Boundary-Layer Suction System Design for Application to a Laminar Flying Wing Aircraft

Abstract

Growing air travel, with its associated environmental impact, is increasingly becoming a public concern. The laminar-flying-wing aircraft, which utilises boundary-layer suction as a means of laminar-flow control, has been proposed by Greener by Design as a potential solution, with preliminary estimates suggesting a significant reduction in fuel-burn per passenger of up to 70%. The present study aims to provide insight into the parameters affecting practical laminar-flow-control suction power requirements for a commercial laminar-flying-wing transport aircraft. It is shown that there is a minimum power requirement independent of the suction system design, associated with the stagnation pressure loss of an ‘optimal’ suction distribution which maintains a neutrally stable laminar boundarylayer. Variation from the optimal suction distribution due to a practical, chamber-based, architecture is found to have very little effect on the overall suction coefficient; hence, to a good approximation, the power penalty is given by the product of the optimal suction flow-rate coefficient and the average skin pressure drop. In the spanwise direction, through suitable choice of chamber depth, the effect of the chamber pressure drop due to frictional and inertial effects may be taken as negligible. Finally, if there are fewer pumps than chambers, it is the average pressure drop from the aerofoil surface to the pump collector ducts, rather than to the chambers, that determines the power penalty. For the representative laminar-flying-wing aircraft parameters considered here, the minimum power associated with boundary-layer losses alone contributes around 80% to the total power requirement.