Boundary Layer Ingestion Propulsion Benefit for Transport Aircraft

Abstract

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

Exploring Vehicle Level Benefits of Revolutionary Technology Progress via Aircraft Design and Optimization

“…The main motivation of boundary layer ingestion is to make use of the boundary layer flow for improving the engine propulsive efficiency [31], i.e., "propulsor ingests and reaccelerates airframe boundary layer" [32]. Figure 4 shows a comparative study of the boundary layer ingestion (BLI) effect on propulsive efficiency.…”

Efficient Aircraft Multidisciplinary Design Optimization and Sensitivity Analysis via Signomial Programming

“…B1. As noted by Hall et al [20], BLI on the D8.2 results in a reduction in required propulsor mechanical power of 9%. Three percent of the power savings comes from reduced jet dissipation, whereas the remainder comes from a roughly 3% increase in propulsive efficiency and decreased airframe dissipation.…”

“…The reduction in jet dissipation is modeled with a drag reduction factor, δ. Following Hall's [20] analysis, it is assumed that the propulsor ingests 40% of the fuselage boundary layer (f BLI 0.4). It is further assumed that one third of total dissipation (Φ) is surface dissipation (Φ surf ).…”

Performance bookkeeping for aircraft configurations with fuselage wake-filling propulsion integration

“…Instead of the traditional force-based calculation of drag and thrust, the benefit of BLI is measured by an integrated propulsion power [17]. Drela's method is widely applied in BLI concept studies featuring a trailing edge propulsor in the MIT and NASA D8 projects, at the Delft University of Technology and sparsely in similar projects [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41].…”