start of the inlet ramp, making it important to carefully monitor inlet ramp flows when designing a suitable geometry, as this significantly impacts the fan distortion and local flow field.