Overcoming Boundary-Layer Separation with Distributed Propulsion

Abstract

Strategically located propulsors are able to create constructive interference on aircraft; increasing lift, lift-drag ratios (L/D), and resilience to boundary layer separation.  Computational fluid dynamic (CFD) studies teach toward an optimal configuration with a near-zero upper-surface pitch in front of a trailing section propulsor followed by a trailing taper with 20° to 45° surface pitch from the propulsor to a trailing edge near the bottom of the lifting body (“Lift Span Tech”).  Applications benefiting from Lift Span Tech range from box trucks to high-speed intercontinental transit.  With initial propulsor power mitigating boundary layer separation, Lift Span Tech provides a high gain:loss, where the gain is in reduced drag and loss is reduced thrust from the propulsor.  Performance may be augmented with ground effect further improving L/D efficiency.  This study evaluates the sensitivity of performance to different CFD turbulence models and trailing taper pitches.  While today’s commercial approaches can reduce truck drag by about 34% with no impact on wheel friction, new Lift Span Tech is able to reduce drag by up to 84% and wheel friction by up to 90%.  The technology enables designs to allow direct solar power to fully replace liquid fuels in a wide range of vehicles.