Review of hybrid laminar flow control systems

Preliminary Design and System Considerations for an Active Hybrid Laminar Flow Control System

“…Besides the environmental benefits, the forecast of increasing fuel prices leads to the demand for more fuel efficient aircraft to reduce the direct operating costs. Drag reduction can be achieved by keeping the flow in the boundary layer over the aircraft surfaces (wing, horizontal tail plane (HTP), vertical tail plane (VTP), engine nacelles, and fuselage) laminar, rather than the usual turbulent boundary layer flow [1]. A laminar boundary layer flow has approximately ten times lower friction drag than a turbulent boundary layer flow, and approximately 50% of the total aircraft drag during cruise comes from friction drag [2].…”

“…The limiting factor is the sweep angle of the wing, which is usually increased for higher cruise Mach numbers. A higher swept wing is vulnerable to crossflow instabilities, which cannot be countered by merely influencing the pressure distribution [1,3]. For conventionally swept wings of high-speed aircraft, the transition point can be delayed by removing air through boundary layer suction to damp aerodynamic instability mechanisms such as Tollmien-Schlichting instability and crossflow instability [1].…”

“…A higher swept wing is vulnerable to crossflow instabilities, which cannot be countered by merely influencing the pressure distribution [1,3]. For conventionally swept wings of high-speed aircraft, the transition point can be delayed by removing air through boundary layer suction to damp aerodynamic instability mechanisms such as Tollmien-Schlichting instability and crossflow instability [1]. The LFC technique, in which the 2 of 30 air is sucked over the entire wing, has the disadvantages of causing structural issues when interfering with the wing box and the available space for fuel is reduced due to the complex and heavy suction system [2].…”

“…The HLFC system can either be passive (requiring no continuous energy input) or active (requiring energy input). It reduces aircraft skin friction drag by boundary layer suction along the leading edge, and has been investigated in research institutions and industry since the 1970s [1,5]. The first commercial aircraft, modified with an HLFC system for flight test purposes, was equipped with a heavy suction system to be as flexible as possible [6].…”

Theoretical Modeling and Optimization of Porous Coating for Hypersonic Laminar Flow Control

“…I. Introduction V ARIOUS techniques have been developed to prevent or delay hypersonic boundary-layer transition [1][2][3]. One of the most promising control technologies is the passive porous coating concept proposed by Fedorov et al [4] because of its minimal effect on mean flow and the effective suppression of the most unstable boundarylayer instability: namely, the Mack second mode [5][6][7].…”