Analysis of the Aerodynamic Benefit from Boundary Layer Ingestion for Transport Aircraft

Abstract

Propulsors with boundary layer ingestion (BLI) generate a propulsive force with lower flow power input than conventional engines. This aerodynamic benefit can be traced back to its sources: reductions in jet, surface, and wake dissipation. A framework for BLI analysis is developed based on the power balance method: parametric expressions are derived for the net streamwise force on an aircraft and for the mechanical flow power required, as well as relations for the dissipation components. They illustrate the range of possible comparisons between BLI and non-BLI engine installations, and show how the benefit varies with design choices. Applying the framework to wind tunnel data from powered D8 aircraft model tests, the sources of aerodynamic BLI benefit are quantified for a realistic transport aircraft configuration. With the same propulsors (equal nozzle area) BLI reduces cruise power by 8.2%, of which 5.2% comes from a reduction in jet dissipation, 2.4% from reduced surface dissipation, and 0.6% from reduced wake dissipation. The jet dissipation reduction is equivalent to a 3.4 percentage points increase in propulsive efficiency. If the installations are compared at equal mass flow, the benefit amounts to a 9% lower cruise power.