SUMMARYThe present work predicts the formation of laminar separation bubbles at low Reynolds numbers and the related transition to turbulence by means of Implicit Large Eddy Simulations with a high-order Discontinuous Galerkin method. The flow around an SD7003 infinite wing at an angle of attack of 4 • is considered at Reynolds numbers of 10 000, 22 000, and 60 000 in order to gain insight into the characteristics of the laminar and turbulent regimes. At the lowest Reynolds number studied, the flow remains laminar and two dimensional over the wing surface, with a periodic vortex shedding. For higher Reynolds numbers, the flow is unsteady over the upper wing surface and exhibits a separation bubble along which the flow transitions to turbulence. Tollmien-Schlichting (TS) waves are observed in the boundary layer, and transition is found to be caused by unstable TS modes as revealed by the growth of the stream-wise amplification factor.

This paper presents a description of the physical principles of aerodynamic power savings from boundary layer ingestion (BLI) propulsion and a quantitative evaluation of the BLI benefit for advanced civil aircraft. Control volume and one-dimensional analyses are used to illustrate two major features of BLI: reduction of jet mixing losses due to decreased jet kinetic energy from reduced velocity of flow entering the propulsor and, to a lesser extent reduction of airframe wake mixing losses. Embedded BLI propulsion systems can also enable nacelles with reduced surface area and associated weight and drag, further decreasing the aircraft propulsive power requirement. The required propulsor flow power is shown to decrease with increases in both the amount of boundary layer ingested and the propulsor mass flow, and there is thus no unique way to compare BLI and non-BLI systems. Using the ideas presented, however, the benefit can be assessed for any given comparison. The analysis is applied to an advanced civil transport aircraft concept with 40% of the fuselage boundary layer ingested, yielding a reduction in required propulsor mechanical power of 9% relative to a non-BLI configuration with the same propulsors, in agreement with CFD calculations and wind tunnel