Parametric Design of a Buried Engine Intake for a Highly Swept Transonic Wing

Abstract

Closer propulsion-airframe integration through the use of boundary layer ingesting promises significant improvements in aircraft fuel consumption. However, little research has been performed on how these intakes are to be designed for swept-wing aircraft. In this study, a trailing-edge-mounted, parametrically designed buried engine intake is designed for a highly swept transonic wing. To connect the wing to the nacelle, two diagonal ramps are created. These allow for a smooth transition between the two, while minimizing the wetted area and allowing more control over the bottom surface of the connection. The intake is initially designed as an axisymmetric body, after which the intake is reshaped to allow for elliptical highlight and throat profiles. The intake duct can also be angled left and right, up and down, to align it with the incoming flow. This is a key feature, as a highly swept wing causes a significant level of cross-flow. Since the engine is placed near the trailing edge, there is also a large downwashing component to the flow. By angling the intake, it can be aligned with the flow. The intake is designed and parameterized in 3DX’s CATIA to allow quantifiable changes to be made to the design. The designs are tested using a compressible RANS simulation with a 𝑘 − 𝜔 SST turbulence model and third-order MUSCL spatial discretization at 𝑀 = 0.85, 𝐶𝐿 = 0.1719, and 𝑅𝑒 = 104.8 million. The initial baseline design has a TPR of 0.973, despite a section of flow reversal at the crown of the intake, equal to 3.8% of the fan area. The ingested boundary layer is significantly thickened ahead of the intake due to excessive curvature. This causes a DC60 of 0.349, unacceptable for modern aero-engines. The lift coefficient has increased by 12.2%, mainly caused by a sectional lift increase outboard of the engine. The drag coefficient has increased by 4.8%, although the wetted area has increased by 8.8%, indicating an increase in aerodynamic efficiency. The highest pressure recovery found is 0.985 for version 1 and is acceptable compared to conventional podded engines. However, it still featured a large portion of separated and reversed flow at the crown. Therefore, 5 further iterations were made, finally arriving at an intake with a similar TPR of 0.983, but with almost no reversed flow. The remaining total pressure losses are predominantly caused by the ingestion of the wing’s boundary layer. The DC60 has reduced to 0.171, while the SC60 is 0.0874. The lift coefficient has remained the same w.r.t the baseline design, but the drag coefficient has significantly reduced, being 3.0% less than that of the clean wing. During the iteration process, the angling of the intake into the flow was found to be most critical when trying to improve performance. Specifically, the centerline toe angle, angle of incidence, and throat offset were found to have the greatest effect on the flow quality at the fan face.